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Thread: Disintegrating Planets - some recent news

  1. #31
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    More on ultrahot gas giants losing their atmospheres.


    https://phys.org/news/2018-12-exopla...here-tail.html

    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.

  2. #32
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    Our hot disintegrating friend KELT-9b is back in the news.

    https://arxiv.org/abs/1812.02773

    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.

    https://arxiv.org/abs/1812.04538

    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.

  3. #33
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    A fast-boiling Neptune-type planet that will disappear before long...

    https://phys.org/news/2018-12-hubble...ay-planet.html

    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.

  4. #34
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    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.

  5. #35
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    Two new articles on disintegrating/evaporating planets...


    http://cdsads.u-strasbg.fr/abs/2019AAS...23315303D

    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.

    ======

    http://cdsads.u-strasbg.fr/abs/2019AAS...23322606O

    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.

  6. #36
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    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.

    https://arxiv.org/abs/1901.04558

    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.

  7. #37
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    New item elaborating briefly on K2-22b's situation.

    https://phys.org/news/2019-01-disint...et-k2-22b.html

    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.

  8. #38
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    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.

    https://arxiv.org/abs/1901.08640

    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.

  9. #39
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    More on hot exo-Jupiters that undergo severe mass loss from stellar heating.


    https://arxiv.org/abs/1901.10223

    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.

  10. #40
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    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).


    https://arxiv.org/abs/1902.01758

    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.

  11. #41
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    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.

    https://arxiv.org/abs/1902.02795

    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.

    https://arxiv.org/abs/1902.03219

    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.

  12. #42
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    Neutron stars could eat planets, too.


    https://arxiv.org/abs/1902.05203

    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.

  13. #43
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    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.

    https://arxiv.org/abs/1902.07073

    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.

    http://www.sci-news.com/astronomy/ri...arf-06923.html


    The Zooniverse website.

    https://www.zooniverse.org/projects/...orlds-planet-9


    .
    Last edited by Roger E. Moore; 2019-Feb-20 at 05:52 PM. Reason: add yet more news

  14. #44
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    Another planetary death-spiral, but 1 billion yrs from now.

    https://arxiv.org/abs/1903.00031

    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.

  15. #45
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    A search for sodium around two "evaporating" exoplanets, in an attempt to learn their composition.

    https://arxiv.org/abs/1903.06217

    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.

  16. #46
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    An asteroid spins faster, for some reason, and promptly flies apart.

    https://scitechdaily.com/hubble-tele...-coming-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)

    https://arxiv.org/abs/1903.12142

    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.
    Last edited by Roger E. Moore; 2019-Apr-01 at 07:16 PM.

  17. #47
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    Is this world the shattered remains of a planet's metallic core?

    https://phys.org/news/2019-04-heavy-...-survives.html

    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:
    http://science.sciencemag.org/content/364/6435/66
    http://science.sciencemag.org/content/364/6435/25

  18. #48
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    More on the white-dwarf planetoid mentioned above.

    https://arxiv.org/abs/1904.02163

    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.

  19. #49
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    How the planets of white dwarfs cause themselves to be torn apart by their stars (blaming the victims as always).

    https://arxiv.org/abs/1904.03195

    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.

  20. #50
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    Possible transit sighting of material blasted away from ultrahot giant planet WASP-12b. Super awesome if so.

    https://arxiv.org/abs/1904.05362

    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.

  21. #51
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    Too fast a spin means an asteroid destroyed, and Gault is on its way out.

    https://arxiv.org/abs/1904.07100

    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.

  22. #52
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    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.

    https://arxiv.org/abs/1904.07596

    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.

  23. #53
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    https://astrobites.org/2019/04/22/pl...-death-census/

    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.

  24. #54
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    More on asteroid Gault, which seems to have fallen apart unexpectedly.

    https://arxiv.org/abs/1904.10095

    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.

  25. #55
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    A planet so hot, vaporized metals fill its atmosphere. Our old disintegrating friend, KELT-9b.

    https://arxiv.org/abs/1905.02096

    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.

  26. #56
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    A better picture is emerging from new studies of that white dwarf with the disintegrating asteroid around it.

    https://arxiv.org/abs/1904.10896

    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.

  27. #57
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    WASP-12b, an ultra-hot super-Jupiter, really is boiling away, the fastest mass loss ever discovered around such a world.

    https://arxiv.org/abs/1906.04742

    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.

  28. #58
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    The aliens behind THE JUPITER THEFT would find easy ramscooping there--PROFAC style.

  29. #59
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    How much gas does a disintegrating planet give off, and what kind of gas it is?

    https://arxiv.org/abs/1906.08795

    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.

  30. #60
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    More on a local active asteroid, P/2016 G1, that flew apart several years ago.

    https://arxiv.org/abs/1907.00751

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