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Thread: Epsilon Eridani - Jovian planet, wait no, wait yes, no, yes....

  1. #1
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    Smile Epsilon Eridani - Jovian planet, wait no, wait yes, no, yes....

    The last of the Big Three from earlier days of exoplanetary science and science fiction: epsilon Eridani. https://en.wikipedia.org/wiki/Epsilo...ani_in_fiction

    Hubble confirmed the existence of a Jovian planet there: http://hubblesite.org/news_release/news/2006-32

    But some papers say the planet is not confirmed. Wikipedia hedges on it, too. https://en.wikipedia.org/wiki/Epsilon_Eridani

    A second planet ("c") is suspected.

    It is interesting that the recent focus on ε Eridani has not been on confirming its Jovian planet but instead on examining its dust rings.

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    Another planet?


    http://adsabs.harvard.edu/abs/2018ApJ...857..133B

    RADIO EMISSION FROM THE EXOPLANETARY SYSTEM ε ERIDANI

    T. S. Bastian, J. Villadsen, A. Maps, G. Hallinan, A. J. Beasley
    04/2018

    As part of a wider search for radio emission from nearby systems known or suspected to contain extrasolar planets, ε Eridani was observed by the Jansky Very Large Array (VLA) in the 2-4 GHz and 4-8 GHz frequency bands. In addition, as part of a separate survey of thermal emission from solarlike stars, ε Eri was observed in the 8-12 GHz and the 12-18 GHz bands of the VLA. Quasi-steady continuum radio emission from ε Eri was detected in the three high-frequency bands at levels ranging from 67-83 mu Jy. No significant variability is seen in the quasi-steady emission. The emission in the 2-4 GHz emission, however, is shown to be the result of a circularly polarized (up to 50%) radio pulse or
    are of a few minutes duration that occurred at the beginning of the observation. We consider the astrometric position of the radio source in each frequency band relative to the expected position of the K2V star and the purported planet. The quasi-steady radio emission at frequencies >=8 GHz is consistent with a stellar origin. The quality of the 4-8 GHz astrometry provides no meaningful constraint on the origin of the emission. The location of the 2-4 GHz radio pulse is > 2:5sigma from the star yet, based on the ephemeris of Benedict et al. (2006), it is not consistent with the expected location of the planet either. If the radio pulse has a planetary origin, then either the planetary ephemeris is incorrect or the emission originates from another planet.

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    http://adsabs.harvard.edu/abs/2018IJAsB..17...70C

    Water maser emission from exoplanetary systems

    Cosmovici, C. B.; Pogrebenko, S.
    01/2018

    Since the first discovery of a Jupiter-mass planet in 1995 more than 2000 exo-planets have been found to exist around main sequence stars. The detection techniques are based on the radial velocity method (which involves the measurement of the star's wobbling induced by the gravitational field of the orbiting giant planets) or on transit photometry by using space telescopes (Kepler, Corot, Hubble and Spitzer) outside the absorbing Earth atmosphere. From the ground, as infrared observations are strongly limited by atmospheric absorption, radioastronomy offers almost the only possible way to search for water presence and abundance in the planetary atmospheres of terrestrial-type planets where life may evolve. Following the discovery in 1994 of the first water maser emission in the atmosphere of Jupiter induced by a cometary impact, our measurements have shown that the water maser line at 22 GHz (1.35 cm) can be used as a powerful diagnostic tool for water search outside the solar system, as comets are able to deliver considerable amounts of water to planets raising the fascinating possibility of extraterrestrial life evolution. Thus in 1999 we started the systematic search for water on 35 different targets up to 50 light years away from the Sun. Here we report the first detection of the water maser emission from the exoplanetary systems Epsilon Eridani, Lalande 21185 and Gliese 581. We have shown the peculiar feasibility of water detection and its importance in the search for exoplanetary systems especially for the Astrobiology programs, given the possibility of long period observations using powerful radiotelescopes equipped with adequate spectrometers.

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    http://adsabs.harvard.edu/abs/2017MNRAS.471L..96J

    The relation between stellar magnetic field geometry and chromospheric activity cycles - I. The highly variable field of ε Eridani at activity minimum

    Jeffers, S. V.; Boro Saikia, S.; Barnes, J. R.; Petit, P.; Marsden, S. C.; Jardine, M. M.; Vidotto, A. A.; BCool Collaboration
    10/2017

    The young and magnetically active K dwarf epsilo Eridani exhibits a chromospheric activity cycle of about 3 yr. Previous reconstructions of its large-scale magnetic field show strong variations at yearly epochs. To understand how epsilo Eridani's large-scale magnetic field geometry evolves over its activity cycle, we focus on high-cadence observations spanning 5 months at its activity minimum. Over this time-span, we reconstruct three maps of epsilo Eridani's large-scale magnetic field using the tomographic technique of Zeeman-Doppler imaging. The results show that at the minimum of its cycle, epsilo Eridani's large-scale field is more complex than the simple dipolar structure of the Sun and 61 Cyg A at minimum. Additionally, we observe a surprisingly rapid regeneration of a strong axisymmetric toroidal field as epsilo Eridani emerges from its S-index activity minimum. Our results show that all stars do not exhibit the same field geometry as the Sun, and this will be an important constraint for the dynamo models of active solar-type stars.

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    http://adsabs.harvard.edu/abs/2017hst..prop15217C

    Imaging the predicted asteroid belt analogue around Epsilon Eridani

    Cahoy, Kerri
    08/2017

    We propose to take advantage of the STIS coronagraphic mode and advances in speckle subtraction techniques to probe for scattered light from Epsilon Eridani's predicted asteroid belt analog. This proposal tests for the presence of visible scattered light from a warm dust ring at 1 arcsecond with a 5e-5/as^2 contrast, predicted from observations of the 24 micron excess. Dust morphology and scattered light brightness (exozodi) present a significant challenge to future exoplanet imaging missions, and Epsilon Eridani is an excellent sunlike candidate for future exoplanet direct imaging missions due its easily accessible habitable zone. Either a detection of scattered light from this circumstellar dust population or a non-detection will place valuable constraints on the dust composition, morphology, and transport mechanisms at work in the system and inform future direct imaging efforts of this nearby star system.
    There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
    — Mark Twain, Life on the Mississippi (1883)

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    The Northern Arc of ε Eridani's Debris Ring as Seen by ALMA

    Mark Booth, William R. F. Dent, Andres Jordan, Jean-Francois Lestrade, Antonio S. Hales, Mark C. Wyatt, Simon Casassus, Steve Ertel, Jane S. Greaves, Grant M. Kennedy, Luca Matra, Jean-Charles Augereau and Eric Villard
    08/2017

    We present the first ALMA observations of the closest known extrasolar debris disc. This disc orbits the star ε Eri, a K-type star just 3.2 pc away. Due to the proximity of the star, the entire disc cannot fit within the ALMA field of view. Therefore, the observations have been centred 1800 North of the star, providing us with a clear detection of the northern arc of the ring, at a wavelength of 1.3 mm. The observed disc emission is found to be narrow with a width of just 11-13 AU. The fractional disc width we find is comparable to that of the Solar System's Kuiper Belt and makes this one of the narrowest debris discs known. If the inner and outer edges are due to resonances with a planet then this planet likely has a semi-major axis of 48 AU. We find tentative evidence for clumps in the ring, although there is a strong chance that at least one is a background galaxy. We confirm, at much higher significance, the previous detection of an unresolved emission at the star that is above the level of the photosphere and attribute this excess to stellar chromospheric emission.

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    http://adsabs.harvard.edu/abs/2017MNRAS.466.3973M

    Collisional parameters of planetesimal belts, precursor of debris disks, perturbed by a nearby giant planet

    F. Marzari and A. Dell’Oro
    04/2017

    Planetesimal belts are invoked to explain the prolonged existence of debris disks. Important parameters to model their collisional evolution and to compute the dust production rate are the intrinsic probability of collision Pi and the mean impact velocity Uc. If a planet orbits close to the belt, the values of both these parameters are affected by its secular perturbations yielding a strong correlation between eccentricity e and pericentre longitude w. We adopt a new algorithm to compute both Pi and Uc in presence of various levels of secular correlation due to different ratios between proper and forced eccentricity. We tested this algorithm in a standard case with a Jupiter–sized planet orbiting inside a putative planetesimal belt finding that it is less collisionally active compared to a self–stirred belt because of the e−̟w coupling. The eccentricity of the planet is an important parameter in determining the amount of dust production since the erosion rate is 10 times faster when the planet eccentricity increases from 0.1 to 0.6. Also the initial conditions of the belt (either warm or cold) and its average inclination strongly affects Pi and Uc and then its long term collisional evolution in presence of the planet. We finally apply our method to the planetesimal belts supposedly refilling the dust disks around HD 38529 and ε Eridani. In the most collisionally active configurations, only a small fraction of bodies smaller than 100 km are expected to be fragmented over a time–span of 4 Gyr.

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    http://adsabs.harvard.edu/abs/2017AJ....153..226S

    The Inner 25 au Debris Distribution in the ε Eri System

    Su, Kate Y. L.; De Buizer, James M.; Rieke, George H.; Krivov, Alexander V.; Löhne, Torsten; Marengo, Massimo; Stapelfeldt, Karl R.; Ballering, Nicholas P.; Vacca, William D.
    05/2017

    Debris disk morphology is wavelength dependent due to the wide range of particle sizes and size-dependent dynamics influenced by various forces. Resolved images of nearby debris disks reveal complex disk structures that are difficult to distinguish from their spectral energy distributions. Therefore, multi-wavelength resolved images of nearby debris systems provide an essential foundation to understand the intricate interplay between collisional, gravitational, and radiative forces that govern debris disk structures. We present the Stratospheric Observatory for Infrared Astronomy (SOFIA) 35 mum resolved disk image of ε Eri, the closest debris disk around a star similar to the early Sun. Combining with the Spitzer resolved image at 24 mum and 15-38 mum excess spectrum, we examine two proposed origins of the inner debris in ε Eri: (1) in situ planetesimal belt(s) and (2) dragged-in grains from the cold outer belt. We find that the presence of in situ dust-producing planetesmial belt(s) is the most likely source of the excess emission in the inner 25 au region. Although a small amount of dragged-in grains from the cold belt could contribute to the excess emission in the inner region, the resolution of the SOFIA data is high enough to rule out the possibility that the entire inner warm excess results from dragged-in grains, but not enough to distinguish one broad inner disk from two narrow belts.

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    http://adsabs.harvard.edu/abs/2017PhDT.......310M

    Millimeter Studies of Nearby Debris Disks

    MacGregor, Meredith Ann
    03/2017

    At least 20% of nearby main sequence stars are known to be surrounded by disks of dusty material resulting from the collisional erosion of planetesimals, similar to asteroids and comets in our own Solar System. The material in these `debris disks' is directly linked to the larger bodies, like planets, in the system through collisions and gravitational perturbations. Observations at millimeter wavelengths are especially critical to our understanding of these systems, since the large grains that dominate emission at these long wavelengths reliably trace the underlying planetesimal distribution. In this thesis, I have used state-of-the-art observations at millimeter wavelengths to address three related questions concerning debris disks and planetary system evolution: 1) How are wide-separation, substellar companions formed? 2) What is the physical nature of the collisional process in debris disks? And, 3) Can the structure and morphology of debris disks provide probes of planet formation and subsequent dynamical evolution? Using ALMA observations of GQ Lup, a pre-main sequence system with a wide-separation, substellar companion, I have placed constraints on the mass of a circumplanetary disk around the companion, informing formation scenarios for this and other similar systems (Chapter 2). I obtained observations of a sample of fifteen debris disks with both the VLA and ATCA at centimeter wavelengths, and robustly determined the millimeter spectral index of each disk and thus the slope of the grain size distribution, providing the first observational test of collision models of debris disks (Chapter 3). By applying an MCMC modeling framework to resolved millimeter observations with ALMA and SMA, I have placed the first constraints on the position, width, surface density gradient, and any asymmetric structure of the AU Mic, HD 15115, Epsilon Eridani, Tau Ceti, and Fomalhaut debris disks (Chapters 4--8). These observations of individual systems hint at trends in disk structure and dynamics, which can be explored further with a comparative study of a sample of the eight brightest debris disks around Sun-like stars within 20 pc (Chapter 9). This body of work has yielded the first resolved images of notable debris disks at millimeter wavelengths, and complements other ground- and space-based observations by providing constraints on these systems with uniquely high angular resolution and wavelength coverage. Together these results provide a foundation to investigate the dynamical evolution of planetary systems through multi-wavelength observations of debris disks.

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    http://adsabs.harvard.edu/abs/2017ApJ...836...49A

    Pale Orange Dots: The Impact of Organic Haze on the Habitability and Detectability of Earthlike Exoplanets

    Arney, Giada N.; Meadows, Victoria S.; Domagal-Goldman, Shawn D.; Deming, Drake; Robinson, Tyler D.; Tovar, Guadalupe; Wolf, Eric T.; Schwieterman, Edward
    02/2017

    Hazes are common in known planetary atmospheres, and geochemical evidence suggests that early Earth occasionally supported an organic haze with significant environmental and spectral consequences. The UV spectrum of the parent star drives organic haze formation through methane photochemistry. We use a 1D photochemical-climate model to examine production of fractal organic haze on Archean Earth-analogs in the habitable zones of several stellar types: the modern and early Sun, AD Leo (M3.5V), GJ 876 (M4V), ε Eridani (K2V), and sigma Boötis (F2V). For Archean-like atmospheres, planets orbiting stars with the highest UV fluxes do not form haze because of the formation of photochemical oxygen radicals that destroy haze precursors. Organic hazes impact planetary habitability via UV shielding and surface cooling, but this cooling is minimized around M dwarfs, whose energy is emitted at wavelengths where organic hazes are relatively transparent. We generate spectra to test the detectability of haze. For 10 transits of a planet orbiting GJ 876 observed by the James Webb Space Telescope, haze makes gaseous absorption features at wavelengths < 2.5 mum 2-10sigma shallower than a haze-free planet, and methane and carbon dioxide are detectable at >5sigma. A haze absorption feature can be detected at 5sigma near 6.3 mum, but a higher signal-to-noise ratio is needed to distinguish haze from adjacent absorbers. For direct imaging of a planet at 10 pc using a coronagraphic 10 m class ultraviolet-visible-near-infrared telescope, a UV-blue haze absorption feature would be strongly detectable at >12sigma in 200 hr.
    There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
    — Mark Twain, Life on the Mississippi (1883)

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    http://adsabs.harvard.edu/abs/2014ApJ...791L..11G

    Extreme Conditions in a Close Analog to the Young Solar System: Herschel Observations of epsilon Eridani

    Greaves, J. S.; Sibthorpe, B.; Acke, B.; Pantin, E. E.; Vandenbussche, B.; Olofsson, G.; Dominik, C.; Barlow, M. J.; Bendo, G. J.; Blommaert, J. A. D. L.; Brandeker, A.; de Vries, B. L.; Dent, W. R. F.; Di Francesco, J.; Fridlund, M.; Gear, W. K.; Harvey, P. M.; Hogerheijde, M. R.; Holland, W. S.; Ivison, R. J.; Liseau, R.; Matthews, B. C.; Pilbratt, G. L.; Walker, H. J.; Waelkens, C.
    08/2014

    Far-infrared Herschel images of the epsilon Eridani system, seen at a fifth of the Sun's present age, resolve two belts of debris emission. Fits to the 160 mum PACS image yield radial spans for these belts of 12-16 and 54-68 AU. The south end of the outer belt is ≈10% brighter than the north end in the PACS+SPIRE images at 160, 250, and 350 mum, indicating a pericenter glow attributable to a planet "c." From this asymmetry and an upper bound on the offset of the belt center, this second planet should be mildly eccentric (ec ≈ 0.03-0.3). Compared to the asteroid and Kuiper Belts of the young Sun, the epsilon Eri belts are intermediate in brightness and more similar to each other, with up to 20 km sized collisional fragments in the inner belt totaling ≈5% of an Earth mass. This reservoir may feed the hot dust close to the star and could send many impactors through the Habitable Zone, especially if it is being perturbed by the suspected planet epsilon Eri b, at semi-major axis ≈3 AU.

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    https://arxiv.org/abs/1211.7263

    The planet search programme at the ESO CES and HARPS. IV. The search for Jupiter analogues around solar-like stars

    M. Zechmeister (1,2), M. Kürster (2), M. Endl (3), G. Lo Curto (4), H. Hartman (5,6), H. Nilsson (6), T. Henning (2), A. P. Hatzes (7), W. D. Cochran (3) ((1) Institut für Astrophysik, Göttingen, (2) MPIA, Heidelberg, (3) University of Texas, Austin, (4) ESO, Garching, (5) Malmö University, (6) Lund Observatory, (7) TLS, Tautenburg)
    Submitted on 30 Nov 2012

    In 1992 we began a precision radial velocity (RV) survey for planets around solar-like stars with the Coude Echelle Spectrograph and the Long Camera (CES LC) at the 1.4 m telescope in La Silla (Chile). We have continued the survey with the upgraded CES Very Long Camera (VLC) and HARPS, both at the 3.6 m telescope, until 2007. The observations for 31 stars cover a time span of up to 15 years and the RV precision permit a search for Jupiter analogues. We perform a joint analysis for variability, trends, periodicities, and Keplerian orbits and compute detection limits. Moreover, the HARPS RVs are analysed for correlations with activity indicators (CaII H&K and CCF shape). We achieve a long-term RV precision of 15 m/s (CES+LC, 1992-1998), 9 m/s (CES+VLC, 1999-2006), and 2.8 m/s (HARPS, 2003-2009, including archive data), resp. This enables us to confirm the known planets around Iota Hor, HR 506, and HR 3259. A steady RV trend for Eps Ind A can be explained by a planetary companion. On the other hand, we find previously reported trends to be smaller for Beta Hyi and not present for Alp Men. The candidate planet Eps Eri b was not detected despite our better precision. [Emphasis mine--REM] Also the planet announced for HR 4523 cannot be confirmed. Long-term trends in several of our stars are compatible with known stellar companions. We provide a spectroscopic orbital solution for the binary HR 2400 and refined solutions for the planets around HR 506 and Iota Hor. For some other stars the variations could be attributed to stellar activity. The occurrence of two Jupiter-mass planets in our sample is in line with the estimate of 10% for the frequency of giant planets with periods smaller than 10 yr around solar-like stars. We have not detected a Jupiter analogue, while the detections limits for circular orbits indicate at 5 AU a sensitivity for minimum mass of at least 1 M_Jup (2 M_Jup) for 13% (61%) of the stars.

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    http://adsabs.harvard.edu/abs/2011A%26A...527A.140R

    Mass constraints on substellar companion candidates from the re-reduced Hipparcos intermediate astrometric data: nine confirmed planets and two confirmed brown dwarfs

    Reffert, S.; Quirrenbach, A.
    03/2011

    Context. The recently completed re-reduction of the Hipparcos data by van Leeuwen (2007a, Astrophysics and Space Science Library, 350) makes it possible to search for the astrometric signatures of planets and brown dwarfs known from radial velocity surveys in the improved Hipparcos intermediate astrometric data.
    Aims: Our aim is to put more significant constraints on the orbital parameters which cannot be derived from radial velocities alone, i.e. the inclination and the longitude of the ascending node, than was possible before. The determination of the inclination in particular allows to calculate an unambiguous companion mass, rather than the lower mass limit which can be obtained from radial velocity measurements.
    Methods: We fitted the astrometric orbits of 310 substellar companions around 258 stars, which were all discovered via the radial velocity method, to the Hipparcos intermediate astrometric data provided by van Leeuwen.
    Results: Even though the astrometric signatures of the companions cannot be detected in most cases, the Hipparcos data still provide lower limits on the inclination for all but 67 of the investigated companions, which translates into upper limits on the masses of the unseen companions. For nine companions the derived upper mass limit lies in the planetary and for 75 companions in the brown dwarf mass regime, proving the substellar nature of those objects. Two of those objects have minimum masses also in the brown dwarf regime and are thus proven to be brown dwarfs. The confirmed planets are the ones around Pollux (beta Gem b), ε Eri b, ε Ret b, mu Ara b, upsilo And c and d, 47 UMa b, HD 10647 b and HD 147513 b. The confirmed brown dwarfs are HD 137510 b and HD 168443 c. In 20 cases, the astrometric signature of the substellar companion was detected in the Hipparcos data, resulting in reasonable constraints on inclination and ascending node. Of these 20 companions, three are confirmed as planets or lightweight brown dwarfs (HD 87833 b, iota Dra b, and gamma Cep b), two as brown dwarfs (HD 106252 b and HD 168443 b), and four are low-mass stars (BD -04 782 b, HD 112758 b, rho CrB b, and HD169822 b). Of the others, many are either brown dwarfs or very low mass stars. For ε Eri, we derive a solution which is very similar to the one obtained using Hubble Space Telescope data.

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    http://adsabs.harvard.edu/abs/2006AJ....132.2206B

    The Extrasolar Planet ε Eridani b: Orbit and Mass

    Benedict, G. Fritz; McArthur, Barbara E.; Gatewood, George; Nelan, Edmund; Cochran, William D.; Hatzes, Artie; Endl, Michael; Wittenmyer, Robert; Baliunas, Sallie L.; Walker, Gordon A. H.; Yang, Stephenson; Kürster, Martin; Els, Sebastian; Paulson, Diane B.
    11/2006

    Hubble Space Telescope (HST) observations of the nearby (3.22 pc) K2 V star ε Eridani have been combined with ground-based astrometric and radial velocity data to determine the mass of its known companion. We model the astrometric and radial velocity measurements simultaneously to obtain the parallax, proper motion, perturbation period, perturbation inclination, and perturbation size. Because of the long period of the companion, ε Eri b, we extend our astrometric coverage to a total of 14.94 yr (including the 3 yr span of the HST data) by including lower precision ground-based astrometry from the Allegheny Multichannel Astrometric Photometer. Radial velocities now span 1980.8-2006.3. We obtain a perturbation period, P=6.85+/-0.03 yr, semimajor axis alpha=1.88+/-0.20 mas, and inclination i=30.1d+/-3.8d. This inclination is consistent with a previously measured dust disk inclination, suggesting coplanarity. Assuming a primary mass M*=0.83 M solar, we obtain a companion mass M=1.55MJ+/-0.24MJ. Given the relatively young age of ε Eri (~800 Myr), this accurate exoplanet mass and orbit can usefully inform future direct-imaging attempts. We predict the next periastron at 2007.3 with a total separation rho=0.3" at position angle P.A.=-27deg. Orbit orientation and geometry dictate that ε Eri b will appear brightest in reflected light very nearly at periastron. Radial velocities spanning over 25 yr indicate an acceleration consistent with a Jupiter-mass object with a period in excess of 50 yr, possibly responsible for one feature of the dust morphology, the inner cavity.
    There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
    — Mark Twain, Life on the Mississippi (1883)

  4. #4
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    The nearest Jovian planet to us, epsilon Eridani b, and very likely more planets. A young system, 200-800 million years old, which is as far back in the Precambrian as you can get.


    https://arxiv.org/abs/1810.03794

    Deep exploration of ε Eridani with Keck Ms-band vortex coronagraphy and radial velocities: mass and orbital parameters of the giant exoplanet
    Dimitri Mawet, et al. (Submitted on 9 Oct 2018)

    We present the most sensitive direct imaging and radial velocity (RV) exploration of ϵ Eridani to date. ϵ Eridani is an adolescent planetary system, reminiscent of the early Solar system. It is surrounded by a prominent and complex debris disk which is likely stirred by one or several gas giant exoplanets. The discovery of the RV signature of a giant exoplanet was announced 15 years ago, but has met with scrutiny due to possible confusion with stellar noise. We confirm the planet with a new compilation and analysis of precise RV data spanning 30 years, and combine it with upper limits from our direct imaging search, the most sensitive ever performed. The deep images were taken in the Ms band (4.7 μm) with the vortex coronagraph recently installed in W.M. Keck Observatory's infrared camera NIRC2, which opens a sensitive window for planet searches around nearby adolescent systems. The RV data and direct imaging upper limit maps were combined in an innovative joint Bayesian analysis, providing new constraints on the mass and orbital parameters of the elusive planet. ϵ Eridani b has a mass of 0.78 +0.38/−0.12 M-Jup and is orbiting ϵ Eridani at about 3.48 ± 0.02 AU with a period of 7.37 ± 0.07 years. The eccentricity of ϵ Eridani b's orbit is 0.07 +0.06/−0.05, an order of magnitude smaller than early estimates and consistent with a circular orbit. We discuss our findings from the standpoint of planet-disk interactions and prospects for future detection and characterization with the James Webb Space Telescope.
    There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
    — Mark Twain, Life on the Mississippi (1883)

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    Thumbs down

    Side Note: Separate threads were started for news about epsilon Eridani, tau Ceti, and epsilon Indi, as these have long been the "classic three" single sunlike stars that space enthusiasts and science-fiction writers hoped bore terrestrial planets, back since the days of Project Ozma.

    On epsilon Eridani in particular, the extremely young age of the system probably means we're not going to find a habitable planet there. I would guess that whatever planets are there are in Earth's Hadean period, and we'll need another billion years to even think about landing there.

    https://en.wikipedia.org/wiki/Hadean
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    There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
    — Mark Twain, Life on the Mississippi (1883)

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    This one is curious. Will look at it some more.


    https://arxiv.org/abs/1810.04194

    Possible detection of gamma rays from Epsilon Eridani

    Alexander H. Riley, et al. (Submitted on 9 Oct 2018)

    We use the Fermi-LAT gamma-ray observatory to search for gamma-ray emission from four nearby, debris disk-hosting main sequence stars: τ Ceti, ϵ Eridani, Fomalhaut, and Vega. For three stars (τ Ceti, Fomalhaut, and Vega), we establish upper limits that are consistent with theoretical expectations. For ϵ Eridani, we find a possible spatially coincident source with a soft energy spectrum of dN/dE∼ E −3.6. However, at this stage we are unable to rule out that this emission is due to a more extended feature in the diffuse background. In the interpretation that the emission is due to ϵ Eridani, the >100 MeV gamma-ray luminosity is ∼10^27 erg/s ≃3×10^−7 L⊙, which is ∼10^10 times the gamma-ray luminosity from the disk of the quiet Sun. We find ≲2σ evidence of source variability over a ∼7 year timescale. In the interpretation that the gamma-ray emission from ϵ Eridani itself, we consider two possible models: 1) cosmic-ray collisions with solid bodies in the debris disk which extends out ∼60 AU from the host star, and 2) emission from the stellar activity. For the former model, assuming a total disk mass consistent with infrared measurements, we find that the size distribution of bodies is steeper than expected for a collisional cascade state. If confirmed as being associated with ϵ Eridani, this would be the first indication of gamma-ray emission from the vicinity of a main sequence star other than the Sun.
    There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
    — Mark Twain, Life on the Mississippi (1883)

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