View Full Version : Disintegrating Planets - some recent news

Roger E. Moore
2018-Jul-30, 07:24 PM
Nothing says weird like a disintegrating exoplanet. There are supposed to be 3-4 of them, and here are some 2018 updates.



Radial Velocity Follow-up of the Disintegrating Planet KIC 12557548b

Kento Masuda, Teruyuki Hirano, Hajime Kawahara, and Bun'ei Sato
2018 March 30

KIC 12557548b is an ultra-short-period (0.65 days) planet observed with the Kepler spacecraft, whose transit light curves exhibit depth variations and asymmetric morphology (Rappaport et al. 2012). These features are ascribed to disintegration of the rocky planet, but it may also be worth considering less extraordinary explanations. For example, a giant planet or stellar companion on an eccentric and grazing orbit, perturbed by a third body, could produce transit depth variations via varying orbital inclinations, and asymmetric "transits" via tidal distortion of the star as observed in heartbeat binaries. Such an alternative can be tested by measuring radial velocities (RVs) over the whole orbital phase.

We obtained high-resolution (R ~ 60,000) spectra of KIC 12557548 with the High Dispersion Spectrograph (HDS, Noguchi et al. 2002) installed on the Subaru 8.2 m telescope (proposal S15B-163). The observations were performed on UT 2015 August 27 and 28 to obtain five 40 minute exposures each night, with the standard Ra setup covering 5107–7787 Å. The signal to noise per pixel was 20–30 around 5800 Å.

We performed standard reduction and wavelength calibration using Th–Ar spectra obtained before and after each exposure. Only the data from red CCDs were analyzed to apply telluric corrections (see below). We normalized the spectra and removed OH night-sky emissions using the list in Osterbrock et al. (1996), as well as cosmic-ray outliers. The spectra were then interpolated and cross-correlated with the theoretical spectrum (Coelho et al. 2005) for atmospheric parameters similar to KIC 12557548 to derive RV shifts. The RV value and its error for each exposure were obtained as the mean and its standard error calculated from the shifts in nine orders without heavy telluric contaminations or bad-quality data, and the barycentric correction was applied.

These RVs were further calibrated using telluric lines following Chubak et al. (2012). We used the SKYCALC Sky Model Calculator 7 to produce a model telluric spectrum with R = 300,000, and used it to measure velocity shifts in two wavelength ranges (7594–7621 Å and 6867–6884 Å) containing oxygen A and B bands. The average of the two was used to calibrate RV zero points.

The resulting RVs (Figure 1) were constant within ~100 m s−1 and consistent with Keck/HIRES values from Croll et al. (2014), thus providing further evidence for the disintegrating planet scenario. We used emcee (Foreman-Mackey et al. 2013) to fit the combined RV time series assuming the circular Keplerian orbit. The ephemerides were fixed at the values in the KOI catalog and uniform priors were imposed on the RV semi-amplitude K and systemic RV. We found K < 86 m s−1 as the 95th percentile of the marginal posterior. Adopting the host star mass of 0.67 M ⊙, this translates into the upper limit on the planetary mass m < 89 M ⊕.



Chromatic transit light curves of disintegrating rocky planets

A. R. Ridden-Harper, C. U. Keller, M. Min, R. van Lieshout, I. A. G. Snellen
(Submitted on 20 Jul 2018)

Context. Kepler observations have revealed a class of short period exoplanets, of which Kepler-1520 b is the prototype, which have comet-like dust tails thought to be the result of small, rocky planets losing mass. The shape and chromaticity of the transits constrain the properties of the dust particles originating from the planet's surface, offering a unique opportunity to probe the composition and geophysics of rocky exoplanets.
Aims. We aim to approximate the average Kepler long-cadence light curve of Kepler-1520 b and investigate how the optical thickness and transit cross-section of a general dust tail can affect the observed wavelength dependence and depth of transit light curves.
Methods. We developed a new 3D model that ejects sublimating particles from the planet surface to build up a dust tail, assuming it to be optically thin, and used 3D radiative transfer computations that fully treat scattering using the distribution of hollow spheres (DHS) method, to generate transit light curves between 0.45 and 2.5 μ m.
Results. We show that the transit depth is wavelength independent for optically thick tails, potentially explaining why only some observations indicate a wavelength dependence. From the 3D nature of our simulated tails, we show that their transit cross-sections are related to the component of particle ejection velocity perpendicular to the planet's orbital plane and use this to derive a minimum ejection velocity of 1.2 kms −1. To fit the average transit depth of Kepler-1520 b of 0.87%, we require a high dust mas-loss rate of 7−80 M⊕ Gyr −1 which implies planet lifetimes that may be inconsistent with the observed sample. Therefore, these mass-loss rates should be considered to be upper limits.



The Ongoing Evolution of the K2-22 System

Colon, Knicole D.; Zhou, George; Shporer, Avi; Collins, Karen A.; Bieryla, Allyson; Latham, David W.; Espinoza, Nestor; Murgas, Felipe; Pattarakijwanich, Petchara; Awiphan, Supachai; TECH Collaboration

Of the thousands of exoplanets known, only three disintegrating planets have been identified. These disintegrating planets appear to have tails of dusty material that produce asymmetric transit shapes. K2-22b is one of these few disintegrating planets discovered to date, and its light curve not only displays highly variable transit depths but also uniquely displays evidence of a leading dust tail. Here, we present results from a large ground-based photometric observing campaign of the K2-22 system that took place between December 2016 and May 2017, which we use to investigate the evolution of the transit of K2-22b. Last observed in early 2015, in these new observations we recover the transit around the expected time and measure a typical depth of <1%. We find that the transit depth has decreased compared to observations from 2014 and 2015, where the maximum transit depth measured at that time was ~1.3%. These new observations support ongoing variability in the transit depth, shape, and time of K2-22b, although the overall shallowness of the transit makes a detailed analysis of the transit shape and timing difficult. In addition, we find no strong evidence of wavelength-dependent transit depths for epochs where we have simultaneous coverage at multiple wavelengths. Given the observed decrease in the transit depth between 2015 and 2017, we encourage continued high-precision photometric monitoring of this system in order to further constrain the evolution timescale and to aid comparative studies with the other few disintegrating planets known.



Transiting Disintegrating Planetary Debris around WD 1145+017

Andrew Vanderburg and Saul A. Rappaport

More than a decade after astronomers realized that disrupted planetary material likely pollutes the surfaces of many white dwarf stars, the discovery of transiting debris orbiting the white dwarf WD 1145+017 has opened the door to new explorations of this process. We describe the observational evidence for transiting planetary material and the current theoretical understanding (and in some cases lack thereof) of the phenomenon.



Light-curve analysis of KOI 2700b: the second extrasolar planet with a comet-like tail

Z. Garai
(Submitted on 20 Dec 2017)

The Kepler object KOI 2700b (KIC 8639908b) was discovered recently as the second exoplanet with a comet-like tail. It exhibits a distinctly asymmetric transit profile, likely indicative of the emission of dusty effluents and reminiscent of KIC 12557548b, the first exoplanet with a comet-like tail. The scientific goal of this work is to verify the disintegrating-planet scenario of KOI 2700b by modeling its light curve and to put constraints on various tail and planet properties, as was done in the case of KIC 12557548b. We obtained the phase-folded and binned transit light curve of KOI 2700b, which we subsequently iteratively modeled using the radiative-transfer code SHELLSPEC. We modeled the comet-like tail as part of a ring around the parent star and we also included the solid body of the planet in the model. During the modeling we applied selected species and dust particle sizes. We confirmed the disintegrating-planet scenario of KOI 2700b. Furthermore, via modeling, we derived some interesting features of KOI 2700b and its comet-like tail.

John Mendenhall
2018-Jul-30, 09:52 PM
Amazing. Thank you !

Roger E. Moore
2018-Jul-31, 01:10 AM
A few more recent (2017-2018) papers to round things out.


Multi-Wavelength Photometric Study of the Transits of an Extrasolar Asteroid

Xu, Siyi

White dwarf WD 1145+017 is recently discovered by K2 to be orbited by at least one actively disintegrating asteroid. There are deep, broad, and evolving transits in the star's light curve. Here, we present multi-wavelength photometric observations from ultraviolet (Hubble), optical (multiple telescopes), K band (VLT) and 4.5 micron (Spitzer). Nominally, the transit depths are different in all the observed wavelengths. After correcting for contaminations from circumstellar lines in the ultraviolet and dust emission in the infrared, we find no difference in the transit depth. This can be explained by a deficit of small dust particles in the transiting material. We propose a model wherein only large partices can survive the high equilibrium temperature environment around WD 1145+017, while small particles sublimate rapidly. WD 1145+017 is a unique system that allows us to perform a detailed characterization of an extrasolar asteroid.



Constraining properties of disintegrating exoplanets

Dimitri Veras, Philip J. Carter, Zoë M. Leinhardt and Boris T. Gänsicke

Evaporating and disintegrating planets provide unique insights into chemical makeup and physical constraints. The striking variability, depth (∼10 − 60%) and shape of the photometric transit curves due to the disintegrating minor planet orbiting white dwarf WD 1145+017 has galvanised the post-mainsequence exoplanetary science community. We have performed the first tidal disruption simulations of this planetary object, and have succeeded in constraining its mass, density, eccentricity and physical nature. We illustrate how our simulations can bound these properties, and be used in the future for other exoplanetary systems.
...We find that primarily rocky differentiated bodies with moderate (∼3–4 g cm-3) bulk densities on nearcircular (e ~︎ 0.1) orbits can remain intact while oc- casionally shedding mass from their mantles. These results suggest that the asteroid orbiting WD 1145+017 is differentiated, resides just outside of the Roche radius for bulk density but just inside the Roche radius for mantle density, and is more akin physically to an asteroid like Vesta instead of one like Itokawa.



Disintegrating Rocky Exoplanets

Rik van Lieshout, Saul Rappaport
(Submitted on 2 Aug 2017)

Three exoplanets have been discovered with the Kepler mission that are inferred to have tails of dusty effluents trailing behind (or even ahead) of them in orbit about their host star (Rappaport et al. 2012, 2014; Sanchis-Ojeda et al. 2015). These objects, known respectively as KIC 12557548b (KIC 1255b for short), KOI-2700b, and K2-22b, have several characteristics in common. The orbital periods are all quite short at 15.7, 22, and 9.5 hours, respectively. The depths of the occultations as they pass in front of their host stars range from 0.02% to 0.5%, which imply blocking areas of 1−18 times that of the Earth. However, the occultations are asymmetric about their midpoint, and are otherwise inconsistent with transits of solid-body planets. Importantly, the transit depths of all three objects vary with time – KIC 1255b and K2-22b exhibit rapid variations in depth from transit to transit, while those of KOI-2700b vary slowly with time over the four years of the main Kepler mission. All of these observational characteristics point toward the occulter being an elongated tail of dusty material emanating from an underlying hot rocky exoplanet. However, it should be noted up front that at present it is difficult to ascertain either the mass or the radius of these ‘disintegrating’ planets, as they have come to be known. The inferred mass-loss rates from the planets, based on the amount of dust required to yield such significant extinction of the host star, is in the range of 1010 ±1 g s−1. This translates to ∼4 lunar masses per Gyr. In turn, this implies that for rocky bodies of radius 25, 250,and 2500 km, the disintegration lifetimes would be 103 years, 1Myr, and 1 Gyr, respectively. The extremely short implied lifetimes for bodies under 1000 km, compared to the lifetimes of their host stars, suggest a rather small likelihood for discovering such objects. Therefore, in this work we assume that the disintegrating exoplanets are at least the size of Ceres, a minor planet in our solar system with a mass of 1% that of the Moon, and a radius of∼500 km. The recently discovered transits of white dwarf WD 1145+017 ... show some of the same properties as the disintegrating exoplanets...


And, of course...


Mysterious eclipses in the light curve of KIC8462852: a possible explanation

Neslušan, L.; Budaj, J.

Context. Apart from thousands of "regular" exoplanet candidates, Kepler satellite has discovered a small number of stars exhibiting peculiar eclipse-like events. They are most probably caused by disintegrating bodies transiting in front of the star. However, the nature of the bodies and obscuration events, such as those observed in KIC 8462852, remain mysterious. A swarm of comets or artificial alien mega-structures have been proposed as an explanation for the latter object.
Aims: We explore the possibility that such eclipses are caused by the dust clouds associated with massive parent bodies orbiting the host star.
Methods: We assumed a massive object and a simple model of the dust cloud surrounding the object. Then, we used the numerical integration to simulate the evolution of the cloud, its parent body, and resulting light-curves as they orbit and transit the star.
Results: We found that it is possible to reproduce the basic features in the light-curve of KIC 8462852 with only four objects enshrouded in dust clouds. The fact that they are all on similar orbits and that such models require only a handful of free parameters provides additional support for this hypothesis.
Conclusions: This model provides an alternative to the comet scenario. With such physical models at hand, at present, there is no need to invoke alien mega-structures for an explanation of these light-curves.

Roger E. Moore
2018-Aug-03, 02:32 PM

Disruption of a planet spiralling into its host star

Shi Jia, H.C. Spruit
(Submitted on 1 Aug 2018)

The processes leading deformation and destruction of planets spiraling into the convective envelope of their host stars are described. The planet is compressed by the ram pressure, and deformed into a flattened shape for which a quantitative model is developed. Compression increases the planet's density contrast with the envelope and its gravitational binding energy. This increases the survivability especially of gas planets. An estimate is given for the depth of disruption by ram pressure, and for the subsequent fragmentation of the remnants. We show how the debris of rocky or iron planets, instead of mixing through the convection zone, sinks below the base of the convection zone. The time scale of the entire sequence of events is of the order of a few orbital times of the planet. If spiral-in of (partly) icy, rocky or iron planets has happened to the pre-main sequence Sun, it could account for the higher opacity below the base of the convection zone as inferred from helioseismology.

Roger E. Moore
2018-Aug-17, 06:47 PM
A few older papers on disintegrating exoplanets that might be of interest....


A planet orbiting inside of a star.

Alexander Panin

Most of stars pass via the state of red giant during their evolution partially engulfing their planetary systems. We investigate theoretically and computationally how a planet moves inside of such star and how quickly it heats up. Surprisingly, our modeling shows that a planet does not quickly disintegrate inside of a red giant star nor does it even change its orbit quickly -- in some cases a planet continues to orbit below a photosphere of a red giant star for thousands of years, and in some other cases - for millions of years (!).


Earliest paper on "super-Mercury" KIC 12557548, calculating the evaporation rate of the planet


Possible Disintegrating Short-Period Super-Mercury Orbiting KIC 12557548

S. Rappaport, A. Levine, E. Chiang, I. El Mellah, J. Jenkins, B. Kalomeni, E. S. Kite, M. Kotson, L. Nelson, L. Rousseau-Nepton, K. Tran
(Submitted on 12 Jan 2012 (v1), last revised 24 Mar 2012 (this version, v2))

We report here on the discovery of stellar occultations, observed with Kepler, that recur periodically at 15.685 hour intervals, but which vary in depth from a maximum of 1.3% to a minimum that can be less than 0.2%. The star that is apparently being occulted is KIC 12557548, a K dwarf with T_eff = 4400 K and V = 16. Because the eclipse depths are highly variable, they cannot be due solely to transits of a single planet with a fixed size. We discuss but dismiss a scenario involving a binary giant planet whose mutual orbit plane precesses, bringing one of the planets into and out of a grazing transit. We also briefly consider an eclipsing binary, that either orbits KIC 12557548 in a hierarchical triple configuration or is nearby on the sky, but we find such a scenario inadequate to reproduce the observations. We come down in favor of an explanation that involves macroscopic particles escaping the atmosphere of a slowly disintegrating planet not much larger than Mercury. The particles could take the form of micron-sized pyroxene or aluminum oxide dust grains. The planetary surface is hot enough to sublimate and create a high-Z atmosphere; this atmosphere may be loaded with dust via cloud condensation or explosive volcanism. Atmospheric gas escapes the planet via a Parker-type thermal wind, dragging dust grains with it. We infer a mass loss rate from the observations of order 1 M_E/Gyr, with a dust-to-gas ratio possibly of order unity. For our fiducial 0.1 M_E planet, the evaporation timescale may be ~0.2 Gyr. Smaller mass planets are disfavored because they evaporate still more quickly, as are larger mass planets because they have surface gravities too strong to sustain outflows with the requisite mass-loss rates. The occultation profile evinces an ingress-egress asymmetry that could reflect a comet-like dust tail trailing the planet; we present simulations of such a tail.



Catastrophic Evaporation of Rocky Planets

Daniel Perez-Becker, Eugene Chiang (UC Berkeley)
(Submitted on 8 Feb 2013 (v1), last revised 21 May 2013 (this version, v3))

Short-period exoplanets can have dayside surface temperatures surpassing 2000 K, hot enough to vaporize rock and drive a thermal wind. Small enough planets evaporate completely. We construct a radiative-hydrodynamic model of atmospheric escape from strongly irradiated, low-mass rocky planets, accounting for dust-gas energy exchange in the wind. Rocky planets with masses < 0.1 M_Earth (less than twice the mass of Mercury) and surface temperatures > 2000 K are found to disintegrate entirely in < 10 Gyr. When our model is applied to Kepler planet candidate KIC 12557548b --- which is believed to be a rocky body evaporating at a rate of dM/dt > 0.1 M_Earth/Gyr --- our model yields a present-day planet mass of < 0.02 M_Earth or less than about twice the mass of the Moon. Mass loss rates depend so strongly on planet mass that bodies can reside on close-in orbits for Gyrs with initial masses comparable to or less than that of Mercury, before entering a final short-lived phase of catastrophic mass loss (which KIC 12557548b has entered). Because this catastrophic stage lasts only up to a few percent of the planet's life, we estimate that for every object like KIC 12557548b, there should be 10--100 close-in quiescent progenitors with sub-day periods whose hard-surface transits may be detectable by Kepler --- if the progenitors are as large as their maximal, Mercury-like sizes (alternatively, the progenitors could be smaller and more numerous). According to our calculations, KIC 12557548b may have lost ~70% of its formation mass; today we may be observing its naked iron core.



From Dust to Dust: Protoplanetary Disk Accretion, Hot Jupiter Climates, and the Evaporation of Rocky Planets

Perez-Becker, Daniel Alonso

This dissertation is composed of three independent projects in astrophysics concerning phenomena that are concurrent with the birth, life, and death of planets. In Chapters 1 & 2, we study surface layer accretion in protoplanetary disks driven stellar X-ray and far-ultraviolet (FUV) radiation. In Chapter 3, we identify the dynamical mechanisms that control atmospheric heat redistribution on hot Jupiters. Finally, in Chapter 4, we characterize the death of low-mass, short-period rocky planets by their evaporation into a dusty wind. Chapters 1 & 2: Whether protoplanetary disks accrete at observationally significant rates by the magnetorotational instability (MRI) depends on how well ionized they are. We find that disk surface layers ionized by stellar X-rays are susceptible to charge neutralization by condensates---ranging from mum-sized dust to angstrom-sized polycyclic aromatic hydrocarbons (PAHs). Ion densities in X-ray-irradiated surfaces are so low that ambipolar diffusion weakens the MRI. In contrast, ionization by stellar FUV radiation enables full-blown MRI turbulence in disk surface layers. Far-UV ionization of atomic carbon and sulfur produces a plasma so dense that it is immune to ion recombination on grains and PAHs. Even though the FUV-ionized layer is ˜10--100 times more turbulent than the X-ray-ionized layer, mass accretion rates of both layers are comparable because FUV photons penetrate to lower surface densities than do X-rays. We conclude that surface layer accretion occurs at observationally significant rates at radii ≳ 1--10 AU. At smaller radii, both X-ray- and FUV-ionized surface layers cannot sustain the accretion rates generated at larger distance and an additional means of transport is needed. In the case of transitional disks, it could be provided by planets. Chapter 3: Infrared light curves of transiting hot Jupiters present a trend in which the atmospheres of the hottest planets are less efficient at redistributing the stellar energy absorbed on their daysides than colder planets. Here we present a shallow water model of the atmospheric dynamics on synchronously rotating planets that explains why heat redistribution efficiency drops as stellar insolation rises. To interpret the model, we develop a scaling theory which shows that the timescale for gravity waves to propagate horizontally over planetary scales, tauwave, plays a dominant role in controlling the transition from small to large temperature contrasts. This implies that heat redistribution is governed by a wave-like process, similar to the one responsible for the weak temperature gradients in the Earth's tropics. When atmospheric drag can be neglected, the transition from small to large day-night temperature contrasts occurs when tauwave ˜ (taurad /o)1/2, where taurad is the radiative relaxation time of the atmosphere and o is the planetary rotation frequency. Our results subsume the more widely used timescale comparison for estimating heat redistribution efficiency between taurad and the horizontal day-night advection timescale, tauadv. Chapter 4: Short-period exoplanets can have dayside surface temperatures surpassing 2000 K, hot enough to vaporize rock and drive a thermal wind. Small enough planets evaporate completely. Here we construct a radiative-hydrodynamic model of atmospheric escape from strongly irradiated, low-mass rocky planets, accounting for dust-gas energy exchange in the wind. Rocky planets with masses ≲ 0.1 MEarth (less than twice the mass of Mercury) and surface temperatures ≳ 2000 K are found to disintegrate entirely in ≲ 10 Gyr. When our model is applied to Kepler planet candidate KIC 12557548b---which is believed to be a rocky body evaporating at a rate of dM/dt ≳ 0.1 MEarth/Gyr---our model yields a present-day planet mass of ≲ 0.02 MEarth or less than about twice the mass of the Moon. Mass loss rates depend so strongly on planet mass that bodies can reside on close-in orbits for Gyrs with initial masses comparable to or less than that of Mercury, before entering a final short-lived phase of catastrophic mass loss (which KIC 12557548b has entered). We estimate that for every object like KIC 12557548b, there should be 10--100 close-in quiescent progenitors with sub-day periods whose hard-surface transits may be detectable by Kepler---if the progenitors are as large as their maximal, Mercury-like sizes. KIC 12557548b may have lost ˜70% of its formation mass; today we may be observing its naked iron core.

Roger E. Moore
2018-Aug-17, 06:49 PM

Unstable low-mass planetary systems as drivers of white dwarf pollution

Mustill, Alexander J.; Villaver, Eva; Veras, Dimitri; Gänsicke, Boris T.; Bonsor, Amy

At least 25 {per cent} of white dwarfs show atmospheric pollution by metals, sometimes accompanied by detectable circumstellar dust/gas discs or (in the case of WD 1145+017) transiting disintegrating asteroids. Delivery of planetesimals to the white dwarf by orbiting planets is a leading candidate to explain these phenomena. Here, we study systems of planets and planetesimals undergoing planet-planet scattering triggered by the star's post-main-sequence mass loss, and test whether this can maintain high rates of delivery over the several Gyr that they are observed. We find that low-mass planets (Earth to Neptune mass) are efficient deliverers of material and can maintain the delivery for Gyr. Unstable low-mass planetary systems reproduce the observed delayed onset of significant accretion, as well as the slow decay in accretion rates at late times. Higher-mass planets are less efficient, and the delivery only lasts a relatively brief time before the planetesimal populations are cleared. The orbital inclinations of bodies as they cross the white dwarf's Roche limit are roughly isotropic, implying that significant collisional interactions of asteroids, debris streams and discs can be expected. If planet-planet scattering is indeed responsible for the pollution of white dwarfs, many such objects, and their main-sequence progenitors, can be expected to host (currently undetectable) super-Earth planets on orbits of several au and beyond.

Roger E. Moore
2018-Aug-17, 06:51 PM
Also discovered papers on two Solar System asteroids that appear to be actively breaking apart, right now.



A Most Incredible Asteroid: The Break-Up of P/2013 R3

Jewitt, David; Agarwal, Jessica; Li, Jing; Weaver, Harold A.; Mutchler, Maximilian J.; Larson, Stephen M.

We present a comprehensive study of the actively disintegrating asteroid P/2013 R3. Using the Hubble and Keck telescopes, we identified thirteen discrete components separating with a mean, pair-wise velocity dispersion of v = 0.33+/-0.03 m/s. Their separation times are staggered over an interval of 5 months. Combined, the components of P/2013 R3 would form a single spherical body with radius 400 m, which is our best estimate of the size of the precursor object. Dust enveloping the system has, in the first observations, a cross-section 30 sq. km but fades monotonically at a rate consistent with the action of radiation pressure sweeping. The individual components exhibit comet-like morphologies and also fade except where secondary fragmentation is accompanied by the release of additional dust. Upper limits to the radii of any embedded solid nuclei are typically 100 to 200 m (geometric albedo 0.05 assumed). The observations are consistent with rotational disruption of a weak (cohesive strength 50 to 100 Pa) parent body, 400 m in radius. Estimated radiation (YORP) spin-up times of this parent are less than 1 Myr, shorter than the collisional lifetime. If present, water ice sublimating at as little as 1 g/s could generate a torque on the parent body rivaling the YORP torque. Under conservative assumptions about the frequency of similar disruptions, the inferred asteroid debris production rate is 1000 kg/s, which is at least 4 percent of the rate needed to maintain the Zodiacal Cloud.The work has been recently published: D. Jewitt, J. Agarwal, J. Li, H. Weaver, M. Mutchler, S. Larson (2017). The Astronomical Journal, 153:223(17pp)



Anatomy of an Asteroid Break-Up: The Case of P/2013 R3

Dave Jewitt, Jessica Agarwal, Jing Li, Harold Weaver, Max Mutchler, Stephen Larson
(Submitted on 28 Mar 2017)

We present an analysis of new and published data on P/2013 R3, the first asteroid detected while disintegrating. Thirteen discrete components are measured in the interval between UT 2013 October 01 and 2014 February 13. We determine a mean, pair-wise velocity dispersion amongst these components of \Delta v = 0.33\pm0.03 m s^{-1} and find that their separation times are staggered over an interval of \sim5 months. Dust enveloping the system has, in the first observations, a cross-section \sim30 km^2 but fades monotonically at a rate consistent with the action of radiation pressure sweeping. The individual components exhibit comet-like morphologies and also fade except where secondary fragmentation is accompanied by the release of additional dust. We find only upper limits to the radii of any embedded solid nuclei, typically \sim100 to 200 m (geometric albedo 0.05 assumed). Combined, the components of P/2013 R3 would form a single spherical body with radius \lesssim400 m, which is our best estimate of the size of the precursor object. The observations are consistent with rotational disruption of a weak (cohesive strength \sim50 to 100 N m^{-2}) parent body, \sim400 m in radius. Estimated radiation (YORP) spin-up times of this parent are \lesssim1 Myr, shorter than the collisional lifetime. If present, water ice sublimating at as little as 10^{-3} kg s^{-1} could generate a torque on the parent body rivaling the YORP torque. Under conservative assumptions about the frequency of similar disruptions, the inferred asteroid debris production rate is \gtrsim10^3 kg s^{-1}, which is at least 4% of the rate needed to maintain the Zodiacal Cloud.



Disintegrating Asteroid P/2013 R3

David Jewitt, Jessica Agarwal, Jing Li, Harold Weaver, Max Mutchler, Stephen Larson
(Submitted on 5 Mar 2014)

Splitting of the nuclei of comets into multiple components has been frequently observed but, to date, no main-belt asteroid has been observed to break-up. Using the Hubble Space Telescope, we find that main-belt asteroid P/2013 R3 consists of 10 or more distinct components, the largest up to 200 m in radius (assumed geometric albedo of 0.05) each of which produces a coma and comet-like dust tail. A diffuse debris cloud with total mass roughly 2x10^8 kg further envelopes the entire system. The velocity dispersion among the components is about V = 0.2 to 0.5 m/s, is comparable to the gravitational escape speeds of the largest members, while their extrapolated plane-of-sky motions suggest break-up between February and September 2013. The broadband optical colors are those of a C-type asteroid. We find no spectral evidence for gaseous emission, placing model-dependent upper limits to the water production rate near 1 kg/s. Breakup may be due to a rotationally induced structural failure of the precursor body.



Split Active Asteroid P/2016 J1 (PANSTARRS)

Man-To Hui, David Jewitt, Xinnan Du
(Submitted on 9 Feb 2017)

We present a photometric and astrometric study of the split active asteroid P/2016 J1 (PANSTARRS). The two components (hereafter J1-A and J1-B) separated either \sim1500 days (2012 May to June) or 2300 days (2010 April) prior to the current epoch, with a separation speed V_{\mathrm{sep}} = 0.70 \pm 0.02 m s^{-1} for the former scenario, or 0.83 \pm 0.06 m s^{-1} for the latter. Keck photometry reveals that the two fragments have similar, Sun-like colors which are comparable to the colors of primitive C- and G-type asteroids. With a nominal comet-like albedo, p_{R} = 0.04, the effective, dust-contaminated cross sections are estimated to be 2.4 km^{2} for J1-A, and 0.5 km^{2} for J1-B. We estimate that the nucleus radii lie in the range 140 \lesssim R_{\mathrm{N}} \lesssim 900 m for J1-A and 40 \lesssim R_{\mathrm{N}} \lesssim 400 m, for J1-B. A syndyne-synchrone simulation shows that both components have been active for 3 to 6 months, by ejecting dust grains at speeds \sim0.5 m s^{-1} with rates \sim1 kg s^{-1} for J1-A and 0.1 kg s^{-1} for J1-B. In its present orbit, the rotational spin-up and devolatilization times of 2016 J1 are very small compared to the age of the solar system, raising the question of why this object still exists. We suggest that ice that was formerly buried within this asteroid became exposed at the surface, perhaps via a small impact, and that sublimation torques then rapidly drove it to break-up. Further disintegration events are anticipated due to the rotational instability.

Roger E. Moore
2018-Aug-17, 08:20 PM
Newer stuff on disintegrating asteroids. A few of these were mistaken for Main Belt Comets for a time, I think.


Asteroid Family Associations of Active Asteroids

Henry H. Hsieh, Bojan Novakovic, Yoonyoung Kim, Ramon Brasser
(Submitted on 3 Jan 2018)

We report on the results of a systematic search for associated asteroid families for all active asteroids known to date. We find that 10 out of 12 main-belt comets (MBCs) and 5 out of 7 disrupted asteroids are linked with known or candidate families, rates that have ~0.1% and ~6% probabilities, respectively, of occurring by chance, given an overall family association rate of 37% for asteroids in the inner solar system. We find previously unidentified family associations between 238P/Read and the candidate Gorchakov family, 311P/PANSTARRS and the candidate Behrens family, 324P/La Sagra and the Alauda family, 354P/LINEAR and the Baptistina family, P/2013 R3-B (Catalina-PANSTARRS) and the Mandragora family, P/2015 X6 (PANSTARRS) and the Aeolia family, P/2016 G1 (PANSTARRS) and the Adeona family, and P/2016 J1-A/B (PANSTARRS) and the Theobalda family. All MBCs with family associations belong to families that contain asteroids with primitive taxonomic classifications and low average reported albedos (pV_avg < 0.10), while disrupted asteroids with family associations belong to families that contain asteroids that span wider ranges of taxonomic types and average reported albedos (0.06 < pV_avg < 0.25). These findings are consistent with MBC activity being closely correlated to composition (i.e., whether an object is likely to contain ice), while disrupted asteroid activity is not as sensitive to composition. Given our results, we describe a sequence of processes by which the formation of young asteroid families could lead to the production of present-day MBCs.



Rotational Failure of Rubble-pile Bodies: Influences of Shear and Cohesive Strengths

Zhang, Yun; Richardson, Derek C.; Barnouin, Olivier S.; Michel, Patrick; Schwartz, Stephen R.; Ballouz, Ronald-Louis

The shear and cohesive strengths of a rubble-pile asteroid could influence the critical spin at which the body fails and its subsequent evolution. We present results using a soft-sphere discrete element method to explore the mechanical properties and dynamical behaviors of self-gravitating rubble piles experiencing increasing rotational centrifugal forces. A comprehensive contact model incorporating translational and rotational friction and van der Waals cohesive interactions is developed to simulate rubble-pile asteroids. It is observed that the critical spin depends strongly on both the frictional and cohesive forces between particles in contact; however, the failure behaviors only show dependence on the cohesive force. As cohesion increases, the deformation of the simulated body prior to disruption is diminished, the disruption process is more abrupt, and the component size of the fissioned material is increased. When the cohesive strength is high enough, the body can disaggregate into similar-size fragments, which could be a plausible mechanism to form asteroid pairs or active asteroids. The size distribution and velocity dispersion of the fragments in high-cohesion simulations show similarities to the disintegrating asteroid P/2013 R3, indicating that this asteroid may possess comparable cohesion in its structure and experience rotational fission in a similar manner. Additionally, we propose a method for estimating a rubble pile's friction angle and bulk cohesion from spin-up numerical experiments, which provides the opportunity for making quantitative comparisons with continuum theory. The results show that the present technique has great potential for predicting the behaviors and estimating the material strengths of cohesive rubble-pile asteroids.



The Nucleus of Active Asteroid 311P/(2013 P5) PANSTARRS

David Jewitt, Harold Weaver, Max Mutchler, Jing Li, Jessica Agarwal, Stephen Larson
(Submitted on 16 Apr 2018)

The unique inner-belt asteroid 311P/PANSTARRS (formerly P/2013 P5) is notable for its sporadic, comet-like ejection of dust in nine distinct epochs spread over \sim250 days in 2013. This curious behavior has been interpreted as the product of localized, equator-ward landsliding from the surface of an asteroid rotating at the brink of instability. We obtained new Hubble Space Telescope observations to directly measure the nucleus and to search for evidence of its rapid rotation. However, instead of providing photometric evidence for rapid nucleus rotation, our data set a lower limit to the lightcurve period, P \ge 5.4 hour. The dominant feature of the lightcurve is a V-shaped minimum, \sim0.3 magnitudes deep, that is suggestive of an eclipsing binary. Under this interpretation, the time-series data are consistent with a secondary/primary mass ratio, m_s/m_p \sim 1:6, a ratio of separation/primary radius, r/r_p \sim 4 and an orbit period \sim0.8 days. These properties lie within the range of other asteroid binaries that are thought to be formed by rotational breakup. While the lightcurve period is long, centripetal dust ejection is still possible if one or both components rotates rapidly (\lesssim 2 hour) and has a small lightcurve variation because of azimuthal symmetry. Indeed, radar observations of asteroids in critical rotation reveal "muffin-shaped" morphologies which are closely azimuthally symmetric and which show minimal lightcurves. Our data are consistent with 311P being a close binary in which one or both components rotates near the centripetal limit. The mass loss in 2013 suggests that breakup occurred recently and could even be on-going. A search for fragments that might have been recently ejected beyond the Hill sphere reveals none larger than effective radius r_e \sim 10 m.

Roger E. Moore
2018-Aug-21, 05:18 PM
KELT-9b, a Jovian so close to its A-type star and so hot, it is being blasted away from the atmosphere down.



A giant planet undergoing extreme ultraviolet irradiation by its hot massive-star host

B. Scott Gaudi, Keivan G. Stassun, Karen A. Collins, Thomas G. Beatty, George Zhou, David W. Latham, Allyson Bieryla, Jason D. Eastman, Robert J. Siverd, Justin R. Crepp, Erica J. Gonzales, Daniel J. Stevens, Lars A. Buchhave, Joshua Pepper, Marshall C. Johnson, Knicole D. Colon, Eric L. N. Jensen, Joseph E. Rodriguez, Valerio Bozza, Sebastiano Calchi Novati, Giuseppe D'Ago, Mary T. Dumont, Tyler Ellis, Clement Gaillard, Hannah Jang-Condell, David H. Kasper, Akihiko Fukui, Joao Gregorio, Ayaka Ito, John F. Kielkopf, Mark Manner, Kyle Matt, Norio Narita, Thomas E. Oberst, Phillip A. Reed, Gaetano Scarpetta, Denice C. Stephens, Rex R. Yeigh, Roberto Zambelli, B.J. Fulton, Andrew W. Howard, David J. James, Matthew Penny, Daniel Bayliss, Ivan A. Curtis, D.L. DePoy, Gilbert A. Esquerdo, Andrew Gould, et al. (12 additional authors not shown)
(Submitted on 21 Jun 2017)

The amount of ultraviolet irradiation and ablation experienced by a planet depends strongly on the temperature of its host star. Of the thousands of extra-solar planets now known, only four giant planets have been found that transit hot, A-type stars (temperatures of 7300-10,000K), and none are known to transit even hotter B-type stars. WASP-33 is an A-type star with a temperature of ~7430K, which hosts the hottest known transiting planet; the planet is itself as hot as a red dwarf star of type M. The planet displays a large heat differential between its day-side and night-side, and is highly inflated, traits that have been linked to high insolation. However, even at the temperature of WASP-33b's day-side, its atmosphere likely resembles the molecule-dominated atmospheres of other planets, and at the level of ultraviolet irradiation it experiences, its atmosphere is unlikely to be significantly ablated over the lifetime of its star. Here we report observations of the bright star HD 195689, which reveal a close-in (orbital period ~1.48 days) transiting giant planet, KELT-9b. At ~10,170K, the host star is at the dividing line between stars of type A and B, and we measure the KELT-9b's day-side temperature to be ~4600K. This is as hot as stars of stellar type K4. The molecules in K stars are entirely dissociated, and thus the primary sources of opacity in the day-side atmosphere of KELT-9b are likely atomic metals. Furthermore, KELT-9b receives ~700 times more extreme ultraviolet radiation (wavelengths shorter than 91.2 nanometers) than WASP-33b, leading to a predicted range of mass-loss rates that could leave the planet largely stripped of its envelope during the main-sequence lifetime of the host star.



An extended hydrogen envelope of the extremely hot giant exoplanet KELT-9b

Fei Yan, Thomas Henning
(Submitted on 2 Jul 2018)

Giant exoplanets orbiting close to their host stars have high temperatures because of the immense stellar irradiation which they receive. The extreme energy input leads to the expansion of the atmosphere and the escape of neutral hydrogen. A particularly intriguing case among the hot giant planets is KELT-9b -- an exoplanet orbiting very close to an early A-type star with the highest temperature (~4600 K at day-side) among all the exoplanets known so far. The atmospheric composition and dynamic of such a unique planet have been unknown. Here we report the first detection of an extended hot hydrogen atmosphere around KELT-9b. The detection was achieved by measuring the atomic hydrogen absorption during transit with the Balmer H{\alpha} line, which is unusually strong mainly due to the high level of extreme-ultraviolet radiation from the star. We detected a significant wavelength shift of the H{\alpha} absorption which is mostly attributed to the planetary orbital motion. The obtained transmission spectrum has a significant line contrast (1.15% extra absorption at the H{\alpha} line centre). The observation implies that the effective radius at the H{\alpha} line centre is ~1.64 times the size of the planetary radius, indicating the planet has a largely extended hydrogen envelope close to the size of the Roche lobe (1.91 R-planet) and is probably undergoing dramatic atmosphere escape.

Roger E. Moore
2018-Aug-21, 05:43 PM

Hot-Jupiter Core Mass from Roche-lobe Overflow

Sivan Ginzburg, Re'em Sari
(Submitted on 28 Nov 2016 (v1), last revised 12 May 2017 (this version, v2))

The orbits of many observed hot Jupiters are decaying rapidly due to tidal interaction, eventually reaching the Roche limit. We analytically study the ensuing coupled mass loss and orbital evolution during the Roche-lobe overflow and find two possible scenarios. Planets with light cores Mc ≲ 6 M⊕ (assuming a nominal tidal dissipation factor Q ∼10^6 for the host star) are transformed into Neptune-mass gas planets, orbiting at a separation (relative to the stellar radius) a/R⋆ ≈3.5 . Planets with heavier cores Mc ≳ 6 M⊕ plunge rapidly until they are destroyed at the stellar surface. Remnant gas-Neptunes, which are stable to photo-evaporation, are absent from the observations, despite their unique transit radius (5−10 R⊕). This result suggests that Mc ≳ 6 M⊕, providing a useful constraint on the poorly-known core mass that may distinguish between different formation theories of gas giants. Alternatively, if one assumes a prior of Mc ≈ 6 M⊕ from the core-accretion theory, our results suggest that Q does not lie in the range 10^6 ≲ Q ≲ 10^7.


http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?2008ASPC..398..167V&amp;data_type=PDF_H IGH&amp;whole_paper=YES&amp;type=PRINTER&amp;filetype=.pdf

Planets Surviving Stellar Evolution

Villaver, E.; Livio, M.

Over the last few years several groups have surveyed white dwarfs in the search for planets. The underlying assumption has been that planets can survive the parent star's evolution if they manage to stay in a large enough orbit to avoid engulfment by the star, when the latter increases its radius as it ascends the Red Giant Branch and Asymptotic Giant Branch (AGB). We have explored this hypothesis by determining: (1) the planet's survival during the AGB phase and the orbital changes due to the AGB mass-loss using the range of initial masses for white dwarfs progenitors, and (2) the range of parameters under which an outflow from the gas planet caused by irradiation by the planetary nebulae central star leads to the total destruction of the planet. We show that planets with masses less than one Jupiter mass do not survive the planetary nebula phase if located initially at orbital distances smaller than 3-5 AU. Planets more massive than two Jupiter masses around low-mass stars (1 Msun; on the Main Sequence) survive the planetary nebulae stage down to orbital distances of ˜3 AU. Planets around white dwarfs with masses of MWD > 0.7 Msun; are generally expected to be found at orbital radii r > 15 AU.


Recycling a PLANET? Well, actually, I guess so...


Exoplanet recycling in massive white-dwarf debris discs

Rik van Lieshout, Quentin Kral, Sébastien Charnoz, Mark C. Wyatt, Andrew Shannon
(Submitted on 11 May 2018)

Several tens of white dwarfs are known to host circumstellar discs of dusty debris, thought to arise from the tidal disruption of rocky bodies originating in the star's remnant planetary system. This paper investigates the evolution of such discs if they are very massive, as may be the case if their progenitor was a terrestrial planet, moon, or dwarf planet. Assuming the discs are physically thin and flat, like Saturn's rings, their evolution is governed by Poynting-Robertson drag or viscous spreading, where the disc's effective viscosity is due to self-gravity wakes. For discs with masses > 10^26 g, located in the outer parts of the tidal disruption zone, viscous spreading dominates the evolution, and mass is transported both in- and outwards. When outwards-spreading material flows beyond the Roche limit, it coagulates into new (minor) planets in a process analogous to the ongoing formation of moonlets at the outer edge of Saturn's rings. The newly formed bodies migrate outwards by exchanging angular momentum with the disc and coalesce into larger objects through mutual collisions. Eventually, the disc's Roche-limit overflow recycles tens of percent of the original disc mass; most ends up in a single large body near 2:1 mean-motion resonance with the disc's outer edge. Hence, the recycling of a tidally disrupted super-Earth, for example, could yield an Earth-mass planet on a ~10-h orbit, located in the habitable zone for 2-to-10-Gyr-old white dwarfs. The recycling process also creates a population of smaller bodies just outside the Roche limit, which may explain the minor planets recently postulated to orbit WD 1145+017.



WD1145+017 (Abstract)

Motta, M.

(Abstract only) WD1145 is a 17th magnitude white dwarf star 570 light years away in Virgo that was discovered to have a disintegrating planetoid in close orbit by Andrew Vanderburg, a graduate student at Harvard CfA, while data mining the elucidate the nature of its rather bizarre transit light curves. I obtained multiple observations of WD1145 over the course of a year, and found a series of complex transit light curves that could only be interpreted as a ring complex or torus in close orbit around WD1145. Combined with data from other amateur astronomers, professional observations, and satellite data, it became clear that WD1145 has a small planetoid in close orbit at the Roche limit and is breaking apart, forming a ring of debris material that is then raining down on the white dwarf. The surface of the star is "polluted" by heavy metals, determined by spectroscopic data. Given that in the intense gravitational field of a white dwarf any heavy metals could not for long last on the surface, this confirms that we are tracking in real time the destruction of a small planet by its host star.

Roger E. Moore
2018-Aug-21, 06:23 PM
Using what is probably a loose definition of a "disintegrating" planet, I count five of them. I was confused about one planet that had two names, shown here combined, and have added some links to catalog sources and Wikipedia (always useful for the links it provides, if not the information per page). Two additional articles as well. Enjoy.


KIC 12557548 b / Kepler-1520 b (thought these were different planets, my bad)

catalogs & wikis


Direct evidence for an evolving dust cloud from the exoplanet KIC 12557548 b
-------Jakub J. Bochinski, Carole A. Haswell, Tom R. Marsh, Vikram S. Dhillon, Stuart P. Littlefair (Submitted on 16 Feb 2015)
We present simultaneous multi-color optical photometry using ULTRACAM of the transiting exoplanet KIC 12557548 b (also known as KIC 1255 b). This reveals, for the first time, the color dependence of the transit depth. Our g and z transits are similar in shape to the average Kepler short-cadence profile, and constitute the highest-quality extant coverage of individual transits. Our Night 1 transit depths are 0.85 +/- 0.04% in z; 1.00 +/- 0.03% in g; and 1.1 +/- 0.3% in u. We employ a residual-permutation method to assess the impact of correlated noise on the depth difference between the z and g bands and calculate the significance of the color dependence at 3.2{\sigma}. The Night 1 depths are consistent with dust extinction as observed in the ISM, but require grain sizes comparable to the largest found in the ISM: 0.25-1{\mu}m. This provides direct evidence in favor of this object being a disrupting low-mass rocky planet, feeding a transiting dust cloud. On the remaining four nights of observations the object was in a rare shallow-transit phase. If the grain size in the transiting dust cloud changes as the transit depth changes, the extinction efficiency is expected to change in a wavelength- and composition-dependent way. Observing a change in the wavelength-dependent transit depth would offer an unprecedented opportunity to determine the composition of the disintegrating rocky body KIC 12557548 b. We detected four out-of-transit u band events consistent with stellar flares.


K2-22 b / EPIC 201637175 b

catalogs & wikis


------R. Sanchis-Ojeda, S. Rappaport, E. Pallè, L. Delrez, J. DeVore, D. Gandolfi, A. Fukui, I. Ribas, K. G. Stassun, S. Albrecht (Published 2015 October 14 The Astrophysical Journal
We present the discovery of a transiting exoplanet candidate in the K2 Field-1 with an orbital period of 9.1457 hr: K2-22b. The highly variable transit depths, ranging from ~0% to 1.3%, are suggestive of a planet that is disintegrating via the emission of dusty effluents. We characterize the host star as an M-dwarf with Teff sime 3800 K. We have obtained ground-based transit measurements with several 1-m class telescopes and with the GTC. These observations (1) improve the transit ephemeris; (2) confirm the variable nature of the transit depths; (3) indicate variations in the transit shapes; and (4) demonstrate clearly that at least on one occasion the transit depths were significantly wavelength dependent. The latter three effects tend to indicate extinction of starlight by dust rather than by any combination of solid bodies. The K2 observations yield a folded light curve with lower time resolution but with substantially better statistical precision compared with the ground-based observations. We detect a significant "bump" just after the transit egress, and a less significant bump just prior to transit ingress. We interpret these bumps in the context of a planet that is not only likely streaming a dust tail behind it, but also has a more prominent leading dust trail that precedes it. This effect is modeled in terms of dust grains that can escape to beyond the planet's Hill sphere and effectively undergo "Roche lobe overflow," even though the planet's surface is likely underfilling its Roche lobe by a factor of 2.


WD 1145+017 b

catalogs & wikis


KOI 2700 b / KIC 8639908 b

catalogs & wikis


KELT-9b / HD 195689 b

catalogs & wikis


KELT-9b: A Case Study in Dynamical Planet Ingestion by a Hot Host Star

Collins, Karen A.; Stassun, Keivan; Gaudi, B. Scott; Beatty, Thomas G.; Zhou, George; Latham, David W.; Bieryla, Allyson; Eastman, Jason D.; Siverd, Robert; Crepp, Justin R.; Pepper, Joshua

Nearly all of the known transiting extra-solar planets orbit stars with masses similar to, or less massive than, the Sun. Such stars typically do not evolve substantially over their hydrogen-fusion lifetime of roughly 10 billion years or more. In contrast, stars much more massive than the Sun evolve on much shorter timescales, and thus the planets they host represent important test cases for how such systems evolve as their parent stars expand -- perhaps engulfing their planets. Most planetary systems orbiting such massive stars have been found around stars that have already exhausted their core hydrogen, cooled, swelled, and likely erased the knowledge of their progenitor close-in planetary systems. In contrast, KELT-9b is a "hot Jupiter" orbiting a star with a mass of 2.2 Msun. The star is still unevolved and therefore still very hot (surface temperature ~ 10,000 K) and therefore the planet is extremely hot. The planet is on a near-polar orbit, likely resulting in orbital precession that will be detectable within a few years. Given the extreme planet temperature, large planet-to-star radius ratio, large planetary atmospheric scale height, and short orbital period, this system is an exceptionally good target for follow-up studies of the planet's atmosphere, which may exhibit unusual photochemistry due to the extreme amounts of high-energy radiation it receives.



Atomic iron and titanium in the atmosphere of the exoplanet KELT-9b

H. Jens Hoeijmakers, David Ehrenreich, Kevin Heng, Daniel Kitzmann, Simon L. Grimm, Romain Allart, Russell Deitrick, Aurelien Wyttenbach, Maria Oreshenko, Lorenzo Pino, Paul B. Rimmer, Emilio Molinari, Luca Di Fabrizio5
16 Aug 2018

The chemical composition of an exoplanet is a key ingredient in constraining its formation history [1, 2, 3]. Iron is the most abundant transition metal, but has never been directly detected in an exoplanet due to its highly refractory nature. KELT-9b (HD 195689b) is the archetype of the class of ultra-hot Jupiters that straddle the transition between stars and gas-giant exoplanets and serve as distinctive laboratories for studying atmospheric chemistry, because of its high equilibrium temperature of 4050 ± 180 K [4]. These properties imply that its atmosphere is a tightly constrained chemical system that is expected to be nearly in chemical equilibrium [5] and cloud-free [6, 7]. It was previously predicted that the spectral lines of iron will be detectable in the visible range of wavelengths [5]. At these high temperatures, iron and several other transition metals are not sequestered in molecules or cloud particles and exist solely in their atomic forms [5]. Here, we report the direct detection of atomic neutral and singly-ionized iron (Fe and Fe+), and singly-ionized titanium (Ti+) in KELT-9b via the cross-correlation technique [8] applied to high-resolution spectra obtained during the primary transit of the exoplanet.

Roger E. Moore
2018-Aug-22, 02:12 AM
new paper...


Inferring the Composition of Disintegrating Planet Interiors from Dust Tails with Future James Webb Space Telescope Observations

Eva H. L. Bodman, Jason T. Wright, Steven J. Desch, Carey M. Lisse
(Submitted on 21 Aug 2018)

Disintegrating planets allow for the unique opportunity to study the composition of the interiors of small, hot, rocky exoplanets because the interior is evaporating and that material is condensing into dust, which is being blown away and then transiting the star. Their transit signal is dominated by dusty effluents forming a comet-like tail trailing the host planet (or leading it, in the case of K2-22b), making these good candidates for transmission spectroscopy. To assess the ability of such observations to diagnose the dust composition, we simulate the transmission spectra from 5-14 μm for the planet tail assuming an optically-thin dust cloud comprising a single dust species with a constant column density scaled to yield a chosen visible transit depth. We find that silicate resonant features near 10 μm can produce transit depths that are at least as large as those in the visible. For the average transit depth of 0.55% in the Kepler band for K2-22b, the features in the transmission spectra can be as large as 1%, which is detectable with the JWST MIRI low-resolution spectrograph in a single transit. The detectability of compositional features is easier with an average grain size of 1 μm despite features being more prominent with smaller grain sizes. We find most features are still detectable for transit depths of ~0.3% in the visible range. If more disintegrating planets are found with future missions such as the space telescope TESS, follow-up observations with JWST can explore the range of planetary compositions.

Roger E. Moore
2018-Aug-23, 01:13 AM

Fast spectrophotometry of WD 1145+017

P. Izquierdo (IAC/ULL), P. Rodríguez-Gil (IAC/ULL), B. T. Gänsicke (Warwick), A. J. Mustill (Lund Obs.), O. Toloza (Warwick), P. E. Tremblay (Warwick), M. Wyatt (IoA, Cambridge), P. Chote (Warwick), S. Eggl (JPL), J. Farihi (UCL, London), D. Koester (Kiel), W. Lyra (JPL/CSU), C. J. Manser (Warwick), T. R. Marsh (Warwick), E. Pallé (IAC/ULL), R. Raddi (Karl Remeis-Sternwarte), D. Veras (Warwick), E. Villaver (UAM, Madrid), S. Portegies Zwart (Leiden)
(Submitted on 22 Aug 2018)

WD 1145+017 is currently the only white dwarf known to exhibit periodic transits of planetary debris as well as absorption lines from circumstellar gas. We present the first simultaneous fast optical spectrophotometry and broad-band photometry of the system, obtained with the Gran Telescopio Canarias (GTC) and the Liverpool Telescope (LT), respectively. The observations spanned 5.5h, somewhat longer than the 4.5-h orbital period of the debris. Dividing the GTC spectrophotometry into five wavelength bands reveals no significant colour differences, confirming grey transits in the optical. We argue that absorption by an optically thick structure is a plausible alternative explanation for the achromatic nature of the transits that can allow the presence of small-sized (∼μm) particles. The longest (87 min) and deepest (50 per cent attenuation) transit recorded in our data exhibits a complex structure around minimum light that can be well modelled by multiple overlapping dust clouds. The strongest circumstellar absorption line, Fe II λ5169, significantly weakens during this transit, with its equivalent width reducing from a mean out-of-transit value of 2\AA\ to 1\AA\ in-transit, supporting spatial correlation between the circumstellar gas and dust. Finally, we made use of the Gaia Data Release 2 and archival photometry to determine the white dwarf parameters. Adopting a helium-dominated atmosphere containing traces of hydrogen and metals, and a reddening E(B−V)=0.01 we find Teff = 15020 ± 520K, logg = 8.07 ± 0.07, corresponding to MWD = 0.63±0.05 M⊙ and a cooling age of 224 ± 30 Myr.

Roger E. Moore
2018-Aug-28, 01:54 PM
Possibly another disintegrating planet or planets, this time around RW Aurigae...


Optical dimming of RW Aur associated with an iron rich corona and exceptionally high absorbing column density

Hans Moritz Günther, T. Birnstiel, D. P. Huenemoerder, D. A. Principe, P. C. Schneider, S. J. Wolk, Franky Dubois, Ludwig Logie, Steve Rau, Sigfried Vanaverbeke
(Submitted on 18 Jul 2018)

RW Aur is a binary system composed of two young, low-mass stars. The primary, RW Aur A, has undergone visual dimming events (ΔV=2−3 ~mag) in 2011, 2014-16, and 2017-2018. Visual and IR observations indicate a gray absorber that moved into the line-of-sight. This dimming is also associated with changes in the outflow. In 2017, when the optical brightness was almost 2~mag below the long-term average we triggered a Chandra observation to measure the absorbing column density N H and to constrain dust properties and the gas-to-dust ratio of the absorber. In 2017, the X-ray spectrum is more absorbed than it was in the optically bright state (N H =(4±1)×10 23 cm −2 ) and shows significantly more hot plasma than in X-ray observations taken before. Also, a new emission feature at 6.63±0.02 keV (statistic) ±0.02 keV (systematic) appeared indicating an Fe abundance an order of magnitude above Solar, in contrast with previous sub-Solar Fe abundance measurements. Comparing X-ray absorbing column density NH and optical extinction AV, we find that either the gas-to-dust ratio in the absorber is orders of magnitude higher than in the ISM or the absorber has undergone significant dust evolution. Given the high column density coupled with changes in the X-ray spectral shape, this absorber is probably located in the inner disk. We speculate that a break-up of planetesimals or a terrestrial planet could supply large grains causing gray absorption; some of these grains would be accreted and enrich the stellar corona with iron which could explain the inferred high abundance.

Roger E. Moore
2018-Aug-31, 12:19 PM
This seems to qualify. RE-REVISED version of fascinating article.


A-type Stars, the Destroyers of Worlds: The lives and deaths of Jupiters in evolving stellar binaries

Alexander P. Stephan, Smadar Naoz, B. Scott Gaudi
(Submitted on 11 Jun 2018 (v1), last revised 30 Jul 2018 (this version, v3))

Hot Jupiters (HJs), gas giant planets orbiting their host stars with periods on the order of days, commonly occur in the Galaxy, including relatively massive (1.6−2.4 M⊙, i.e., A-type main sequence stars) and evolved stars. The majority of A-type main sequence stars have stellar binary companions, which can strongly affect the dynamical evolution of planets around either star. In this work, we investigate the effects of gravitational perturbations by a far away stellar companion on the orbital evolution of gas giant planets orbiting A-type stars, the so-called Eccentric Kozai-Lidov (EKL) mechanism, including the effects of general relativity, post-main sequence stellar evolution, and tides. We find that only 0.15% of A-type stars will host HJs during their main sequence lifetime. However, we also find a new class of planets, Temporary Hot Jupiters (THJs), that form during the post-main sequence lifetime of about 3.7% of former A-type main sequence stars. These THJs orbit on periods of tens to a hundred days and only exist for a few 100,000 years before they are engulfed, but they reach similar temperatures as `classical' HJs due to the increased stellar luminosities. THJs' spin-orbit angles will mostly be misaligned. THJ effects on the host stars' evolution could also be observable for longer than a few 100,000 years. Overall, we find that approximately 70% of all gas giant planets orbiting A-type stars will eventually be destroyed or engulfed by their star, about 25% during the main sequence lifetime, about 45% during post-main sequence evolution.

Roger E. Moore
2018-Sep-04, 03:03 PM
Older papers on Jovian planets which appear to be close to gravitational tidal disruption. WASP-103 b, WASP-121 b, and KELT-16 b, and one on asteroid-eater white dwarf SDSS J0845+2257 (Ton 345)



WASP-103b: a new planet at the edge of tidal disruption

M. Gillon, D. R. Anderson, A. Collier-Cameron, L. Delrez, C. Hellier, E. Jehin, M. Lendl, P. F. L. Maxted, F. Pepe, D. Pollacco, D. Queloz, D. Segransan, A. M. S. Smith, B. Smalley, J. Southworth, A. H. M. J. Triaud, S. Udry, V. Van Grootel, R. G. West
(Submitted on 13 Jan 2014)

We report the discovery of WASP-103b, a new ultra-short-period planet (P=22.2 hr) transiting a 12.1 V-magnitude F8-type main-sequence star (1.22 +-0.04 Msun, 1.44 -0.03/+0.05 Rsun, Teff = 6110 +-160 K). WASP-103b is significantly more massive (1.49 +-0.09 Mjup) and larger (1.53 -0.07/+0.05 Rjup) than Jupiter. Its large size and extreme irradiation (around 9 x 10^9 erg/s/cm^2) make it an exquisite target for a thorough atmospheric characterization with existing facilities. Furthermore, its orbital distance is less than 20% larger than its Roche radius, meaning that it might be significantly distorted by tides and might experience mass loss through Roche-lobe overflow. It thus represents a new key object for understanding the last stage of the tidal evolution of hot Jupiters.



KELT-16b: A highly irradiated, ultra-short period hot Jupiter nearing tidal disruption

Thomas E. Oberst, Joseph E. Rodriguez, Knicole D. Colón, Daniel Angerhausen, Allyson Bieryla, Henry Ngo, Daniel J. Stevens, Keivan G. Stassun, B. Scott Gaudi, Joshua Pepper, Kaloyan Penev, Dimitri Mawet, David W. Latham, Tyler M. Heintz, Baffour W. Osei, Karen A. Collins, John F. Kielkopf, Tiffany Visgaitis, Phillip A. Reed, Alejandra Escamilla, Sormeh Yazdi, Kim K. McLeod, Leanne T. Lunsford, Michelle Spencer, Michael D. Joner, Joao Gregorio, Clement Gaillard, Kyle Matt, Mary Thea Dumont, Denise C. Stephens, David H. Cohen, Eric L. N. Jensen, Sebastiano Calchi Novati, Valerio Bozza, Jonathan Labadie-Bartz, Robert J. Siverd, Michael B. Lund, Thomas G. Beatty, Jason D. Eastman, Matthew T. Penny, Mark Manner, Roberto Zambelli, Benjamin J. Fulton, Christopher Stockdale, D. L. DePoy, Jennifer L. Marshall, et al. (4 additional authors not shown)
(Submitted on 1 Aug 2016 (v1), last revised 31 Jan 2017 (this version, v2))

We announce the discovery of KELT-16b, a highly irradiated, ultra-short period hot Jupiter transiting the relatively bright (V=11.7) star TYC 2688-1839-1. A global analysis of the system shows KELT-16 to be an F7V star with T eff = 6236 ±54 K, logg ⋆ = 4.253 +0.031/−0.036, [Fe/H] = -0.002 +0.086/−0.085, M ⋆ = 1.211 +0.043/−0.046 M⊙, and R ⋆ = 1.360 +0.064/−0.053 R⊙. The planet is a relatively high mass inflated gas giant with M P = 2.75 +0.16/−0.15 M J, R P = 1.415 +0.084/−0.067 R J, density ρ P = 1.20±0.18 g cm −3, surface gravity logg P = 3.530 +0.042/−0.049, and T eq = 2453 +55/−47 K. The best-fitting linear ephemeris is T C = 2457247.24791 ±0.00019 BJD tdb and P = 0.9689951 ±0.0000024 d. KELT-16b joins WASP-18b, -19b, -43b, -103b, and HATS-18b as the only giant transiting planets with P<1 day. Its ultra-short period and high irradiation make it a benchmark target for atmospheric studies by HST, Spitzer, and eventually JWST. For example, as a hotter, higher mass analog of WASP-43b, KELT-16b may feature an atmospheric temperature-pressure inversion and day-to-night temperature swing extreme enough for TiO to rain out at the terminator. KELT-16b could also join WASP-43b in extending tests of the observed mass-metallicity relation of the Solar System gas giants to higher masses. KELT-16b currently orbits at a mere ∼ 1.7 Roche radii from its host star, and could be tidally disrupted in as little as a few ×10^5 years (for a stellar tidal quality factor of Q ′ ∗ =10^5). Finally, the likely existence of a widely separated bound stellar companion in the KELT-16 system makes it possible that Kozai-Lidov oscillations played a role in driving KELT-16b inward to its current precarious orbit.



Planetary engulfment as a trigger for white dwarf pollution

Cristobal Petrovich, Diego J. Muñoz
(Submitted on 17 Jul 2016 (v1), last revised 21 Oct 2016 (this version, v2))

The presence of a planetary system can shield a planetesimal disk from the secular gravitational perturbations due to distant outer massive objects (planets or stellar companions). As the host star evolves off the main sequence to become a white dwarf, these planets can be engulfed, triggering secular instabilities and leading to the tidal disruptions of small rocky bodies. These disrupted bodies can feed the white dwarfs with rocky material and possibly explain the high-metallicity material in their atmospheres. We illustrate how this mechanism can operate when the gravitational perturbations are due to the Kozai-Lidov mechanism from a stellar binary companion. We show that this mechanism can explain the observed levels of accretion if: (1) the planetary engulfment happens fast compared to the secular timescale, which is generally the case for wide binaries (>100 AU) and planetary engulfment during the Asymptotic Giant Branch; (2) the planetesimal disk has a total mass of ∼10 −4 −10 −2 M ⊕. We show that this new mechanism can provide a steady supply of material throughout the entire life of the white dwarfs for all cooling ages and can account for a large fraction (up to nearly half) of the observed polluted WDs.



WASP-121 b: a hot Jupiter in a polar orbit and close to tidal disruption

L. Delrez, A. Santerne, J.-M. Almenara, D. R. Anderson, A. Collier-Cameron, R. F. Díaz, M. Gillon, C. Hellier, E. Jehin, M. Lendl, P. F. L. Maxted, M. Neveu-VanMalle, F. Pepe, D. Pollacco, D. Queloz, D. Ségransan, B. Smalley, A. M. S. Smith, A. H. M. J. Triaud, S. Udry, V. Van Grootel, R. G. West
(Submitted on 8 Jun 2015)

We present the discovery by the WASP-South survey, in close collaboration with the Euler and TRAPPIST telescopes, of WASP-121 b, a new remarkable short-period transiting hot Jupiter, whose planetary nature has been statistically validated by the PASTIS software. The planet has a mass of 1.183 +0.064/−0.062 M Jup, a radius of 1.865 ± 0.044 R Jup, and transits every 1.2749255 +0.0000020/−0.0000025 days an active F6-type main-sequence star (V =10.4, 1.353 +0.080/−0.079 M⊙, 1.458 ± 0.030 R⊙, T eff = 6460 ± 140 K). A notable property of WASP-121 b is that its orbital semi-major axis is only ∼ 1.15 times larger than its Roche limit, which suggests that the planet might be close to tidal disruption. Furthermore, its large size and extreme irradiation (∼ 7.110 9 erg s −1 cm −2) make it an excellent target for atmospheric studies via secondary eclipse observations. Using the TRAPPIST telescope, we indeed detect its emission in the z ′ -band at better than ∼ 4σ, the measured occultation depth being 603 ± 130 ppm. Finally, from a measurement of the Rossiter-McLaughlin effect with the CORALIE spectrograph, we infer a sky-projected spin-orbit angle of 257.8 +5.3/−5.5 deg. This result indicates a significant misalignment between the spin axis of the host star and the orbital plane of the planet, the planet being in a nearly polar orbit. Such a high misalignment suggests a migration of the planet involving strong dynamical events with a third body.



The Composition Of A Disrupted Extrasolar Planetesimal At SDSS J0845+2257 (Ton 345)

David J. Wilson, Boris T. Gaensicke, Detlev Koester, Odette Toloza, Anna F. Pala, Elmé Breedt, Steven G. Parsons
(Submitted on 27 May 2015 (v1), last revised 31 May 2015 (this version, v2))

We present a detailed study of the metal-polluted DB white dwarf SDSS J0845+2257 (Ton 345). Using high-resolution HST/COS and VLT spectroscopy, we have detected hydrogen and eleven metals in the atmosphere of the white dwarf. The origin of these metals is almost certainly the circumstellar disc of dusty and gaseous debris from a tidally-disrupted planetesimal, accreting at a rate of 1.6E10 gs^-1. Studying the chemical abundances of the accreted material demonstrates that the planetesimal had a composition similar to the Earth, dominated by rocky silicates and metallic iron, with a low water content. The mass of metals within the convection zone of the white dwarf corresponds to an asteroid of at least ~130-170 km in diameter, although the presence of ongoing accretion from the debris disc implies that the planetesimal was probably larger than this. While a previous abundance study of the accreted material has shown an anomalously high mass fraction of carbon (15 percent) compared to the bulk Earth, our independent analysis results in a carbon abundance of just 2.5 percent. Enhanced abundances of core material (Fe, Ni) suggest that the accreted object may have lost a portion of its mantle, possibly due to stellar wind stripping in the asymptotic giant branch. Time-series spectroscopy reveals variable emission from the orbiting gaseous disc, demonstrating that the evolved planetary system at SDSS J0845+2257 is dynamically active.

Roger E. Moore
2018-Sep-04, 03:25 PM
Additional articles on WASP-103 b, WASP-121 b, and KELT-16 b



A Planet Soon to Meet Its Demise [[KELT-16b news report--REM]]

Kohler, Susanna



Follow-Up Photometry of Kelt Transiting Planet Candidates [[KELT-9b & KELT-16b--REM]]

Stephens, Denise C.; Joner, Michael D.; Hintz, Eric G.; Martin, Trevor; Spencer, Alex; Kelt Follow-Up Network (FUN) Team

We have three telescopes at BYU that we use to follow-up possible transiting planet canidates for the KELT team. These telescopes were used to collect data on Kelt-16b and Kelt-9b, which is the hottest known exoplanet. More recently we used the newest of these telescopes, a robotic 8-inch telescope on the roof of our building, to confirm the most recent Kelt planet that will be published soon. This research has been ideal for the teaching and training of undergraduate students in the art of photometric observing and data reduction. In this presentation I will highlight how we are using our membership in the Kelt team to further the educational objective of our undergraduate astronomy program, while contributing meaningful science to the ever growing field of exoplanet discovery. I will also highlight a few of the more interesting Kelt planets and the minimum telescope requirements for detecting these planets. I will then discuss the sensitivities required to follow-up future TESS candidates, which may be of interest to others interested in joining the TESS follow-up teams.



Global Climate and Atmospheric Composition of the Ultra-Hot Jupiter WASP-103b from HST and Spitzer Phase Curve Observations

Laura Kreidberg, Michael R. Line, Vivien Parmentier, Kevin B. Stevenson, Tom Louden, Mickäel Bonnefoy, Jacqueline K. Faherty, Gregory W. Henry, Michael H. Williamson, Keivan Stassun, Jacob L. Bean, Jonathan J. Fortney, Adam P. Showman, Jean-Michel Désert, Jacob Arcangeli
(Submitted on 30 Apr 2018 (v1), last revised 6 Jun 2018 (this version, v2))

We present thermal phase curve measurements for the hot Jupiter WASP-103b observed with Hubble/WFC3 and Spitzer/IRAC. The phase curves have large amplitudes and negligible hotspot offsets, indicative of poor heat redistribution to the nightside. We fit the phase variation with a range of climate maps and find that a spherical harmonics model generally provides the best fit. The phase-resolved spectra are consistent with blackbodies in the WFC3 bandpass, with brightness temperatures ranging from 1880±40 K on the nightside to 2930±40 K on the dayside. The dayside spectrum has a significantly higher brightness temperature in the Spitzer bands, likely due to CO emission and a thermal inversion. The inversion is not present on the nightside. We retrieved the atmospheric composition and found the composition is moderately metal-enriched ([M/H]=23 +29/−13 × solar) and the carbon-to-oxygen ratio is below 0.9 at 3σ confidence. In contrast to cooler hot Jupiters, we do not detect spectral features from water, which we attribute to partial H2O dissociation. We compare the phase curves to 3D general circulation models and find magnetic drag effects are needed to match the data. We also compare the WASP-103b spectra to brown dwarfs and young directly imaged companions and find these objects have significantly larger water features, indicating that surface gravity and irradiation environment play an important role in shaping the spectra of hot Jupiters. These results highlight the 3D structure of exoplanet atmospheres and illustrate the importance of phase curve observations for understanding their complex chemistry and physics.



Signs of strong Na and K absorption in the transmission spectrum of WASP-103b

M. Lendl, P.E. Cubillos, J. Hagelberg, A. Müller, I. Juvan, L. Fossati
(Submitted on 18 Aug 2017)

Context: Transmission spectroscopy has become a prominent tool for characterizing the atmospheric properties on close-in transiting planets. Recent observations have revealed a remarkable diversity in exoplanet spectra, which show absorption signatures of Na, K and H 2 O, in some cases partially or fully attenuated by atmospheric aerosols. Aerosols (clouds and hazes) themselves have been detected in the transmission spectra of several planets thanks to wavelength-dependent slopes caused by the particles' scattering properties. Aims: We present an optical 550 - 960 nm transmission spectrum of the extremely irradiated hot Jupiter WASP-103b, one of the hottest (2500 K) and most massive (1.5 M J) planets yet to be studied with this technique. WASP-103b orbits its star at a separation of less than 1.2 times the Roche limit and is predicted to be strongly tidally distorted. Methods: We have used Gemini/GMOS to obtain multi-object spectroscopy hroughout three transits of WASP-103b. We used relative spectrophotometry and bin sizes between 20 and 2 nm to infer the planet's transmission spectrum. Results: We find that WASP-103b shows increased absorption in the cores of the alkali (Na, K) line features. We do not confirm the presence of any strong scattering slope as previously suggested, pointing towards a clear atmosphere for the highly irradiated, massive exoplanet WASP-103b. We constrain the upper boundary of any potential cloud deck to reside at pressure levels above 0.01 bar. This finding is in line with previous studies on cloud occurrence on exoplanets which find that clouds dominate the transmission spectra of cool, low surface gravity planets while hot, high surface gravity planets are either cloud-free, or possess clouds located below the altitudes probed by transmission spectra.



Spin-orbit alignments for Three Transiting Hot Jupiters: WASP-103b, WASP-87b, & WASP-66b

B. C. Addison, C. G. Tinney, D. J. Wright, D. Bayliss
(Submitted on 18 Mar 2016 (v1), last revised 23 May 2016 (this version, v2))

We have measured the sky-projected spin-orbit alignments for three transiting Hot Jupiters, WASP-103b, WASP-87b, and WASP-66b, using spectroscopic measurements of the Rossiter-McLaughlin effect, with the CYCLOPS2 optical-fiber bundle system feeding the UCLES spectrograph on the Anglo-Australian Telescope. The resulting sky projected spin-orbit angles of λ=3 ∘ ±33 ∘, λ=−8 ∘ ±11 ∘, and λ=−4 ∘ ±22 ∘ for WASP-103b, WASP-87b, and WASP-66b, respectively, suggest that these three planets are likely on nearly aligned orbits with respect to their host star's spin axis. WASP-103 is a particularly interesting system as its orbital distance is only 20% larger than its host star's Roche radius and the planet likely experiences strong tidal effects. WASP-87 and WASP-66 are hot (T eff =6450±120 K and T eff =6600±150 K, respectively) mid-F stars making them similar to the majority of stars hosting planets on high obliquity orbits. Moderate spin-orbit misalignments for WASP-103b and WASP-66b are consistent with our data, but polar and retrograde orbits are not favored for these systems.



Characterizing an extreme planet on the verge of tidal disruption

Evans, Thomas

We propose to use WFC3 G141 to observe a transit of the recently discovered hot gas giant WASP-121b, the latest exoplanet that is ideally suited for atmospheric characterization. With an equilibrium temperature well above 2000K and an inflated radius of nearly 2 Jupiter radii, the predicted transmission signal is the largest of all known exoplanets in this temperature regime. Our transmission observations will provide detailed insight into the atmosphere of this extreme world, which sits in a polar orbit just beyond the Roche limit and is likely to be undergoing tidal disruption. We will measure the water absorption feature centered at 1.4 micron at high signal-to-noise, and use this information to determine fundamental properties of the atmosphere, including whether WASP-121b is clear or cloudy. The proposed observations will also be sensitive to absorption by TiO/VO, which is expected to be in the gas phase. A detection/non-detection of TiO/VO would be significant, providing valuable constraints on the chemisty and circulation of hot Jupiters. Being one of the most favorable targets known for both transmission and emission spectroscopy, it is anticipated that WASP-121b will be intensely studied by HST in the future. The information gleaned from the single transit observation proposed here will allow observing strategies to be optimized in time for the HST Cycle 24 proposal round.



An Observational Diagnostic for Distinguishing Between Clouds and Haze in Hot Exoplanet Atmospheres

Kempton, Eliza; Bean, Jacob; Parmentier, Vivien

The nature of aerosols in hot exoplanet atmospheres is one of the primary vexing questions facing the exoplanet field. The complex chemistry, multiple formation pathways, and lack of easily identifiable spectral features associated with aerosols make it especially challenging to constrain their key properties. We present a transmission spectroscopy technique to identify the primary aerosol formation mechanism for the most highly irradiated hot Jupiters (HIHJs). The technique is based on the idea that the two key types of aerosols -- photochemically generated hazes and equilibrium condensate clouds -- are expected to form and persist in different regions of a highly irradiated planet's atmosphere. Haze can only be produced on the permanent daysides of tidally-locked hot Jupiters, and will be carried downwind by atmospheric dynamics to the evening terminator (seen as the trailing limb during transit). Clouds can only form in cooler regions on the night side and morning terminator of HIHJs (seen as the leading limb during transit). Because opposite limbs are expected to be impacted by different types of aerosols, ingress and egress spectra, which primarily probe opposing sides of the planet, will reveal the dominant aerosol formation mechanism. We show that the benchmark HIHJ, WASP-121b, has a transmission spectrum consistent with partial aerosol coverage and that ingress-egress spectroscopy would constrain the location and formation mechanism of those aerosols. In general, we find that observations with JWST and potentially with HST should be able to distinguish between clouds and haze for currently known HIHJs.

Roger E. Moore
2018-Sep-04, 03:26 PM
Articles on the asteroid-eating WD, SDSS J0845+2257 (perhaps better known as Ton 345)



Evidence for an Anhydrous Carbonaceous Extrasolar Minor Planet

M. Jura, P. Dufour, S. Xu, B. Zuckerman, B. Klein, E. D. Young, C. Melis
(Submitted on 18 Nov 2014)

Using Keck/HIRES, we report abundances of 11 different elements heavier than helium in the spectrum of Ton 345, a white dwarf that has accreted one of its own minor planets. This particular extrasolar planetesimal which was at least 60% as massive as Vesta appears to have been carbon-rich and water-poor; we suggest it was compositionally similar to those Kuiper Belt Objects with relatively little ice.



Non-LTE spectral models for the gaseous debris-disk component of Ton 345

S. Hartmann, T. Nagel, T. Rauch, K. Werner
(Submitted on 5 Nov 2014)

For a fraction of single white dwarfs with debris disks, an additional gaseous disk was discovered. Both dust and gas are thought to be created by the disruption of planetary bodies. The composition of the extrasolar planetary material can directly be analyzed in the gaseous disk component, and the disk dynamics might be accessible by investigating the temporal behavior of the Ca II infrared emission triplet, hallmark of the gas disk. We obtained new optical spectra for the first helium-dominated white dwarf for which a gas disk was discovered (Ton 345) and modeled the non-LTE spectra of viscous gas disks composed of carbon, oxygen, magnesium, silicon, sulfur, and calcium with chemical abundances typical for solar system asteroids. Iron and its possible line-blanketing effects on the model structure and spectral energy distribution was still neglected. A set of models with different radii, effective temperatures, and surface densities as well as chondritic and bulk-Earth abundances was computed and compared with the observed line profiles of the Ca II infrared triplet. Our models suggest that the Ca II emission stems from a rather narrow gas ring with a radial extent of R=0.44-0.94 Rsol, a uniform surface density Sigma=0.3 g/cm2, and an effective temperature of Teff=6000 K. The often assumed chemical mixtures derived from photospheric abundances in polluted white dwarfs - similar to a chondritic or bulk-Earth composition - produce unobserved emission lines in the model and therefore have to be altered. We do not detect any line-profile variability on timescales of hours, but we confirm the long-term trend over the past decade for the red-blue asymmetry of the double-peaked lines.

Roger E. Moore
2018-Sep-20, 12:45 PM
While technically there are just three "disintegrating" planets, per below, other planets have been found that are being torn apart by intense radiation and other forces. Just-out paper below has details on one closely followed world.


A Large Ground-Based Observing Campaign of the Disintegrating Planet K2-22b

Knicole D. Colón, et al. (Submitted on 19 Sep 2018)

ABSTRACT: "We present 45 ground-based photometric observations of the K2-22 system collected between December 2016 and May 2017, which we use to investigate the evolution of the transit of the disintegrating planet K2-22b. Last observed in early 2015, in these new observations we recover the transit at multiple epochs and measure a typical depth of <1.5%. We find that the distribution of our measured transit depths is comparable to the range of depths measured in observations from 2014 and 2015. These new observations also support ongoing variability in the K2-22b transit shape and time, although the overall shallowness of the transit makes a detailed analysis of these transit parameters difficult. We find no strong evidence of wavelength-dependent transit depths for epochs where we have simultaneous coverage at multiple wavelengths, although our stacked Las Cumbres Observatory data collected over days-to-months timescales are suggestive of a deeper transit at blue wavelengths. We encourage continued high-precision photometric and spectroscopic monitoring of this system in order to further constrain the evolution timescale and to aid comparative studies with the other few known disintegrating planets."

QUOTES: "At present, there are only three such [[disintegrating]] planets known around main-sequence stars: KIC 12557548b (Rappaport et al. 2012), KOI-2700b (Rappaport et al. 2014), and K2-22b (Sanchis-Ojeda et al. 2015).... Because such objects are rare, the systems named above have been under intense study so as to better understand their formation and evolution. In particular, observations over long timescales can be used to determine the rate at which the transit depth evolves over time. In addition, multi-wavelength observations can provide constraints on the properties of the grains that are present in the dust tails. For example, several such studies have been done for WD 1145+017 (Vanderburg et al. 2015; Vanderburg & Rappaport 2018), which is a white dwarf star that has disintegrating planetesimals in orbit around it and is perhaps the most well-studied "disintegrating" system to date (e.g., Alonso et al. 2016; Gansicke et al. 2016; Zhou et al. 2016; Croll et al. 2017; Hallakoun et al. 2017; Red eld et al. 2017; Vanderburg & Rappaport 2018; Xu et al. 2018). However, because this system consists of debris orbiting a post-main-sequence star, it is arguably in a different class than the other three disintegrating planets known."

"The planet K2-22b orbits an M-dwarf with a period of just 9 hr (Sanchis-Ojeda et al. 2015), much shorter than the two aforementioned disintegrating planets.... A wavelength dependent transit light curve shape was also measured during one particularly deep transit, supporting dust scattering during the transit. Another significant difference between K2-22b and both KIC 12557548b and KOI-2700b is that K2-22b appears to have both a leading and trailing dust tail, rather than just a trailing one."

"A comprehensive overview and comparison of the three known disintegrating planets around main-sequence stars was provided in van Lieshout & Rappaport (2017), and the data presented here further supports the fact that all disintegrating planets seem to display variable transit depths on all timescales observed, from transit to transit to several years."

Roger E. Moore
2018-Sep-20, 02:16 PM
An effective way to destroy a planet is to "trip" it in its orbit, sending it right into its sun to either be broken apart at the Roche limit (forming a debris disk) or absorbed by the star. The orbital "tripping" can be accomplished by other planets.


White Dwarf Pollution by Asteroids from Secular Resonances

Jeremy L. Smallwood, Rebecca G. Martin, Mario Livio, Stephen H. Lubow (Submitted on 7 Jul 2018)

In the past few decades, observations have revealed signatures of metals polluting the atmospheres of white dwarfs. The diffusion timescale for metals to sink from the atmosphere of a white dwarf is of the order of days for a hydrogen-dominated atmosphere. Thus, there must be a continuous supply of metal-rich material accreting onto these white dwarfs. We investigate the role of secular resonances that excite the eccentricity of asteroids allowing them to reach star-grazing orbits leading them to tidal disruption and the formation of a debris disc. Changes in the planetary system during the evolution of the star lead to a change in the location of secular resonances. In our Solar System, the engulfment of the Earth will cause the ν6 resonance to shift outwards which will force previously stable asteroids to undergo secular resonant perturbations. With analytic models and N-body simulations we show that secular resonances driven by two outer companions can provide a source of continuous pollution. Secular resonances are a viable mechanism for the pollution of white dwarfs in a variety of exoplanetary system architectures.

Roger E. Moore
2018-Oct-07, 02:28 PM
No new news, but...


A marvelous artwork showing the disintegrating exoplanet around KIC 12557548. Also...


… a JPL infographic identifying details of the scene. Thought it was worth showing.

Roger E. Moore
2018-Oct-11, 01:35 AM
More news on that white dwarf that's eating planets, which yes I know a lot of them do.


Time resolved spectroscopy of dust and gas from extrasolar planetesimals orbiting WD 1145+017

Marie Karjalainen, et al. (Submitted on 10 Oct 2018)

Multiple long and variable transits caused by dust from possibly disintegrating asteroids were detected in light curves of WD 1145+017. We present time-resolved spectroscopic observations of this target with QUCAM CCDs mounted in the Intermediate dispersion Spectrograph and Imaging System at the 4.2-m William Herschel Telescope in two different spectral arms: the blue arm covering 3800-4025 {\AA} and the red arm covering 7000-7430 {\AA}. When comparing individual transits in both arms, our observations show with 20 {\sigma} significance an evident colour difference between the in- and out-of-transit data of the order of 0.05-0.1 mag, where transits are deeper in the red arm. We also show with > 6 {\sigma} significance that spectral lines in the blue arm are shallower during transits than out-of-transit. For the circumstellar lines it also appears that during transits the reduction in absorption is larger on the red side of the spectral profiles. Our results confirm previous findings showing the u'-band excess and a decrease in line absorption during transits. Both can be explained by an opaque body blocking a fraction of the gas disc causing the absorption, implying that the absorbing gas is between the white dwarf and the transiting objects. Our results also demonstrate the capability of EMCCDs to perform high-quality time resolved spectroscopy of relatively faint targets.

Roger E. Moore
2018-Oct-16, 01:20 PM
Back to disintegrating Jovian planets. I count this one as disintegrating, others might not, YMMV. Wonder if the "flare" was a superflare, or what.


Atmospheric dynamics and the variable transit of KELT-9 b

P. Wilson Cauley, et al. (Submitted on 13 Oct 2018)

We present a resolved detection of the optical Mg I triplet at 7.8σ in the extended atmosphere of the ultra-hot Jupiter KELT-9 b, adding to the list of detected metal species in the hottest gas giant currently known. Constraints are placed on the density and radial extent of the excited hydrogen envelope using simultaneous observations of Hα and Hβ under the assumption of a spherically symmetric atmosphere. We find that planetary rotational broadening of v rot =12.0 +0.7 −0.4 km s −1 is necessary to reproduce the Balmer line transmission profile shapes, although the in-transit profiles may be contaminated by non-rotational mass flow components. The time-series of both metal line and hydrogen absorption show remarkable structure, suggesting that the atmosphere observed during this transit is dynamic rather than static. We detect a relative emission feature near the end of the transit which shows a P-Cygni-like shape, evidence of material moving at ≈50−100 km s −1 away from the planet. We hypothesize that the in-transit variability and subsequent P-Cygni-like profiles are due to a flaring event that caused the atmosphere to expand, resulting in unbound material being accelerated to high speeds by stellar radiation pressure. Further spectroscopic transit observations will help establish the frequency of such events.

QUOTES: The hottest gas giant discovered so far is KELT-9 b (Gaudi et al. 2017), which orbits at a distance of 0.034 AU from its A0V/B9V host star (Teff = 10170450 K) with a dayside equilibrium temperature of Teq ~ 4600 K. Kitzmann et al. (2018) showed that KELT-9 b's high temperature, which should dissociate most refractory molecules into their constituent atoms, could produce a suite of observable Fe I and Fe II lines in the optical. This prediction was validated by Hoeijmakers et al. (2018) who detected a strong cross-correlation signal in optical Fe I, Fe II, and Ti II lines. Yan & Henning (2018), via absorption at H-alpha, detected the presence of an optically thick layer of excited hydrogen around KELT-9 b and estimated the planetary mass loss rate to be ~ 10^12 g s-1.

Here we present the first exoplanet atmosphere detection of the optical Mg I triplet around KELT-9 b using the PEPSI spectrograph (Strassmeier et al. 2015) on the Large Binocular Telescope (LBT; 2 x 8.4 m). Magnesium absorption can be used to estimate exoplanet mass loss rates (Bourrier et al. 2015) and is an important coolant in hot planet atmospheres (Huang et al. 2017). We also confirm the H-alpha measurement of Yan & Henning (2018) and provide additional constraints on the extended hydrogen atmosphere using simultaneous observations of H-beta. Atmospheric models of the Mg I and Balmer line absorption favor non-zero planetary rotation velocities. Finally, we observe significant in-transit variability in all of the planetary absorption lines and large blue-shifted velocities in the transmission profiles near the end of the transit. We hypothesize that a stellar flare event is responsible for the variability and an increase in the planet's mass loss rate, where the expanding material is accelerated to high velocities by stellar radiation pressure.

Roger E. Moore
2018-Oct-21, 11:47 PM
More on the worse-case scenario disintegrating gas giant, Kelt-9b.



Extremely Irradiated Hot Jupiters: Non-Oxide Inversions, H- Opacity, and Thermal Dissociation of Molecules

Joshua D. Lothringer, Travis Barman, Tommi Koskinen (Submitted on 30 Apr 2018)

Extremely irradiated hot Jupiters, exoplanets reaching dayside temperatures >2000 K, stretch our understanding of planetary atmospheres and the models we use to interpret observations. While these objects are planets in every other sense, their atmospheres reach temperatures at low pressures comparable only to stellar atmospheres. In order to understand our \textit{a priori} theoretical expectations for the nature of these objects, we self-consistently model a number of extreme hot Jupiter scenarios with the PHOENIX model atmosphere code. PHOENIX is well-tested on objects from cool brown dwarfs to expanding supernovae shells and its expansive opacity database from the UV to far-IR make PHOENIX well-suited for understanding extremely irradiated hot Jupiters. We find several fundamental differences between hot Jupiters at temperatures >2500 K and their cooler counterparts. First, absorption by atomic metals like Fe and Mg, molecules including SiO and metal hydrides, and continuous opacity sources like H− all combined with the short-wavelength output of early-type host stars result in strong thermal inversions, without the need for TiO or VO. Second, many molecular species, including H2O, TiO, and VO are thermally dissociated at pressures probed by eclipse observations, biasing retrieval algorithms that assume uniform vertical abundances. We discuss other interesting properties of these objects, as well as future prospects and predictions for observing and characterizing this unique class of astrophysical object, including the first self-consistent model of the hottest known jovian planet, KELT-9b.

QUOTES: Lower mass extreme hot Jupiters present an interesting test case for models of atmospheric escape. The high temperatures in their atmospheres, not limited to the thermosphere, dissociate molecules deeper than on moderate hot Jupiters, and can lead to rapid escape enhanced by Roche lobe overflow. KELT-9b, the hottest known Jovian exoplanet (Tdayside = 4,600 K), is particularly interesting. Gaudi et al. (2017) estimated a range of mass loss rates for this planet based on the energy-limited formalism. Their upper limit on the mass-loss rate implied that the planet would lose its entire atmosphere in only 600 Myr, similar to the main-sequence lifetime of its A0-type host star.

... Between 2 and 12 microns, the brightness temperature of KELT-9b increases by nearly 1,000 K. H− becomes important when hydrogen is in its atomic form and a supply of free electrons exist. For a planet like KELT-9b, atomic hydrogen is the most abundant species throughout the atmosphere until about a microbar when H+ and e− become the main constituents.



The Peculiar Atmospheric Chemistry of KELT-9b

Daniel Kitzmann, et al. (Submitted on 19 Apr 2018 (v1), last revised 12 Jul 2018 (this version, v3))

The atmospheric temperatures of the ultra-hot Jupiter KELT-9b straddle the transition between gas giants and stars, and therefore between two traditionally distinct regimes of atmospheric chemistry. Previous theoretical studies assume the atmosphere of KELT-9b to be in chemical equilibrium. Despite the high ultraviolet flux from KELT-9, we show using photochemical kinetics calculations that the observable atmosphere of KELT-9b is predicted to be close to chemical equilibrium, which greatly simplifies any theoretical interpretation of its spectra. It also makes the atmosphere of KELT-9b, which is expected to be cloudfree, a tightly constrained chemical system that lends itself to a clean set of theoretical predictions. Due to the lower pressures probed in transmission (compared to emission) spectroscopy, we predict the abundance of water to vary by several orders of magnitude across the atmospheric limb depending on temperature, which makes water a sensitive thermometer. Carbon monoxide is predicted to be the dominant molecule under a wide range of scenarios, rendering it a robust diagnostic of the metallicity when analyzed in tandem with water. All of the other usual suspects (acetylene, ammonia, carbon dioxide, hydrogen cyanide, methane) are predicted to be subdominant at solar metallicity, while atomic oxygen, iron and magnesium are predicted to have relative abundances as high as 1 part in 10,000. Neutral atomic iron is predicted to be seen through a forest of optical and near-infrared lines, which makes KELT-9b suitable for high-resolution ground-based spectroscopy with HARPS-N or CARMENES. We summarize future observational prospects of characterizing the atmosphere of KELT-9b.

QUOTES: In the current study, we have explored the atmospheric chemistry of ultra-hot Jupiters for which KELT-9b is an archetype. In contrast to other studies (Arcangelietal. 2018; Kreidberg et al. 2018; Lothringer et al. 2018; Mansfield et al.2018;Parmentieretal.2018),we do not assume chemical equilibrium in our calculations, but instead perform photochemical kinetics calculations, which explicitly quantify the effects of atmospheric mixing and photochemistry. We then further explore the atmospheric chemistry using chemical equilibrium calculations that include a set of metals. Our findings include: • Photochemistry, rather than atmospheric mixing, is the main driver for disequilibrium chemistry at low pressures. Nevertheless, at pressures probed by optical and infrared spectroscopy at low resolution, chemical equilibrium is a reasonable approximation. • When analyzed in tandem, the abundances of carbon monoxide and water allows one to completely solve for C/H, O/H and temperature, provided that chemical equilibrium is assumed. • Metals in their atomic form are predicted to be observable. In particular, atomic iron should be seen via a forest of optical and near-infrared lines using high-resolution ground-based spectrographs such as HARPS-N and CARMENES

Roger E. Moore
2018-Oct-22, 12:30 AM
A little wishful planning for the James Webb mission, which everyone hopes doesn't go into the Atlantic.


Inferring the Composition of Disintegrating Planet Interiors from Dust Tails with Future James Webb Space Telescope Observations

Eva H. L. Bodman, Jason T. Wright, Steven J. Desch, Carey M. Lisse (Submitted on 21 Aug 2018)

Disintegrating planets allow for the unique opportunity to study the composition of the interiors of small, hot, rocky exoplanets because the interior is evaporating and that material is condensing into dust, which is being blown away and then transiting the star. Their transit signal is dominated by dusty effluents forming a comet-like tail trailing the host planet (or leading it, in the case of K2-22b), making these good candidates for transmission spectroscopy. To assess the ability of such observations to diagnose the dust composition, we simulate the transmission spectra from 5-14 μm for the planet tail assuming an optically-thin dust cloud comprising a single dust species with a constant column density scaled to yield a chosen visible transit depth. We find that silicate resonant features near 10 μm can produce transit depths that are at least as large as those in the visible. For the average transit depth of 0.55% in the Kepler band for K2-22b, the features in the transmission spectra can be as large as 1%, which is detectable with the JWST MIRI low-resolution spectrograph in a single transit. The detectability of compositional features is easier with an average grain size of 1 μm despite features being more prominent with smaller grain sizes. We find most features are still detectable for transit depths of ~0.3% in the visible range. If more disintegrating planets are found with future missions such as the space telescope TESS, follow-up observations with JWST can explore the range of planetary compositions.

QUOTES: During the Kepler mission (Borucki et al. 2009), a new subset of the ultra-short period planets (“USP planets,” e.g. Sanchis-Ojeda et al. 2014), referred to as “disintegrating planets” was discovered. These appear to have large dusty tails as a result of their disintegration, presumably due to the intense irradiation of their host star (e.g. KIC 12557548, Rappaport et al. 2012). The transits of these disintegrating planets are characterized by a sharp and steep ingress followed by an extended tail-like egress or the reverse (extended ingress and steep egress) as in the case of K2-2b. Some systems also show a short brightening before the ingress and a brightening after the egress, suggestive of forward scattering in a dust tail. Currently, the most promising hypothesis for these systems is a low-mass (lunar or Mercury-like) disintegrating planet surrounded by escaping dusty effluents that form a comet-like tail much larger (∼10x) than the rocky planet itself (Rappaport et al. 2012). The dayside temperatures of these planets (∼2000K) are high enough to evaporate rock and cause large mass loss. The transit depths of these planets are highly variable, possibly due to changes in the dust production rate which may linked to stellar activity (Croll et al. 2015; Kawahara et al. 2013).

Roger E. Moore
2018-Oct-25, 01:12 AM
Nice to get some news again about "breaking up".


Back to "Normal" for the Disintegrating Planet Candidate KIC 12557548 b

Everett Schlawin, et al. (Submitted on 23 Oct 2018)

KIC 12557548 b is first of a growing class of intriguing disintegrating planet candidates, which lose mass in the form of a metal rich vapor that condenses into dust particles. Here, we follow up two perplexing observations of the system: 1) the transits appeared shallower than average in 2013 and 2014 and 2) the parameters derived from a high resolution spectrum of the star differed from other results using photometry and low resolution spectroscopy. We observe 5 transits of the system with the 61-inch Kuiper telescope in 2016 and show that they are consistent with photometry from the Kepler spacecraft in 2009-2013, suggesting that the dusty tail has returned to normal length and mass. We also evaluate high resolution archival spectra from the Subaru HDS spectrograph and find them to be consistent with a main-sequence Teff=4440 +/- 70 K star in agreement with the photometry and low resolution spectroscopy. This disfavors the hypothesis that planet disintegration affected the analysis of prior high resolution spectra of this star. We apply Principal Component Analysis to the Kepler long cadence data to understand the modes of disintegration. There is a tentative 491 day periodicity of the second principal component, which corresponds to possible long-term evolution of the dust grain sizes, though the mechanism on such long timescales remains unclear.

Roger E. Moore
2018-Nov-07, 02:28 PM
More news on what I think of as disintegrating Jovian planets.


Atmospheric mass loss from hot Jupiters irradiated by stellar superflares

D. V. Bisikalo, V.I. Shematovich, A.A. Cherenkov, L. Fossati, C. Moestl (Submitted on 6 Nov 2018)

Because of their activity, late-type stars are known to host powerful flares producing intense high-energy radiation on short time-scales that may significantly affect the atmosphere of nearby planets. We employ a one-dimensional aeronomic model to study the reaction of the upper atmosphere of the hot Jupiter HD 209458b to the additional high-energy irradiation caused by a stellar flare. Atmospheric absorption of the additional energy produced during a flare leads to local atmospheric heating, accompanied by the formation of two propagating shock waves. We present estimates of the additional atmospheric loss occurring in response to the flare. We find the mass loss rate at the exobase level to significantly increase (3.8*10^10, 8*10^10, and 3.5*10^11 g s-1 for 10, 100, and 1000 times the high-energy flux of the quiet star, respectively) in comparison to that found considering the inactive star (2*10^10 g s-1).

Roger E. Moore
2018-Nov-14, 02:44 AM
More on disintegrating super-Jupiters, especially KELT-9b.


XUV Radiation from A-stars: Implications for Ultra-hot Jupiters

L. Fossati, et al. (Submitted on 13 Nov 2018)

Extremely irradiated, close-in planets to early-type stars might be prone to strong atmospheric escape. We review the literature showing that X-ray-to-optical measurements indicate that for intermediate-mass stars (IMS) cooler than ≈8250 K, the X-ray and EUV (XUV) fluxes are on average significantly higher than those of solar-like stars, while for hotter IMS, because of the lack of surface convection, it is the opposite. We construct spectral energy distributions for prototypical IMS, comparing them to solar. The XUV fluxes relevant for upper planet atmospheric heating are highest for the cooler IMS and lowest for the hotter IMS, while the UV fluxes increase with increasing stellar temperature. We quantify the influence of this characteristic of the stellar fluxes on the mass loss of close-in planets by simulating the atmospheres of planets orbiting EUV-bright (WASP-33) and EUV-faint (KELT-9) A-type stars. For KELT-9b, we find that atmospheric expansion caused by heating due to absorption of the stellar UV ad optical light drives mass-loss rates of ≈10^11 g s−1, while heating caused by absorption of the stellar XUV radiation leads to mass-loss rates of ≈10^10 g s−1, thus underestimating mass loss. For WASP-33b, the high XUV stellar fluxes lead to mass-loss rates of ≈10^11 g s−1. Even higher mass-loss rates are possible for less massive planets orbiting EUV-bright IMS. We argue that it is the weak XUV stellar emission, combined with a relatively high planetary mass, which limit planetary mass-loss rates, to allow the prolonged existence of KELT-9-like systems.

Roger E. Moore
2018-Dec-06, 05:21 PM
Giant planet WASP-12b is going to crash into its star sooner than expected.


Obliquity Tides May Drive WASP-12b's Rapid Orbital Decay

Sarah Millholland, Gregory Laughlin (Submitted on 4 Dec 2018)

Recent analyses have revealed a mystery. The orbital period of the highly inflated hot Jupiter, WASP-12b, is decreasing rapidly. The rate of inspiral, however, is too fast to be explained by either eccentricity tides or equilibrium stellar tides. While dynamical stellar tides are possible, they require a subgiant structure for the star, whereas stellar models point toward a main sequence host. Here, we show that these hitherto irreconcilable observations might be explained by planetary obliquity tides if planet b's spin vector is trapped in a high-obliquity state maintained by a secular spin-orbit resonance with an unseen exterior perturbing planet. We derive constraints on the obliquity (ε≳50 ∘ ), reduced tidal quality factor (Q ′ ∼10 6 −10 7 ), and perturbing planet parameters (M 2 ∼10−20M ⊕ , a 2 ≲0.04AU ) required to generate the observed orbital decay. Direct N-body simulations that include tidal and spin dynamics reinforce the plausibility of the scenario. Furthermore, we show that the resonance could have been captured when planet b's obliquity was small, making the proposed sequence of events easy to explain. The hypothetical perturbing planet is within the limits of current radial velocity constraints on the system yet is also detectable. If it exists, it could provide evidence in favor of the in situ formation hypothesis for hot Jupiters.

Roger E. Moore
2018-Dec-07, 02:00 PM
Even more on WASP-12b. Trust me, I so want to watch this planet crash into its sun... on remote TV only, not live and in person, of course.


Planet-star interactions with precise transit timing. I. The refined orbital decay rate for WASP-12 b and initial constraints for HAT-P-23 b, KELT-1 b, KELT-16 b, WASP-33 b, and WASP-103 b

G. Maciejewski, et al. (Submitted on 6 Dec 2018)

Theoretical calculations and some indirect observations show that massive exoplanets on tight orbits must decay due to tidal dissipation within their host stars. This orbital evolution could be observationally accessible through precise transit timing over a course of decades. The rate of planetary in-spiralling may not only help us to understand some aspects of evolution of planetary systems, but also can be used as a probe of the stellar internal structure. In this paper we present results of transit timing campaigns organised for a carefully selected sample of hot Jupiter-like planets which were found to be the best candidates for detecting planet-star tidal interactions on the Northern hemisphere. Among them, there is the WASP-12 system which is the best candidate for possessing an in-falling giant exoplanet [[emphasis mine--REM]]. Our new observations support the scenario of orbital decay of WASP-12 b and allow us to refine its rate. The derived tidal quality parameter of the host star Q'_{*} = (1.82 +/- 0.32) x 10^5 is in agreement with theoretical predictions for subgiant stars. For the remaining systems - HAT-P-23, KELT-1, KELT-16, WASP-33, and WASP-103 - our transit timing data reveal no deviations from the constant-period models, hence constraints on the individual rates of orbital decay were placed. The tidal quality parameters of host stars in at least 4 systems - HAT-P-23, KELT-1, WASP-33, and WASP-103 - were found to be greater than the value reported for WASP-12. This is in line with the finding that those hosts are main sequence stars, for which efficiency of tidal dissipation is predicted to be relatively weak.

Roger E. Moore
2018-Dec-07, 04:44 PM
More on ultrahot gas giants losing their atmospheres.


An exoplanet loses its atmosphere in the form of a tail

December 6, 2018, Instituto de Astrofísica de Canarias

A new study led by scientists from the Instituto de Astrofísica de Canarias (IAC) reveals that the giant exoplanet WASP-69b carries a comet-like tail made up of helium particles escaping from its gravitational field and propelled by the ultraviolet radiation of its star. The results of this work are published today in the journal Science.

The planet was observed during a transit, when it passed in front of its host star. During this event, the planet and its atmosphere eclipse part of the starlight. "We observed a stronger and longer-lasting dimming of the starlight in a region of the spectrum where helium gas absorbs light," says Lisa Nortmann, a researcher at the IAC and lead author of the article published today in the journal Science. "The longer duration of this absorption allows us to infer the presence of a tail," she adds.

But this is not the only result described in the article. The authors have also analyzed four other planets in a similar way. These are the hot exoplanets HD 189733b and HD 209458b, which have a mass similar to that of Jupiter, the extremely hot giant planet KELT-9b and the warm Neptune-sized exoplanet GJ 436b. The analysis does not show extensive helium exospheres around the last three planets, which defies previous theoretical predictions. The hot Jupiter HD 189733b, on the other hand, does reveal a clear signal of absorbing helium, although here, the helium envelope is more compact and does not form a tail.

Roger E. Moore
2018-Dec-13, 07:30 PM
Our hot disintegrating friend KELT-9b is back in the news.


A ground-based NUV secondary eclipse observation of KELT-9b

Matthew J. Hooton, Christopher A. Watson, Ernst J. W. de Mooij, Neale P. Gibson, Daniel Kitzmann (Submitted on 6 Dec 2018)

KELT-9b is a recently discovered exoplanet with a 1.49 d orbit around a B9.5/A0-type star. The unparalleled levels of UV irradiation it receives from its host star put KELT-9b in its own unique class of ultra-hot Jupiters, with an equilibrium temperature > 4000 K. The high quantities of dissociated hydrogen and atomic metals present in the dayside atmosphere of KELT-9b bear more resemblance to a K-type star than a gas giant. We present a single observation of KELT-9b during its secondary eclipse, taken with the Wide Field Camera on the Isaac Newton Telescope (INT). This observation was taken in the U-band, a window particularly sensitive to Rayleigh scattering. We do not detect a secondary eclipse signal, but our 3σ upper limit of 181 ppm on the depth allows us to constrain the dayside temperature of KELT-9b at pressures of ~30 mbar to 4995 K (3σ ). Although we can place an observational constraint of A g < 0.14, our models suggest that the actual value is considerably lower than this due to H − opacity. This places KELT-9b squarely in the albedo regime populated by its cooler cousins, almost all of which reflect very small components of the light incident on their daysides. This work demonstrates the ability of ground-based 2m-class telescopes like the INT to perform secondary eclipse studies in the NUV, which have previously only been conducted from space-based facilities.


I would think deformation comes before disintegration.


Detectability of shape deformation in short-period exoplanets

B. Akinsanmi, S. C. C. Barros, N. C. Santos, A. C. M. Correia, P. F. L. Maxted, G. Boué, J. Laskar (Submitted on 11 Dec 2018)

Short-period planets suffer from extreme tidal forces from their parent stars causing them to deform and attain non-spherical shapes. The planet shapes, modeled here as triaxial ellipsoids, can have an impact on the observed transit light curves and the planetary parameters derived. We investigate the detectability of tidal deformation in short-period planets from their transit light curves and the instrumental precision needed. We show how the detection of deformation from the light curve allows us to obtain an observational estimate of the second fluid Love number which gives valuable insight about the planet's internal structure. We adopted a model to calculate the shape of a planet due to the external potentials acting on it and used this model to modify the ellc transit tool. Our model is parameterized by the Love number, hence for a given light curve we can derive the value of the Love number that best matches the observations. We simulated the known cases of WASP-103b and WASP-121b expected to be highly deformed. Our analyses showed that instrumental precision ≤ 50ppm/min is needed to reliably estimate the Love number and detect tidal deformation. This precision can be achieved for WASP-103b in ~40 transits using HST and in ~300 transits using the forthcoming CHEOPS. However, fewer transits will be required for short-period planets that may be found around bright stars in the TESS and PLATO survey missions. The unprecedented precisions expected from PLATO and JWST can permit the detection of deformation with a single transit. However, the effects of instrumental and astrophysical noise must be well-considered as they can increase the number of transits required to reach the 50 ppm/min detection limit. We also show that improper modeling of limb darkening can act to bury signals related to the planet's shape thereby leading us to infer sphericity for a deformed planet.

Roger E. Moore
2018-Dec-13, 08:03 PM
A fast-boiling Neptune-type planet that will disappear before long...


Hubble finds far-away planet vanishing at record speed
December 13, 2018, Johns Hopkins University

The speed and distance at which planets orbit their respective blazing stars can determine each planet's fate—whether the planet remains a longstanding part of its solar system or evaporates into the universe's dark graveyard more quickly. In their quest to learn more about far-away planets beyond our own solar system, astronomers discovered that a medium-sized planet roughly the size of Neptune, GJ 3470b, is evaporating at a rate 100 times faster than a previously discovered planet of similar size, GJ 436b.

The findings, published today in the journal of Astronomy & Astrophysics, advance astronomers' knowledge about how planets evolve. "This is the smoking gun that planets can lose a significant fraction of their entire mass. GJ 3470b is losing more of its mass than any other planet we seen so far; in only a few billion years from now, half of the planet may be gone," said David Sing, Bloomberg Distinguished Professor at Johns Hopkins and an author on the study.

Roger E. Moore
2018-Dec-14, 03:34 PM
More on same "evaporating" exoplanet.

Hubble PanCET: An extended upper atmosphere of neutral hydrogen around the warm Neptune GJ 3470 b

V.Bourrier, et al. (Submitted on 12 Dec 2018)

GJ 3470b is a warm Neptune transiting an M-dwarf star at the edge of the evaporation desert. It offers the possibility of investigating how low-mass, close-in exoplanets evolve under the irradiation from their host stars. We observed three transits of GJ 3470b in the Lyman-alpha line with the Hubble Space Telescope (HST) as part of the Panchromatic Comparative Exoplanet Treasury (PanCET) program. Absorption signatures are detected with similar properties in all three independent epochs, with absorption depths of 35+-7% in the blue wing of the line, and 23+-5% in the red wing. The repeatability of these signatures, their phasing with the planet transit, and the radial velocity of the absorbing gas allow us to conclude that there is an extended upper atmosphere of neutral hydrogen around GJ 3470 b. We determine from our observations the stellar radiation pressure and XUV irradiation from GJ 3470 and use them to perform numerical simulations of the upper atmosphere of GJ 3470b with the EVaporating Exoplanets (EVE) code. The unusual redshifted signature can be explained by the damping wings of dense layers of neutral hydrogen that extend beyond the Roche lobe and are elongated in the direction of the planet motion. This structure could correspond to a shocked layer of planetary material formed by the collision of the expanding thermosphere with the wind of the star. The blueshifted signature is well explained by neutral hydrogen atoms escaping at rates of about 1e10 g s-1 that are blown away from the star by its strong radiation pressure and are quickly photoionized, resulting in a smaller exosphere than that of the warm Neptune GJ 436b. The stronger escape from GJ 3470b, however, may have led to the loss of about 4-35% of its current mass over its 2 Gyr lifetime.

Roger E. Moore
2019-Jan-07, 04:40 PM
Two new articles on disintegrating/evaporating planets...


The Search for Disintegrating Planets Orbiting White Dwarfs

Difo Cheri, Gerlinder
American Astronomical Society, AAS Meeting #233, id.#153.03 (01/2019)

White dwarfs are the end state for low to medium mass stars like our sun and are essentially the exposed cores of such stars. Once a star exhausts its hydrogen and leaves the main sequence, mass loss occurs which can disturb the orbital path of objects within its gravitational influence. In some cases, the star's planets will fall into a much closer orbit and begin to disintegrate which can occur either though destructive gravitational forces or through the vaporization of rocky surface material. This material is then accreted onto the surface of the white dwarf where it can be analysed to gain a better understanding of the composition of the objects which were destroyed. Recently, transits of disrupted planetary material have been detected around the white dwarf WD 1145+017, giving researchers a new way to study this phenomenon. Here we present a search for new WD 1145+017-like transiting systems through optical observational data conducted by both ground and space-based surveys. Our search utilizes white dwarf databases which have identified thousands of white dwarfs. The NASA Exoplanet Archive was used for the retrieval of light curve data for targets which were observed by the SuperWasp, KELT, and K2 exoplanet surveys. The light curve data was then processed using a Fourier Transform which can reveal periodic dips in stellar flux. So far we have not detected any new WD 1145+017-like systems, but if we are successful in the future, observation of such events provide researchers with a better understanding of the way planets are disrupted around white dwarfs and the planets' exact inner compositions.



Probing the Escaping Exoplanet Atmospheres with the Helium 1083 nm Line

Oklopcic, Antonija
American Astronomical Society, AAS Meeting #233, id.#226.06 (01/2019)

Atmospheric escape or mass loss is an important process in the evolution of atmospheres of extrasolar planets. However, there are many aspects of atmospheric escape that remain poorly understood, in part due to a small number of direct observations, obtained mostly via transit spectroscopy in the difficult-to-observe hydrogen Lyman-alpha line. In recent theoretical work (Oklopcic & Hirata, 2018), we demonstrated that the absorption line of helium at 1083 nm can be used as a powerful new diagnostic of escaping atmospheres. This line is accessible for ground-based observations using high-resolution spectrographs, which can enable more detailed studies of extended atmospheres for a much larger number of exoplanets than realistically possible with UV spectroscopy. Shortly after the theoretical prediction, excess absorption in the helium line was observed in WASP-107b (Spake et al., 2018) and HAT-P-11b (Allart et al., in press; Mansfield et al., in prep.). I will present new, improved theoretical models of upper planetary atmospheres used to interpret the observed 1083 nm transit absorption signatures and place constraints on the physical properties of extended exoplanet atmospheres. Observations in the helium 1083 nm line opened a new wavelength window into escaping atmospheres; by comparing the data with theoretical models, we can improve our understanding of the physical processes that drive atmospheric mass loss and, consequently, affect planetary evolution and demographics of planetary systems.

Roger E. Moore
2019-Jan-16, 01:47 PM
A planet that did not disintegrate but did undergo atmospheric erosion, leaving it airless. No doubt the first thing that happens to planets that actually disintegrate.


EPIC 247418783b : A rocky super-Earth in a 2.2 day orbit

Molly R. Kosiarek, et al. (Submitted on 14 Jan 2019)

EPIC 247418783 is a solar-type star with a radius of R_star = 0.899 ± 0.034 R_sun and mass of M_star=0.934 ± 0.038 M_sun. From K2 C13 data, we found one super-Earth planet (R_p = 1.589+0.095-0.072 R_Earth) transiting this star on a short period orbit (P = 2.225177 +6.6e-5 -6.8e-5 days). We followed this system up with adaptive-optic imaging and spectroscopy to derive stellar parameters, search for stellar companions, and determine a planet mass. From our 75 radial velocity measurements using HIRES on Keck I and HARPS-N on Telescopio Nazionale Galileo, we constrained the mass of EPIC 247418783b to M_p = 6.49 ± 1.16 M_Earth. We found it necessary to model correlated stellar activity radial velocity signals with a Gaussian process in order to more accurately model the effect of stellar noise on our data; the addition of the Gaussian process also improved the precision of this mass measurement. With a bulk density of 8.84+2.50-2.03 g cm-3, the planet is consistent with an Earth-like rock/iron composition and no substantial gaseous envelope. Such an envelope, if it existed in the past, was likely eroded away by photo-evaporation during the first billion years of the star's lifetime.

Roger E. Moore
2019-Jan-22, 07:59 PM
New item elaborating briefly on K2-22b's situation.


The disintegrating exoplanet K2-22b
January 21, 2019, Harvard-Smithsonian Center for Astrophysics

Exoplanet surveys have yielded many surprises over the years, and the discovery of "disintegrating" exoplanets was one of them. These are planets that produce asymmetric shapes in the dips of the light curves seen as they transit across the faces of their stars. The asymmetry is hypothesized to be due to tails of dusty material from the planets' disintegration. At present, only three such planets known around main sequence stars, one being K2-22b. There are currently over 3800 confirmed exoplanets, suggesting either that such objects are intrinsically rare or that they have very short lifetimes, in which case it is lucky to catch any in the act of disintegration. These systems have been under intense study to better understand their formation and evolution and to constrain the properties of the grains in the dust tails.

CfA astronomers George Zhou, Karen Collins, Allyson Bieryla, and Dave Latham were members of a team that obtained forty-five ground-based observations of the K2-22 system in their study of the evolution of its transit. K2-22b is a Neptune-sized exoplanet that orbits its star in only about nine hours; it is unusual in that it appears to have not only a trailing dust tail but a leading trail as well. The team's observations of the dust tails included observing the transits at multiple wavelengths to try to use color to characterize the dust grain size or composition, but except in one transit event no differences were seen. The color information is, however, consistent with the previous model of dust grains as being small—comparable to or smaller than optical light wavelengths.

The astronomers also confirmed the variability of the transits, thought to be evidence of the continuing rapid evolution of the dust tails. The scientists point out that this variability appears in all three disintegrating planets, and the shape variability occurs on all the timescales observed, from transit to transit and over several years. They conclude that a continuous observing campaign would be a valuable tool in unraveling the mystery of these dusty trails.

Roger E. Moore
2019-Jan-29, 07:47 PM
Recent paper investigating the disintegration/ evaporation of superhot giant planets, also exploring what they look like as they boil away. Ionosphere idea as prelude to boiling is nifty, too.


Sparkling nights and very hot days on WASP-18b: the formation of clouds and the emergence of an ionosphere

Ch. Helling, P. Gourbin, P. Woitke, V. Parmentier (Submitted on 24 Jan 2019)

WASP-18b is an utra-hot Jupiter with a temperature difference of upto 2500K between day and night. Such giant planets begin to emerge as planetary laboratory for understanding cloud formation and gas chemistry in well-tested parameter regimes in order to better understand planetary mass loss and for linking observed element ratios to planet formation and evolution. We aim to understand where clouds form, their interaction with the gas phase chemistry through depletion and enrichment, the ionisation of the atmospheric gas and the possible emergence of an ionosphere on ultra-hot Jupiters. We utilize 1D profiles from a 3D atmosphere simulations for WASP-18b as input for kinetic cloud formation and gas-phase chemical equilibrium calculations. We solve our kinetic cloud formation model for these 1D profiles that sample the atmosphere of WASP-18b at 16 different locations along the equator and in the mid-latitudes and derive consistently the gas-phase composition. The dayside of WASP-18b emerges as completely cloud-free due to the very high atmospheric temperatures. In contrast, the nightside is covered in geometrically extended and chemically heterogeneous clouds with disperse particle size distributions. The atmospheric C/O increases to >0.7 and the enrichment of the atmospheric gas with cloud particles is ρ d /ρ gas >10 −3 . The clouds that form at the limbs appear located farther inside the atmosphere and they are the least extended. Not all day-night terminator regions form clouds. The gas-phase is dominated by H 2 , CO, SiO, H 2 O, H 2 S, CH 4 , SiS. In addition, the dayside has a substantial degree of ionisation due to ions like Na + , K + , Ca + , Fe + . Al + and Ti + are the most abundant of their element classes. We find that WASP-18b, as one example for ultra-hot Jupiters, develops an ionosphere on the dayside.

Roger E. Moore
2019-Jan-30, 12:50 PM
More on hot exo-Jupiters that undergo severe mass loss from stellar heating.


Swift UVOT near-UV transit observations of WASP-121 b

M. Salz, P. C. Schneider, L. Fossati, S. Czesla, K. France, J. H. M. M. Schmitt (Submitted on 29 Jan 2019)

Close-in gas planets are subject to continuous photoevaporation that can erode their volatile envelopes. Today, ongoing mass loss has been confirmed in a few individual systems via transit observations in the ultraviolet spectral range. We demonstrate that the Ultraviolet/Optical Telescope (UVOT) onboard the Neil Gehrels Swift Observatory enables photometry to a relative accuracy of about 0.5% and present the first near-UV (200-270 nm, NUV) transit observations of WASP-121 b, a hot Jupiter with one of the highest predicted mass-loss rates. The data cover the orbital phases 0.85 to 1.15 with three visits. We measure a broad-band NUV transit depth of 2.10±0.29 %. While still consistent with the optical value of 1.55%, the NUV data indicate excess absorption of 0.55% at a 1.9σ level. Such excess absorption is known from the WASP-12 system, and both of these hot Jupiters are expected to undergo mass loss at extremely high rates. With a CLOUDY simulation, we show that absorption lines of Fe II in a dense extended atmosphere can cause broad-band NUV absorption at the 0.5% level. Given the numerous lines of low-ionization metals, the NUV range is a promising tracer of photoevaporation in the hottest gas planets.

Roger E. Moore
2019-Feb-06, 01:30 PM
This news fits better here than anywhere else: Asteroid disruptions near the Sun, and the reason why we don't seem to have Vulcanoids (near-Sun asteroids where the hypothetical planet Vulcan was thought to be).


Debris of asteroid disruptions close to the Sun

Quanzhi Ye, Mikael Granvik (Submitted on 5 Feb 2019)

The under-abundance of asteroids on orbits with small perihelion distances suggests that thermally-driven disruption may be an important process in the removal of rocky bodies in the Solar System. Here we report our study of how the debris streams arise from possible thermally-driven disruptions in the near-Sun region. We calculate that a small body with a diameter \gtrsim0.5 km can produce a sufficient amount of material to allow the detection of the debris at the Earth as meteor showers, and that bodies at such sizes thermally disrupt every \sim2 kyrs. We also find that objects from the inner parts of the asteroid belt are more likely to become Sun-approacher than those from the outer parts. We simulate the formation and evolution of the debris streams produced from a set of synthetic disrupting asteroids drawn from Granvik et al. (2016)'s near-Earth object population model, and find that they evolve 10--70 times faster than streams produced at ordinary solar distances. We compare the simulation results to a catalog of known meteor showers on Sun-approaching orbits. We show that there is a clear overabundance of Sun-approaching meteor showers, which is best explained by a combining effect of comet contamination and an extended disintegration phase that lasts up to a few kyrs. We suggest that a few asteroid-like Sun-approaching objects that brighten significantly at their perihelion passages could, in fact, be disrupting asteroids. An extended period of thermal disruption may also explain the widespread detection of transiting debris in exoplanetary systems.

Roger E. Moore
2019-Feb-11, 09:13 PM
Relevant to the issue of disintegrating planets around white dwarfs--what happens to the planets earlier in their existence while the WDs are in red giant stage.


Speeding past planets? Asteroids radiatively propelled by giant branch Yarkovsky effects

Dimitri Veras, Arika Higuchi, Shigeru Ida (Submitted on 7 Feb 2019)

Understanding the fate of planetary systems through white dwarfs which accrete debris crucially relies on tracing the orbital and physical properties of exo-asteroids during the giant branch phase of stellar evolution. Giant branch luminosities exceed the Sun's by over three orders of magnitude, leading to significantly enhanced Yarkovsky and YORP effects on minor planets. Here, we place bounds on Yarkovsky-induced differential migration between asteroids and planets during giant branch mass loss by modelling one exo-Neptune with inner and outer exo-Kuiper belts. In our bounding models, the asteroids move too quickly past the planet to be diverted from their eventual fate, which can range from: (i) populating the outer regions of systems out to 10^4-10^5 au, (ii) being engulfed within the host star, or (iii) experiencing Yarkovsky-induced orbital inclination flipping without any Yarkovsky-induced semi-major axis drift. In these violent limiting cases, temporary resonant trapping of asteroids with radii of under about 10 km by the planet is insignificant, and capture within the planet's Hill sphere requires fine-tuned dissipation. The wide variety of outcomes presented here demonstrates the need to employ sophisticated structure and radiative exo-asteroid models in future studies. Determining where metal-polluting asteroids reside around a white dwarf depends on understanding extreme Yarkovsky physics.


A white dwarf is eating something and we aren't sure what it is.


A New Generation of Cool White Dwarf Atmosphere Models. III. WD J2356−209: Accretion of a Planetesimal with an Unusual Composition

S. Blouin, P. Dufour, N.F. Allard, S. Salim, R.M. Rich, L.V.E. Koopmans (Submitted on 8 Feb 2019)

WD J2356−209 is a cool metal-polluted white dwarf whose visible spectrum is dominated by a strong and broad sodium feature. Although discovered nearly two decades ago, no detailed and realistic analysis of this star had yet been realized. In the absence of atmosphere models taking into account the nonideal high-density effects arising at the photosphere of WD J2356−209, the origin of its unique spectrum had remained nebulous. We use the cool white dwarf atmosphere code presented in the first paper of this series to finally reveal the secrets of this peculiar object and details about the planetesimal that polluted its atmosphere. Thanks to the improved input physics of our models, we find a solution that is in excellent agreement with the photometric observations and the visible spectrum. Our solution reveals that the photosphere of WD J2356−209 has a number density ratio of log Na/Ca = 1.0 ± 0.2, which is the highest ever found in a white dwarf. Since we do not know how long ago the accretion episode stopped (if it has), we cannot precisely determine the composition nor the mass of the accreted planetesimal. Nevertheless, all scenarios considered indicate that its composition is incompatible with that of chondrite-like material and that its mass was at least 10^21 g.

Roger E. Moore
2019-Feb-15, 02:24 PM
Neutron stars could eat planets, too.


Investigation of the asteroid-neutron star collision model for the repeating fast radio bursts

Jeremy L. Smallwood, Rebecca G. Martin, Bing Zhang (Submitted on 14 Feb 2019)

The origin of fast radio bursts (FRBs) is still a mystery. One model proposed to interpret the only known repeating object, FRB 121102, is that the radio emission is generated from asteroids colliding with a highly magnetized neutron star (NS). With N-body simulations, we model a debris disc around a central star with an eccentric orbit intruding NS. As the NS approaches the first periastron passage, most of the comets are scattered away rather than being accreted by the NS. To match the observed FRB rate, the debris belt would have to be at least three orders of magnitude more dense than the Kuiper belt. We also consider the rate of collisions on to the central object but find that the density of the debris belt must be at least four orders of magnitude more dense than the Kuiper belt. These discrepancies in the density arise even if (1) one introduces a Kuiper-belt like comet belt rather than an asteroid belt and assume that comet impacts can also make FRBs; (2) the NS moves 2 orders of magnitude slower than their normal proper-motion velocity due to supernova kicks; and (3) the NS orbit is coplanar to the debris belt, which provides the highest rate of collisions.

Roger E. Moore
2019-Feb-20, 02:28 PM
Citizen scientists find a VERY ancient white dwarf with TWO disintegrated-planet dust bands around it, changing theories on how white dwarfs get their busted planets.


A 3 Gyr White Dwarf with Warm Dust Discovered via the Backyard Worlds: Planet 9 Citizen Science Project

John H. Debes, et al. (Submitted on 19 Feb 2019)

Infrared excesses due to dusty disks have been observed orbiting white dwarfs with effective temperatures between 7200 K and 25000 K, suggesting that the rate of tidal disruption of minor bodies massive enough to create a coherent disk declines sharply beyond 1~Gyr after white dwarf formation. We report the discovery that the candidate white dwarf LSPM J0207+3331, via the Backyard Worlds: Planet 9 citizen science project and Keck Observatory follow-up spectroscopy, is hydrogen-dominated with a luminous compact disk (L IR /L ⋆ =14%) and an effective temperature nearly 1000K cooler than any known white dwarf with an infrared excess. The discovery of this object places the latest time for large scale tidal disruption events to occur at ∼ 3 Gyr past the formation of the host white dwarf, making new demands of dynamical models for planetesimal perturbation and disruption around post main sequence planetary systems. Curiously, the mid-IR photometry of the disk cannot be fully explained by a geometrically thin, optically thick dust disk as seen for other dusty white dwarfs, but requires a second ring of dust near the white dwarf's Roche radius. In the process of confirming this discovery, we found that careful measurements of WISE source positions can reveal when infrared excesses for white dwarfs are co-moving with their hosts, helping distinguish them from confusion noise.

Easily readable news article on the discovery, with illustration and discussion.


The Zooniverse website.



Roger E. Moore
2019-Mar-04, 03:50 PM
Another planetary death-spiral, but 1 billion yrs from now.


KELT-23b: A Hot Jupiter Transiting a Near-Solar Twin Close to the TESS and JWST Continuous Viewing Zones

Daniel Johns, et al. (Submitted on 28 Feb 2019)

We announce the discovery of KELT-23b, a hot Jupiter transiting the relatively bright (V=10.3 ) star BD+66 911 (TYC 4187-996-1), and characterize the system using follow-up photometry and spectroscopy. A global fit to the system yields T eff =5900±49K , M ∗ =0.945 +0.060 −0.054 M ⊙ , R ∗ =0.995±0.015R ⊙ , L ∗ =1.082 +0.051 −0.048 L ⊙ , logg ∗ =4.418 +0.026 −0.025 (cgs), and [Fe/H]=−0.105±49 . KELT-23b is a hot Jupiter with mass M P =0.938 +0.045 −0.042 M J , radius R P =1.322±0.025R J , and density ρ P =0.504 +0.038 −0.035 g cm −3 . Intense insolation flux from the star has likely caused KELT-23b to become inflated. The time of inferior conjunction is T 0 =2458149.40776±0.00091 BJD TDB and the orbital period is P=2.255353 +0.000031 −0.000030 days. Due to strong tidal interactions, the planet is likely to spiral into its host within roughly a Gyr. This system has one of the highest positive ecliptic latitudes of all transiting planet hosts known to date, placing it near the Transiting Planet Survey Satellite and James Webb Space Telescope continuous viewing zones. Thus we expect it to be an excellent candidate for long-term monitoring and follow-up with these facilities.

Roger E. Moore
2019-Mar-18, 02:46 PM
A search for sodium around two "evaporating" exoplanets, in an attempt to learn their composition.


Monitoring of the D Doublet of Neutral Sodium during Transits of Two "Evaporating" Planets

Eric Gaidos, Teruyuki Hirano, Megan Ansdell (Submitted on 14 Mar 2019)

Spectroscopic transit detection of constituents in winds from "evaporating" planets on close-in transiting orbits could provide desperately needed information on the composition, formation, and orbital evolution of such objects. We obtained high-resolution optical spectra of the host stars during a single transit of Kepler-1520b and two transits of K2-22b to search for transient, Doppler-shifted absorption in the D lines of neutral sodium. Sodium should be released in the same silicate vapor wind that lofts the dust responsible for the periodic "dips" in the light curve. We do not detect any absorption lines with depths >30% at the predicted Doppler-shifted wavelengths during any of the transits. Detection sensitivity is limited by instrumental resolution that dilutes the saturated lines, and blurring of the lines by Doppler acceleration due to the short orbital period of the planet and long integration times for these faint stars. A model of neutral sodium production, escape, and ionization by UV radiation suggests that clouds of partially ionized sodium that are comparable in size to the host stars and optically thick in the D lines could accompany the planets. We consider the prospects for future detections brought about by the TESS all-sky survey of brighter stars and the advent of high-resolution spectrographs on Extremely Large Telescopes.

Roger E. Moore
2019-Apr-01, 05:56 PM
An asteroid spins faster, for some reason, and promptly flies apart.


Hubble Telescope Views Spun-Up Asteroid Coming Apart
By Donna Weaver / Ray Villard, Space Telescope Science Institute March 31, 2019

A small asteroid has been caught in the process of spinning so fast it’s throwing off material, according to new data from NASA’s Hubble Space Telescope and other observatories. Images from Hubble show two narrow, comet-like tails of dusty debris streaming from the asteroid (6478) Gault. Each tail represents an episode in which the asteroid gently shed its material — key evidence that Gault is beginning to come apart.


LATE: More on same, slightly earlier paper I missed. (YORP means rotational spin increase)


The Sporadic Activity of (6478) Gault: A YORP-driven event?

Jan T. Kleyna, Olivier R. Hainaut, Karen J. Meech, Henry H. Hsieh, Alan Fitzsimmons, Marco Micheli, Jacqueline V. Keane, Larry Denneau, John Tonry, Aren Heinze, Bhuwan C. Bhatt, Devendra K. Sahu, Detlef Koschny, Ken W. Smith, Harald Ebeling, Robert Weryk, Heather Flewelling, Richard J. Wainscoat

(Submitted on 28 Mar 2019)

On 2019 January 5 a streamer associated with the 4--10 km main-belt asteroid (6478)~Gault was detected by the ATLAS sky survey, a rare discovery of activity around a main-belt asteroid. Archival data from ATLAS and Pan-STARRS1 show the trail in early December 2018, but not between 2010 and January 2018. The feature has significantly changed over one month, perfectly matching predictions of pure dust dynamical evolution and changes in observing geometry for a short release of dust around 2018 October 28. Follow-up observations with HST show a second narrow trail corresponding to a brief release of dust on 2018 December 30. Both releases occurred with negligible velocity. We find the dust grains to be fairly large, with power-law size distributions in the 10 −5 −10 −3 ~m range and power-law indices of ∼−1.5 . Three runs of ground-based data find a signature of ∼2h rotation, close to the rotational limit, suggesting that the activity is the result of landslides or reconfigurations after YORP spin-up.

Roger E. Moore
2019-Apr-04, 06:41 PM
Is this world the shattered remains of a planet's metallic core?


Heavy metal planet fragment survives destruction from dead star
by University of Warwick, April 4, 2019

A fragment of a planet that has survived the death of its star has been discovered by University of Warwick astronomers in a disc of debris formed from destroyed planets, which the star ultimately consumes. The iron and nickel rich planetesimal survived a system-wide cataclysm that followed the death of its host star, SDSS J122859.93+104032.9. Believed to have once been part of a larger planet, its survival is all the more astonishing as it orbits closer to its star than previously thought possible, going around it once every two hours.

Also see:

Roger E. Moore
2019-Apr-05, 12:35 PM
More on the white-dwarf planetoid mentioned above.


A planetesimal orbiting within the debris disc around a white dwarf star

Christopher J. Manser, et al. (Submitted on 3 Apr 2019)

Many white dwarf stars show signs of having accreted smaller bodies, implying that they may host planetary systems. A small number of these systems contain gaseous debris discs, visible through emission lines. We report a stable 123.4min periodic variation in the strength and shape of the CaII emission line profiles originating from the debris disc around the white dwarf SDSSJ122859.93+104032.9. We interpret this short-period signal as the signature of a solid body held together by its internal strength.

Roger E. Moore
2019-Apr-09, 01:17 PM
How the planets of white dwarfs cause themselves to be torn apart by their stars (blaming the victims as always).


Orbital relaxation and excitation of planets tidally interacting with white dwarfs

Dimitri Veras, et al. (Submitted on 5 Apr 2019)

Observational evidence of white dwarf planetary systems is dominated by the remains of exo-asteroids through accreted metals, debris discs, and orbiting planetesimals. However, exo-planets in these systems play crucial roles as perturbing agents, and can themselves be perturbed close to the white dwarf Roche radius. Here, we illustrate a procedure for computing the tidal interaction between a white dwarf and a near-spherical solid planet. This method determines the planet's inward and/or outward drift, and whether the planet will reach the Roche radius and be destroyed. We avoid constant tidal lag formulations and instead employ the self-consistent secular Darwin-Kaula expansions from Boué & Efroimsky (2019), which feature an arbitrary frequency dependence on the quality functions. We adopt wide ranges of dynamic viscosities and spin rates for the planet in order to straddle many possible outcomes, and provide a foundation for the future study of individual systems with known or assumed rheologies. We find that: (i) massive Super-Earths are destroyed more readily than minor planets (such as the ones orbiting WD 1145+017 and SDSS J1228+1040), (ii) low-viscosity planets are destroyed more easily than high-viscosity planets, and (iii) the boundary between survival and destruction is likely to be fractal and chaotic.

Roger E. Moore
2019-Apr-12, 01:24 PM
Possible transit sighting of material blasted away from ultrahot giant planet WASP-12b. Super awesome if so.


First Light of Engineered Diffusers at the Nordic Optical Telescope Reveal Time Variability in the Optical Eclipse Depth of WASP-12b

C. von Essen, et al. (Submitted on 10 Apr 2019)

We present the characterization of two engineered diffusers mounted on the 2.5 meter Nordic Optical Telescope, located at Roque de Los Muchachos, Spain. To assess the reliability and the efficiency of the diffusers, we carried out several test observations of two photometric standard stars, along with observations of one primary transit observation of TrES-3b in the red (R-band), one of CoRoT-1b in the blue (B-band), and three secondary eclipses of WASP-12b in V-band. The achieved photometric precision is in all cases within the sub-millimagnitude level for exposures between 25 and 180 seconds. Along a detailed analysis of the functionality of the diffusers, we add a new transit depth measurement in the blue (B-band) to the already observed transmission spectrum of CoRoT-1b, disfavouring a Rayleigh slope. We also report variability of the eclipse depth of WASP-12b in the V-band. For the WASP-12b secondary eclipses, we observe a secondary-depth deviation of about 5-sigma, and a difference of 6-sigma and 2.5-sigma when compared to the values reported by other authors in similar wavelength range determined from Hubble Space Telescope data. We further speculate about the potential physical processes or causes responsible for this observed variability.

QUOTE: The WASP-12 system is known to contain material eroded and blown from the planetary atmosphere by the extreme stellar irradiation (Fossati et al. 2013). We can only speculate if potentially the variable eclipse depth is not caused by the planetary dayside atmosphere, but by an in-homogeneous flow of escaping material. This material might form temporary clumps near the planet, which scatter a fraction of the star light towards the observer. In this scenario, the deep secondary eclipse would rather be caused by an occultation of the escaping material than by the occultation of the planet.

Roger E. Moore
2019-Apr-16, 02:19 PM
Too fast a spin means an asteroid destroyed, and Gault is on its way out.


Episodically Active Asteroid 6478 Gault

David Jewitt, Yoonyoung Kim, Jane Luu, Jayadev Rajagopal, Ralf Kotulla, Susan Ridgway, Wilson Liu (Submitted on 15 Apr 2019)

We present imaging and spectroscopic observations of 6478 Gault, a 6 km diameter inner main-belt asteroid currently exhibiting strong, comet-like characteristics. Three distinct tails indicate that ultra-slow dust (ejection speed 0.15+/-0.05 m/s) was emitted from Gault in separate episodes beginning UT 2018 October 28+/-5 (Tail A), UT 2018 December 31+/-5 (Tail B), and UT 2019 February 10+/-7, with durations of 10 to 20 days. With a mean particle radius 100 micron, the estimated masses of the tails are M_A = 2e7 kg, M_B = 3e6 kg and M_C = 3e5 kg, respectively, and the mass loss rates from the nucleus are 10 to 20 kg/s for Tail A, 2 to 3 kg/s for Tail B and about 0.2 kg/s for Tail C. In its optical colors Gault is more similar to C-type asteroids than to S-types, even though the latter are numerically dominant in the inner asteroid belt. A spectroscopic upper limit to the production of gas is set at 1 kg/s. Discrete emission in three protracted episodes effectively rules out an impact origin for the observed activity. Sublimation driven activity is unlikely given the inner belt orbit and the absence of detectable gas. In any case, sublimation would not easily account for the observed multiple ejections. The closest similarity is between Gault and active asteroid 311P/(2013 P5), an object showing repeated but aperiodic ejections of dust over a 9 month period. While Gault is 10 times larger than 311P/(2013 P5), and the spin-up time to radiation torques is 100 times longer, its properties are likewise most consistent with episodic emission from a body rotating near breakup.

Roger E. Moore
2019-Apr-17, 01:06 PM
A bit dense, but possibly of interest as it covers ultrahot gas giants that spiral into their parent stars (because of tides) and are thus destroyed.


Orbital decay of short-period gas giants under evolving tides

Jaime A. Alvarado, Carolina García Carmona (Submitted on 16 Apr 2019)

The discovery of many giant planets in close-in orbits and the effect of planetary and stellar tides in their subsequent orbital decay have been extensively studied in the context of planetary formation and evolution theories. Planets orbiting close to their host stars undergo close encounters, atmospheric photoevaporation, orbital evolution, and tidal interactions. In many of these theoretical studies, it is assumed that the interior properties of gas giants remain static during orbital evolution. Here we present a model that allows for changes in the planetary radius as well as variations in the planetary and stellar dissipation parameters, caused by the planet's contraction and change of rotational rates from the strong tidal fields. In this semi-analytical model, giant planets experience a much slower tidal-induced circularization compared to models that do not consider these instantaneous changes. We predict that the eccentricity damping time-scale increases about an order of magnitude in the most extreme case for too inflated planets, large eccentricities, and when the planet's tidal properties are calculated according to its interior structural composition. This finding potentially has significant implications on interpreting the period-eccentricity distribution of known giant planets as it may naturally explain the large number of non-circularized, close period currently known. Additionally, this work may help to constrain some models of planetary interiors, and contribute to a better insight about how tides affect the orbital evolution of extrasolar systems.

Roger E. Moore
2019-Apr-22, 06:51 PM

A Planetary Death Census
by Spencer Wallace | Apr 22, 2019 | Daily Paper Summaries | 0 comments

About this paper:
Title: The unbiased frequency of planetary signatures around single and binary white dwarfs using Spitzer and Hubble
Authors: Thomas G. Wilson, Jay Farihi, Boris T. Gänsicke, Andrew Swan

A crude but quick way to find white dwarfs that are in the process of destroying their planets is by searching for debris near the star. Any planet or asteroid that gets too close to a white dwarf experiences a strong tidal force that tears it apart. An example of this is shown in Figure 1. As an asteroid (or planet) gets torn to tiny pieces, it emits excessive amounts of infrared light. Because the star (and its debris) appear as nothing more than a tiny point of light, we see the infrared color of the star increase.

The authors of today’s paper use the Spitzer Space Telescope to hunt for debris around 210 white dwarf stars. Out of these targets, 15 of these stars are seen to have a companion star, while the other 195 are alone. The presence of planetary debris is determined using two separate methods. First, the authors measure the excess flux of the stars at a wavelength of 3.6 and 4.5 microns. Second, the authors measure a color excess, which is the difference in brightness of the objects at 3.6 and 4.5 microns compared to a plain, non-debris polluted white dwarf.

Roger E. Moore
2019-Apr-24, 02:58 PM
More on asteroid Gault, which seems to have fallen apart unexpectedly.


New Active Asteroid (6478) Gault

Man-To Hui, Yoonyoung Kim, Xing Gao (Submitted on 22 Apr 2019)

Main-belt asteroid (6478) Gault was observed to show cometary features in early 2019. To investigate the cause, we conducted BVR observations at Xingming Observatory, China, from 2019 January to April. The two tails were formed around 2018 October 26--November 08, and 2018 December 29--2019 January 08, respectively, and consisted of dust grains of ≳ 20 μ m to 3 mm in radius ejected at a speed of 0.15 ± 0.05 m s−1 and following a broken power-law size distribution bending at grain radius ∼70 μ m (bulk density 1 g cm−3 assumed). The total mass of dust within a 10^4 km-radius aperture around Gault declined from ∼9 × 10^6 kg since 2019 January at a rate of 2.28 ± 0.07 kg s−1 , but temporarily surged around 2019 March 25, because Earth thence crossed the orbital plane of Gault, within which the ejected dust was mainly distributed. No statistically significant colour or short-term lightcurve variation was seen. Nonetheless we argue that Gault is currently subjected to rotational instability. Using the available astrometry, we did not detect any nongravitational acceleration in the orbital motion of Gault.

Roger E. Moore
2019-May-07, 12:24 PM
A planet so hot, vaporized metals fill its atmosphere. Our old disintegrating friend, KELT-9b.


A spectral survey of an ultra-hot Jupiter: Detection of metals in the transmission spectrum of KELT-9 b

H.J. Hoeijmakers, et al. (Submitted on 6 May 2019)

Context: KELT-9 b exemplifies a newly emerging class of short-period gaseous exoplanets that tend to orbit hot, early type stars - termed ultra-hot Jupiters. The severe stellar irradiation heats their atmospheres to temperatures of ∼4,000 K, similar to the photospheres of dwarf stars. Due to the absence of aerosols and complex molecular chemistry at such temperatures, these planets offer the potential of detailed chemical characterisation through transit and day-side spectroscopy. Studies of their chemical inventories may provide crucial constraints on their formation process and evolution history.
Aims: To search the optical transmission spectrum of KELT-9 b for absorption lines by metals using the cross-correlation technique.
Methods: We analyse 2 transits observed with the HARPS-N spectrograph. We use an isothermal equilibrium chemistry model to predict the transmission spectrum for each of the neutral and singly-ionized atoms with atomic numbers between 3 and 78. Of these, we identify the elements that are expected to have spectral lines in the visible wavelength range and use those as cross-correlation templates.
Results: We detect absorption of Na I, Cr II, Sc II and Y II, and confirm previous detections of Mg I, Fe I, Fe II and Ti II. In addition, we find evidence of Ca I, Cr I, Co I, and Sr II that will require further observations to verify. The detected absorption lines are significantly deeper than model predictions, suggesting that material is transported to higher altitudes where the density is enhanced compared to a hydrostatic profile. There appears to be no significant blue-shift of the absorption spectrum due to a net day-to-night side wind. In particular, the strong Fe II feature is shifted by 0.18±0.27 km~s −1 , consistent with zero. Using the orbital velocity of the planet we revise the steller and planetary masses and radii.

Roger E. Moore
2019-May-16, 04:40 PM
A better picture is emerging from new studies of that white dwarf with the disintegrating asteroid around it.


Shallow Ultraviolet Transits of WD 1145+017

Siyi Xu, et al. (Submitted on 24 Apr 2019)

WD 1145+017 is a unique white dwarf system that has a heavily polluted atmosphere, an infrared excess from a dust disk, numerous broad absorption lines from circumstellar gas, and changing transit features, likely from fragments of an actively disintegrating asteroid. Here, we present results from a large photometric and spectroscopic campaign with Hubble, Keck , VLT, Spitzer, and many other smaller telescopes from 2015 to 2018. Somewhat surprisingly, but consistent with previous observations in the u' band, the UV transit depths are always shallower than those in the optical. We develop a model that can quantitatively explain the observed "bluing" and the main findings are: I. the transiting objects, circumstellar gas, and white dwarf are all aligned along our line of sight; II. the transiting object is blocking a larger fraction of the circumstellar gas than of the white dwarf itself. Because most circumstellar lines are concentrated in the UV, the UV flux appears to be less blocked compared to the optical during a transit, leading to a shallower UV transit. This scenario is further supported by the strong anti-correlation between optical transit depth and circumstellar line strength. We have yet to detect any wavelength-dependent transits caused by the transiting material around WD 1145+017.

QOUTES: The original K2 light curves reveal at least six stable periods, all between 4.5-5.0 hours, near the white dwarf tidal radius. Follow-up photometric observations show that the system is actively evolving and the light curve changes on a daily basis (Gansicke et al. 2016; Rappaport et al. 2016, 2017; Gary et al. 2017). Likely, the transits are caused by dusty fragments1 coming off the disintegrating asteroid (Veras et al. 2017) and each piece is actively producing dust for a few weeks to many months.

An important conclusion of our model is the alignment between the transiting fragment and circumstellar gas { the system is edge-on. This is consistent with the picture that the gas is likely to come from the fragment and is eventually accreted onto the white dwarf.

Roger E. Moore
2019-Jun-13, 02:03 PM
WASP-12b, an ultra-hot super-Jupiter, really is boiling away, the fastest mass loss ever discovered around such a world.


Mass Loss from the Exoplanet WASP-12b Inferred from Spitzer Phase Curves

Taylor J. Bell, et al. (Submitted on 11 Jun 2019)

The exoplanet WASP-12b is the prototype for the emerging class of ultra-hot, Jupiter-mass exoplanets. Past models have predicted--and near ultra-violet observations have shown--that this planet is losing mass. We present an analysis of two sets of 3.6 μ m and 4.5 μ m Spitzer phase curve observations of the system which show clear evidence of infrared radiation from gas stripped from the planet, and the gas appears to be flowing directly toward or away from the host star. This accretion signature is only seen at 4.5 μm, not at 3.6 μm, which is indicative either of CO emission at the longer wavelength or blackbody emission from cool, ≲ 600 K gas. It is unclear why WASP-12b is the only ultra-hot Jupiter to exhibit this mass loss signature, but perhaps WASP-12b's orbit is decaying as some have claimed, while the orbits of other exoplanets may be more stable; alternatively, the high energy irradiation from WASP-12A may be stronger than the other host stars. We also find evidence for phase offset variability at the level of 6.4σ (46.2∘) at 3.6 μm.

2019-Jun-22, 07:50 PM
The aliens behind THE JUPITER THEFT would find easy ramscooping there--PROFAC style.

Roger E. Moore
2019-Jun-24, 01:08 AM
How much gas does a disintegrating planet give off, and what kind of gas it is?


Search for gas from the disintegrating rocky exoplanet K2-22b

A. R. Ridden-Harper, I. A. G. Snellen, C. U. Keller, P. Mollière (Submitted on 20 Jun 2019)

[Abridged] Aims. We searched for circumplanetary sodium and ionized calcium gas around the disintegrating rocky exoplanet K2-22 b to constrain its gas-loss and sublimation processes.
Methods. We observed four transits of K2-22 b with X-shooter on ESO's Very Large Telescope to obtain time-series of intermediate-resolution (R ∼11400) spectra. Our analysis focused on the two sodium D lines (588.995 nm and 589.592 nm) and the Ca+ triplet (849.802 nm, 854.209 nm and 866.214 nm). Planet-related absorption is searched for in the velocity rest frame of the planet, which changes from ±66 km s−1 during the transit.
Results. Since K2-22 b exhibits highly variable transit depths, we analyzed the individual nights and their average. By injecting signals we reached 5σ upper-limits on the individual nights that ranged from 11% - 13% and 1.7% - 2.0% for the tail's sodium and ionized calcium absorption, respectively. Night 1 was contaminated by its companion star so we considered weighted averages with and without Night 1 and quote conservative 5σ limits without Night 1 of 9% and 1.4%, respectively. Assuming their mass fractions to be similar to those in the Earth's crust, these limits correspond to scenarios in which 0.04% and 35% of the transiting dust is sublimated and observed as absorbing gas. However, this assumes the gas to be co-moving with the planet. We show that for the high irradiation environment of K2-22 b, sodium and ionized calcium could be quickly accelerated to 100s of km s−1 due to radiation pressure and entrainment by the stellar wind, making them much more difficult to detect. No evidence for such possibly broad and blue-shifted signals are seen in our data.
Conclusions. Future observations aimed at observing circumplanetary gas should take into account the possible broad and blue-shifted velocity field of atomic and ionized species.

Roger E. Moore
2019-Jul-02, 06:15 PM
More on a local active asteroid, P/2016 G1, that flew apart several years ago.


Roger E. Moore
2019-Jul-17, 10:56 PM
Disintegrating asteroid 6478 Gault: all the details


Physical Characterization of Active Asteroid (6478) Gault

Juan A. Sanchez, et al. (Submitted on 15 Jul 2019)

Main belt asteroid (6478) Gault has been dynamically linked with two overlapping asteroid families: Phocaea, dominated by S-type asteroids, and Tamara, dominated by low-albedo C-types. This object has recently become an interesting case for study, after images obtained in late 2018 revealed that it was active and displaying a comet-like tail. Previous authors have proposed that the most likely scenarios to explain the observed activity on Gault were rotational excitation or merger of near-contact binaries. Here we use new photometric and spectroscopic data of Gault to determine its physical and compositional properties. Lightcurves derived from the photometric data showed little variation over three nights of observations, which prevented us from determining the rotation period of the asteroid. Using WISE observations of Gault and the near-Earth Asteroid Thermal Model (NEATM) we determined that this asteroid has a diameter <6 km. NIR spectroscopic data obtained with the Infrared Telescope Facility (IRTF) showed a spectrum similar to that of S-complex asteroids, and a surface composition consistent with H chondrite meteorites. These results favor a compositional affinity between Gault and asteroid (25) Phocaea, and rules out a compositional link with the Tamara family. From the spectroscopic data we found no evidence of fresh material that could have been exposed during the outburst episodes.

Roger E. Moore
2019-Jul-26, 04:34 PM
Disintegrating asteroid 6478 Gault turns out to be a blue Q, a silicate type, once the dust comes off.


Roger E. Moore
2019-Aug-08, 10:39 PM
Our old buddy WASP-12b is coming apart just everywhere, starting with the atmosphere.


Modelling atmospheric escape and MgII near-ultraviolet absorption of the highly irradiated hot Jupiter WASP-12b
N. K. Dwivedi, et al. (Submitted on 7 Aug 2019)

We present two-dimensional multi-fluid numerical modelling of the upper atmosphere of the hot Jupiter WASP-12b. The model includes hydrogen chemistry, and self-consistently describes the expansion of the planetary upper atmosphere and mass loss due to intensive stellar irradiation, assuming a weakly magnetized planet. We simulate the planetary upper atmosphere and its interaction with the stellar wind (SW) with and without the inclusion of tidal force and consider different XUV irradiation conditions and SW parameters. With the inclusion of tidal force, even for a fast SW, the escaping planetary material forms two streams, propagating towards and away from the star. The atmospheric escape and related mass loss rate reaching the value of 10^12 gs^-1 appear to be mostly controlled by the stellar gravitational pull. We computed the column density and dynamics of MgII ions considering three different sets of SW parameters and XUV fluxes. The simulations enable to compute the absorption at the position of the Mg h line and to reproduce the times of ingress and egress. In case of a slow SW and without accounting for tidal force, the high orbital velocity leads to the formation of a shock approximately in the direction of the planetary orbital motion. In this case, mass loss is proportional to the stellar XUV flux. At the same time, ignoring of tidal effects for WASP-12b is a strong simplification, so the scenario with a shock, altogether is an unrealistic one.