tag:blogger.com,1999:blog-10497552222192903002024-02-19T16:11:13.380-08:00The Dragon's GazeUnknownnoreply@blogger.comBlogger4023125tag:blogger.com,1999:blog-1049755222219290300.post-49105446719065222482017-12-08T08:00:00.000-08:002017-12-08T08:00:00.295-08:00A self-consistent cloud model for brown dwarfs and young giant exoplanets: comparison with photometric and spectroscopic observations<blockquote class="tr_bq">
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<b><a href="https://arxiv.org/abs/1711.11483">A self-consistent cloud model for brown dwarfs and young giant exoplanets: comparison with photometric and spectroscopic observations</a></b></div>
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Charnay et al</div>
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<b>Abstract:</b></div>
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We developed a simple, physical and self-consistent cloud model for brown dwarfs and young giant exoplanets. We compared different parametrisations for the cloud particle size, by either fixing particle radii, or fixing the mixing efficiency (parameter fsed) or estimating particle radii from simple microphysics. The cloud scheme with simple microphysics appears as the best parametrisation by successfully reproducing the observed photometry and spectra of brown dwarfs and young giant exoplanets. In particular, it reproduces the L-T transition, due to the condensation of silicate and iron clouds below the visible/near-IR photosphere. It also reproduces the reddening observed for low-gravity objects, due to an increase of cloud optical depth for low gravity. In addition, we found that the cloud greenhouse effect shifts chemical equilibriums, increasing the abundances of species stable at high temperature. This effect should significantly contribute to the strong variation of methane abundance at the L-T transition and to the methane depletion observed on young exoplanets. Finally, we predict the existence of a continuum of brown dwarfs and exoplanets for absolute J magnitude=15-18 and J-K color=0-3, due to the evolution of the L-T transition with gravity. This self-consistent model therefore provides a general framework to understand the effects of clouds and appears well-suited for atmospheric retrievals.</div>
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Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-1049755222219290300.post-83382583712502499062017-12-07T16:00:00.000-08:002017-12-07T16:00:20.373-08:00Hot Jupiters Driven by High-eccentricity Migration in Globular Clusters<blockquote class="tr_bq" style="text-align: justify;">
<b><a href="http://iopscience.iop.org/article/10.3847/1538-3881/aa9926/meta">Hot Jupiters Driven by High-eccentricity Migration in Globular Clusters</a><br /><br />Authors:</b><br /><br />Hammers et al<br /><br /><b>Abstract:</b><br /><br />Hot Jupiters (HJs) are short-period giant planets that are observed around $\sim 1 \% $ of solar-type field stars. One possible formation scenario for HJs is high-eccentricity (high-e) migration, in which the planet forms at much larger radii, is excited to high eccentricity by some mechanism, and migrates to its current orbit due to tidal dissipation occurring near periapsis. We consider high-e migration in dense stellar systems such as the cores of globular clusters (GCs), in which encounters with passing stars can excite planets to the high eccentricities needed to initiate migration. We study this process via Monte Carlo simulations of encounters with a star+planet system including the effects of tidal dissipation, using an efficient regularized restricted three-body code. HJs are produced in our simulations over a significant range of the stellar number density ${n}_{\star }$. Assuming the planet is initially on a low-eccentricity orbit with semimajor axis 1 au, for ${n}_{\star }\lesssim {10}^{3}\,{\mathrm{pc}}^{-3}$ the encounter rate is too low to induce orbital migration, whereas for ${n}_{\star }\gtrsim {10}^{6}\,{\mathrm{pc}}^{-3}$ HJ formation is suppressed because the planet is more likely ejected from its host star, tidally disrupted, or transferred to a perturbing star. The fraction of planets that are converted to HJs peaks at $\approx 2 \% $ for intermediate number densities of $\approx 4\times {10}^{4}\,{\mathrm{pc}}^{-3}$. Warm Jupiters, giant planets with periods between 10 and 100 days, are produced in our simulations with an efficiency of up to $\approx 0.5 \% $. Our results suggest that HJs can form through high-e migration induced by stellar encounters in the centers of of dense GCs, but not in their outskirts where the densities are lower.</blockquote>
Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-1049755222219290300.post-70964682042578893052017-12-07T12:00:00.000-08:002017-12-07T12:00:16.823-08:00The Most Eccentric Planet Orbiting a Giant Star<blockquote class="tr_bq" style="text-align: justify;">
<b><a href="http://iopscience.iop.org/article/10.3847/1538-3881/aa9894/meta">The Pan-Pacific Planet Search. VII. The Most Eccentric Planet Orbiting a Giant Star</a><br /><br />Authors:</b><br /><br />Wittenmyer et al<br /><br /><b>Abstract:</b><br /><br />Radial velocity observations from three instruments reveal the presence of a 4 M Jup planet candidate orbiting the K giant HD 76920. HD 76920b has an orbital eccentricity of 0.856 ± 0.009, making it the most eccentric planet known to orbit an evolved star. There is no indication that HD 76920 has an unseen binary companion, suggesting a scattering event rather than Kozai oscillations as a probable culprit for the observed eccentricity. The candidate planet currently approaches to about four stellar radii from its host star, and is predicted to be engulfed on a ~100 Myr timescale due to the combined effects of stellar evolution and tidal interactions.</blockquote>
Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-1049755222219290300.post-25884115044291245392017-12-07T08:00:00.000-08:002017-12-07T08:00:06.561-08:00Possible detection of a bimodal cloud distribution in the atmosphere of HAT-P-32Ab<blockquote class="tr_bq" style="text-align: justify;">
<b><a href="https://arxiv.org/abs/1712.00415">Possible detection of a bimodal cloud distribution in the atmosphere of HAT-P-32Ab from multi-band photometry</a><br /><br />Authors:</b><br /><br />Tregloan-Reed et al<br /><br /><b>Abstract:</b><br />We present high-precision photometry of eight separate transit events in the HAT-P-32 planetary system. One transit event was observed simultaneously by two telescopes of which one obtained a simultaneous multi-band light curve in three optical bands, giving a total of 11 transit light curves. Due to the filter selection and in conjunction with using the defocussed photometry technique we were able to obtain an extremely high precision, ground-based transit in the \textit{u}-band (350\,nm), with an rms scatter of ≈1\,mmag. All 11 transits were modelled using \textsc{prism} and \textsc{gemc}, and the physical properties of the system calculated. We find the mass and radius of the host star to be $1.182\pm 0.041\Msun$ and $1.225\pm0.015\Rsun$, respectively. For the planet we find a mass of $0.80\pm 0.14\Mjup$, a radius of $1.807\pm0.022\Rjup$ and a density of $0.126\pm0.023\pjup$. These values are consistent with those found in the literature. We also obtain a new orbital ephemeris for the system T0=BJD/TDB2454420.447187(96)+2.15000800(10)×E. We measured the transmission spectrum of HAT-P-32\,A\,b and compared it to theoretical transmission spectra. Our results indicate a bimodal cloud particle distribution consisting of Rayleigh--like haze and grey absorbing cloud particles within the atmosphere of HAT-P-32\,A\,b.</blockquote>
Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-1049755222219290300.post-76594715738385785342017-12-06T16:00:00.000-08:002017-12-06T16:00:30.816-08:00sdB Pulsating Star V391 Peg's Giant Planet Not Detected<blockquote class="tr_bq" style="text-align: justify;">
<b><a href="https://arxiv.org/abs/1711.10942">The sdB pulsating star V391 Peg and its putative giant planet revisited after 13 years of time-series photometric data</a><br /><br />Authors:</b><br /><br />Silvotti et al<br /><br /><b>Abstract:</b><br /><br />V391 Peg (alias HS2201+2610) is a subdwarf B (sdB) pulsating star that shows both p- and g-modes. By studying the arrival times of the p-mode maxima and minima through the O-C method, in a previous article the presence of a planet was inferred with an orbital period of 3.2 yr and a minimum mass of 3.2 M_Jup. Here we present an updated O-C analysis using a larger data set of 1066 hours of photometric time series (~2.5x larger in terms of the number of data points), which covers the period between 1999 and 2012 (compared with 1999-2006 of the previous analysis). Up to the end of 2008, the new O-C diagram of the main pulsation frequency (f1) is compatible with (and improves) the previous two-component solution representing the long-term variation of the pulsation period (parabolic component) and the giant planet (sine wave component). Since 2009, the O-C trend of f1 changes, and the time derivative of the pulsation period (p_dot) passes from positive to negative; the reason of this change of regime is not clear and could be related to nonlinear interactions between different pulsation modes. With the new data, the O-C diagram of the secondary pulsation frequency (f2) continues to show two components (parabola and sine wave), like in the previous analysis. Various solutions are proposed to fit the O-C diagrams of f1 and f2, but in all of them, the sinusoidal components of f1 and f2 differ or at least agree less well than before. The nice agreement found previously was a coincidence due to various small effects that are carefully analysed. Now, with a larger dataset, the presence of a planet is more uncertain and would require confirmation with an independent method. The new data allow us to improve the measurement of p_dot for f1 and f2: using only the data up to the end of 2008, we obtain p_dot_1=(1.34+-0.04)x10**-12 and p_dot_2=(1.62+-0.22)x10**-12</blockquote>
Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-1049755222219290300.post-16427718522041182572017-12-06T12:00:00.000-08:002017-12-06T12:00:21.758-08:00OGLE-2016-BLG-0613LABb: A Microlensing Planet in a Binary System<blockquote class="tr_bq" style="text-align: justify;">
<b><a href="http://iopscience.iop.org/article/10.3847/1538-3881/aa9179/meta">OGLE-2016-BLG-0613LABb: A Microlensing Planet in a Binary System</a><br /><br />Authors:</b><br /><br />Han et al<br /><br /><b>Abstract:</b><br /><br />We present the analysis of OGLE-2016-BLG-0613, for which the lensing light curve appears to be that of a typical binary-lens event with two caustic spikes but with a discontinuous feature on the trough between the spikes. We find that the discontinuous feature was produced by a planetary companion to the binary lens. We find four degenerate triple-lens solution classes, each composed of a pair of solutions according to the well-known wide/close planetary degeneracy. One of these solution classes is excluded due to its relatively poor fit. For the remaining three pairs of solutions, the most-likely primary mass is about ${M}_{1}\sim 0.7\,{M}_{\odot }$, while the planet is a super Jupiter. In all cases, the system lies in the Galactic disk, about halfway toward the Galactic bulge. However, in one of these three solution classes, the secondary of the binary system is a low-mass brown dwarf, with relative mass ratios (1:0.03:0.003), while in the two others the masses of the binary components are comparable. These two possibilities can be distinguished in about 2024 when the measured lens-source relative proper motion will permit separate resolution of the lens and source.</blockquote>
Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-1049755222219290300.post-44282237168392029112017-12-06T08:00:00.000-08:002017-12-06T08:00:02.848-08:00On the cavity of a debris disc carved by a giant planet<blockquote class="tr_bq" style="text-align: justify;">
<b><a href="https://academic.oup.com/mnras/article-abstract/473/3/3547/4411827?redirectedFrom=fulltext">On the cavity of a debris disc carved by a giant planet</a><br /><br /><br />Authors:</b><br /><br />Regály et al<br /><br /><b>Abstract:</b><br />One possible explanation of the cavity in debris discs is the gravitational perturbation of an embedded giant planet. Planetesimals passing close to a massive body are dynamically stirred resulting in a cleared region known as the chaotic zone. Theory of overlapping mean-motion resonances predicts the width of this cavity. To test whether this cavity is identical to the chaotic zone, we investigate the formation of cavities by means of collisionless N-body simulations assuming a 1.25–10 Jupiter mass planet with eccentricities of 0–0.9. Synthetic images at millimetre wavelengths are calculated to determine the cavity properties by fitting an ellipse to 14 per cent contour level. Depending on the planetary eccentricity, epl, the elliptic cavity wall rotates as the planet orbits with the same (epl less than 0.2) or half (epl greater than 0.2) period that of the planet. The cavity centre is offset from the star along the semimajor axis of the planet with a distance of d=0.1q−0.17e0.5pl d=0.1q−0.17epl0.5 in units of cavity size towards the planet's orbital apocentre, where q is the planet-to-star mass ratio. Pericentre (apocentre) glow develops for epl less than 0.05 (epl greater than 0.1), while both are present for 0.05 ≤ epl ≤ 0.1. Empirical formulae are derived for the sizes of the cavities: δacav = 2.35q0.36 and<br /> δacav=7.87q0.37e0.38pl δacav=7.87q0.37epl0.38 for epl ≤ 0.05 and epl greater 0.05, respectively. The cavity eccentricity, ecav, equals to that of the planet only for 0.3 ≤ epl ≤ 0.6. A new method based on Atacama Large Millimeter/submillimeter Array observations for estimating the orbital parameters and mass of the planet carving the cavity is also given.</blockquote>
Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-1049755222219290300.post-5767821015494706692017-12-05T16:00:00.000-08:002017-12-05T16:00:11.794-08:00Linking the Climate and Thermal Phase Curve of SuperEarth 55 Cancri e<blockquote class="tr_bq" style="text-align: justify;">
<b><a href="http://iopscience.iop.org/article/10.3847/1538-4357/aa9328/meta">Linking the Climate and Thermal Phase Curve of 55 Cancri e</a><br /><br />Authors:</b><br /><br />Hammond et al<br /><br /><b>Abstract:</b> </blockquote>
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The thermal phase curve of 55 Cancri e is the first measurement of the temperature distribution of a tidally locked super-Earth, but raises a number of puzzling questions about the planet's climate. The phase curve has a high amplitude and peak offset, suggesting that it has a significant eastward hot-spot shift as well as a large day–night temperature contrast. We use a general circulation model to model potential climates, and investigate the relation between bulk atmospheric composition and the magnitude of these seemingly contradictory features. We confirm theoretical models of tidally locked circulation are consistent with our numerical model of 55 Cnc e, and rule out certain atmospheric compositions based on their thermodynamic properties. Our best-fitting atmosphere has a significant hot-spot shift and day–night contrast, although these are not as large as the observed phase curve. We discuss possible physical processes that could explain the observations, and show that night-side cloud formation from species such as SiO from a day-side magma ocean could potentially increase the phase curve amplitude and explain the observations. We conclude that the observations could be explained by an optically thick atmosphere with a low mean molecular weight, a surface pressure of several bars, and a strong eastward circulation, with night-side cloud formation a possible explanation for the difference between our model and the observations.</blockquote>
Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-1049755222219290300.post-37751499346333220512017-12-05T12:00:00.000-08:002017-12-05T12:00:52.372-08:00The Discovery and Mass Measurement of a New Ultra-short-period Planet: EPIC 228732031b<blockquote>
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<b><a href="http://iopscience.iop.org/article/10.3847/1538-3881/aa9065/meta">The Discovery and Mass Measurement of a New Ultra-short-period Planet: EPIC 228732031b </a></b></div>
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Dai et al</div>
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<b>Abstract:</b></div>
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We report the discovery of a new ultra-short-period planet and summarize the properties of all such planets for which the mass and radius have been measured. The new planet, EPIC 228732031b, was discovered in K2 Campaign 10. It has a radius of ${1.81}_{-0.12}^{+0.16}\,{R}_{\oplus }$ and orbits a G dwarf with a period of 8.9 hr. Radial velocities obtained with Magellan/PFS and TNG/HARPS-N show evidence for stellar activity along with orbital motion. We determined the planetary mass using two different methods: (1) the "floating chunk offset" method, based only on changes in velocity observed on the same night; and (2) a Gaussian process regression based on both the radial velocity and photometric time series. The results are consistent and lead to a mass measurement of $6.5\pm 1.6\,{M}_{\oplus }$ and a mean density of ${6.0}_{-2.7}^{+3.0}$ g cm−3.</div>
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Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-1049755222219290300.post-26366992433525190392017-12-05T08:00:00.000-08:002017-12-05T08:00:10.334-08:00EPIC 246393474 b: A 5 Earth Mass super-Earth transiting a K7 V star every 6.7 hours<blockquote class="tr_bq" style="text-align: justify;">
<b><a href="https://arxiv.org/abs/1711.02097">EPIC 246393474 b: A 5-M⊕ super-Earth transiting a K7 V star every 6.7 hours</a></b> </blockquote>
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<b>Authors:</b><br /><br />Barragán et al<br /><br />Abstract:<br /><br />We report on the discovery of EPIC 246393474 b, an ultra-short-period super-Earth on a 6.7-hour orbit transiting an active K7 V star based on data from K2 campaign 12. We confirmed the planet's existence and measured its mass with a series of follow-up observations: seeing-limited MuSCAT imaging, NESSI high-resolution speckle observations, and FIES and HARPS high-precision radial-velocity monitoring. EPIC 246393474 b has a mass of 5.31±0.46 M<span style="font-size: xx-small;">⊕</span> and radius of 1.54+0.10−0.09 R<span style="font-size: xx-small;">⊕</span>, yielding a mean density of 8.00+1.83−1.45 gcm−3 and suggesting a rocky-iron composition. Models indicate that iron cannot exceed ∼70 % of the total mass. With an orbital period of only 6.7 hours, EPIC 246393474 b is the shortest-period planet known to date with a precisely determined mass.</blockquote>
Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-1049755222219290300.post-83565066039631650792017-12-04T16:00:00.000-08:002017-12-04T16:00:30.510-08:00 Whole planet coupling between climate, mantle, and core: Implications for the evolution of rocky planets<blockquote class="tr_bq" style="text-align: justify;">
<b><a href="https://arxiv.org/abs/1711.06801">Whole planet coupling between climate, mantle, and core: Implications for the evolution of rocky planets</a><br /><br />Authors:</b><br /><br />Foley et al<br /><br /><b>Abstract:</b><br /><br />Earth's climate, mantle, and core interact over geologic timescales. Climate influences whether plate tectonics can take place on a planet, with cool climates being favorable for plate tectonics because they enhance stresses in the lithosphere, suppress plate boundary annealing, and promote hydration and weakening of the lithosphere. Plate tectonics plays a vital role in the long-term carbon cycle, which helps to maintain a temperate climate. Plate tectonics provides long-term cooling of the core, which is vital for generating a magnetic field, and the magnetic field is capable of shielding atmospheric volatiles from the solar wind. Coupling between climate, mantle, and core can potentially explain the divergent evolution of Earth and Venus. As Venus lies too close to the sun for liquid water to exist, there is no long-term carbon cycle and thus an extremely hot climate. Therefore plate tectonics cannot operate and a long-lived core dynamo cannot be sustained due to insufficient core cooling. On planets within the habitable zone where liquid water is possible, a wide range of evolutionary scenarios can take place depending on initial atmospheric composition, bulk volatile content, or the timing of when plate tectonics initiates, among other factors. Many of these evolutionary trajectories would render the planet uninhabitable. However, there is still significant uncertainty over the nature of the coupling between climate, mantle, and core. Future work is needed to constrain potential evolutionary scenarios and the likelihood of an Earth-like evolution.</blockquote>
Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-1049755222219290300.post-47533367022229374132017-12-04T12:00:00.000-08:002017-12-04T12:00:24.137-08:00Hunting for a Proxima Centauri b Transit<blockquote class="tr_bq" style="text-align: justify;">
<b><a href="https://arxiv.org/abs/1711.07018">Searching for the Transit of the Earth--mass exoplanet Proxima~Centauri~b in Antarctica: Preliminary Result</a></b> </blockquote>
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<b>Authors:</b><br />
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Liu et al<br />
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Proxima~Centauri is known as the closest star from the Sun. Recently, radial velocity observations revealed the existence of an Earth--mass planet around it. With an orbital period of ∼11 days, the surface of Proxima Centauri b is temperate and might be habitable. We took a photometric monitoring campaign to search for its transit, using the Bright Star Survey Telescope at the Zhongshan Station in Antarctica. A transit--like signal appearing on September 8th, 2016, is identified tentatively. Its midtime, TC=2,457,640.1990±0.0017~HJD, is consistent with the predicted ephemeris based on RV orbit in a 1σ confidence interval. Time--correlated noise is pronounced in the light curve of Proxima Centauri, affecting detection of transits. We develop a technique, in a Gaussian process framework, to gauge the statistical significance of potential transit detection. The tentative transit signal reported here, has a confidence level of 2.5σ. Further detection of its periodic signals is necessary to confirm the planetary transit of Proxima Centauri b. We plan to monitor Proxima Centauri in next Polar night at Dome A in Antarctica, taking the advantage of continuous darkness. \citet{Kipping17} reported two tentative transit--like signals of Proxima Centauri b, observed by the Microvariability and Oscillation of Stars space Telescope in 2014 and 2015, respectively. The midtransit time of our detection is 138 minutes later than that predicted by their transit ephemeris. If all the signals are real transits, the misalignment of the epochs plausibly suggests transit timing variations of Proxima Centauri b induced by an outer planet in this system.</blockquote>
Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-1049755222219290300.post-41518381086027083152017-12-04T08:00:00.000-08:002017-12-04T08:00:13.394-08:00Ross 128b: a Temperate Exo-Earth Around a Quiet M Dwarf 11 Light Years Away<blockquote class="tr_bq" style="text-align: justify;">
<b><a href="https://arxiv.org/abs/1711.06177">A temperate exo-Earth around a quiet M dwarf at 3.4 parsecs</a><br /><br />Authors:</b><br />
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Bonfils et al<br />
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<b>Abstract:</b><br />
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The combination of high-contrast imaging and high-dispersion spectroscopy, which has successfully been used to detect the atmosphere of a giant planet, is one of the most promising potential probes of the atmosphere of Earth-size worlds. The forthcoming generation of extremely large telescopes (ELTs) may obtain sufficient contrast with this technique to detect O2 in the atmosphere of those worlds that orbit low-mass M dwarfs. This is strong motivation to carry out a census of planets around cool stars for which habitable zones can be resolved by ELTs, i.e. for M dwarfs within ∼5 parsecs. Our HARPS survey has been a major contributor to that sample of nearby planets. Here we report on our radial velocity observations of Ross 128 (Proxima Virginis, GJ447, HIP 57548), an M4 dwarf just 3.4 parsec away from our Sun. This source hosts an exo-Earth with a projected mass msini=1.35M⊕ and an orbital period of 9.9 days. Ross 128 b receives ∼1.38 times as much flux as Earth from the Sun and its equilibrium ranges in temperature between 269 K for an Earth-like albedo and 213 K for a Venus-like albedo. Recent studies place it close to the inner edge of the conventional habitable zone. An 80-day long light curve from K2 campaign C01 demonstrates that Ross~128~b does not transit. Together with the All Sky Automated Survey (ASAS) photometry and spectroscopic activity indices, the K2 photometry shows that Ross 128 rotates slowly and has weak magnetic activity. In a habitability context, this makes survival of its atmosphere against erosion more likely. Ross 128 b is the second closest known exo-Earth, after Proxima Centauri b (1.3 parsec), and the closest temperate planet known around a quiet star. The 15 mas planet-star angular separation at maximum elongation will be resolved by ELTs (> 3λ/D) in the optical bands of O2.</blockquote>
Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-1049755222219290300.post-12517919204507933172017-11-28T00:00:00.000-08:002017-11-28T00:00:06.824-08:00Rethinking the Hunt for Life<blockquote>
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Steve Desch can see the future of exoplanet research, and it’s not pretty. Imagine, he says, that astronomers use NASA’s upcoming James Webb Space Telescope to scour the atmosphere of an Earth-mass world for signs of life. Then imagine that they chase hints of atmospheric oxygen for years — before realizing that those were false positives produced by geological activity instead of living things.</div>
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Desch, an astrophysicist at Arizona State University in Tempe, and other planet hunters met from 13-17 November in Laramie, Wyoming, to plot better ways to scout for life beyond Earth. Many are starting to argue that the standard definition of habitability — having liquid water on a planet’s surface — is not the factor that should guide exoplanet exploration. Instead, the scientists say, the field should focus on the chances of detecting alien life, should it exist.</div>
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“Planets can be habitable and not have life with any impact,” Desch told researchers at the meeting.</div>
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<a href="https://www.nature.com/news/exoplanet-hunters-rethink-search-for-alien-life-1.23023">link</a>.</div>
Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-1049755222219290300.post-28502515927131832752017-11-26T20:00:00.000-08:002017-11-26T20:39:09.021-08:00Review Report on the WFIRST<blockquote>
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An independent review board for NASA’s next flagship astronomy mission concluded in its final report that the project is “not executable” without additional funding or adjustments to the spacecraft.</div>
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NASA released the report, a 65-page document in the form of a PowerPoint presentation, Nov. 22, a month after the agency published its response calling for a reduction in the proposed cost of the Wide-Field Infrared Survey Telescope (WFIRST) and changes to its management.</div>
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The report, prepared by an outside committee established by NASA called the WFIRST Independent External Technical/Management/Cost Review (WIETR), found that various changes made to WFIRST since it was proposed as the top-ranking large, or flagship, mission in the 2010 astrophysics decadal survey created cost and technical difficulties.</div>
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“After multiple discussions that set the boundary conditions, NASA HQ made a series of decisions that set the stage for an approach and mission system concept that is more complex than probably anticipated from the point of view of scope, complexity, and the concomitant risks of implementation,” the report stated.</div>
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<a href="http://spacenews.com/report-lays-out-potential-changes-to-wfirst-to-reduce-its-cost/">link</a>.</div>
Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-1049755222219290300.post-2510619954150798582017-11-23T16:00:00.000-08:002017-11-23T16:00:09.265-08:00KELT-19Ab: A P~4.6 Day Hot Jupiter Transiting a Likely Am Star with a Distant Stellar Companion<blockquote class="tr_bq" style="text-align: justify;">
<a href="https://arxiv.org/abs/1709.07010"><b>KELT-19Ab: A P~4.6 Day Hot Jupiter Transiting a Likely Am Star with a Distant Stellar Companion</b> </a></blockquote>
<blockquote class="tr_bq" style="text-align: justify;">
<b>Authors:</b><br /><br />Siverd et al<br /><br /><b>Abstract:</b><br /><br />We present the discovery of the giant planet KELT-19Ab, which transits the moderately bright (V∼9.9) A8V star TYC 764-1494-1. We confirm the planetary nature of the companion via a combination of low-precision radial velocities, which limit the mass to MP less than 4.1MJ (3σ), and a clear Doppler tomography signal, which indicates a retrograde projected spin-orbit misalignment of λ=−179.7+3.7−3.8 degrees. Global modeling indicates that the Teff=7500±110K host star has M∗=1.62+0.25−0.20M⊙ and R∗=1.83±0.10R⊙. The planet has a radius of RP=1.91±0.11RJ and receives a stellar insolation flux of ∼3.2×109ergs−1cm−2, leading to an inferred equilibrium temperature of Teq∼1935K assuming zero albedo and complete heat redistribution. With a vsinI∗=84.8±2.0kms−1, the host star is rapidly-rotating. Interestingly, its vsinI∗ is relatively low compared to other stars with similar effective temperatures, and it appears to be enhanced in metallic species such as strontium but deficient in others such as calcium, suggesting that it is likely an Am star. KELT-19A would be the first definitive detection of an Am host of a transiting planet of which we are aware. Adaptive optics observations of the system reveal the existence of a companion with late G9V/early K1V spectral type at a projected separation of ≈160AU. Radial velocity measurements indicate that this companion is bound. Most Am stars are known to have stellar companions, which are often invoked to explain the relatively slow rotation of the primary. In this case, the stellar companion is unlikely to have caused the tidal braking of the primary.</blockquote>
Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-1049755222219290300.post-36519967209779340972017-11-23T12:00:00.000-08:002017-11-23T12:00:14.293-08:00Transmission spectroscopy of the hot Jupiter TrES-3 b: Disproof of an overly large Rayleigh-like feature<blockquote class="tr_bq" style="text-align: justify;">
<b><a href="https://arxiv.org/abs/1709.06124">Transmission spectroscopy of the hot Jupiter TrES-3 b: Disproof of an overly large Rayleigh-like feature</a></b> </blockquote>
<blockquote class="tr_bq" style="text-align: justify;">
<b><br />Authors:</b><br /><br />Mackebrandt et al<br /><br /><b>Abstract:</b><br />Context. Transit events of extrasolar planets offer the opportunity to study the composition of their atmospheres. Previous work on transmission spectroscopy of the close-in gas giant TrES-3 b revealed an increase in absorption towards blue wavelengths of very large amplitude in terms of atmospheric pressure scale heights, too large to be explained by Rayleigh-scattering in the planetary atmosphere. Aims. We present a follow-up study of the optical transmission spectrum of the hot Jupiter TrES-3 b to investigate the strong increase in opacity towards short wavelengths found by a previous study. Furthermore, we aim to estimate the effect of stellar spots on the transmission spectrum. Methods. This work uses previously published long slit spectroscopy transit data of the Gran Telescopio Canarias (GTC) and published broad band observations as well as new observations in different bands from the near-UV to the near-IR, for a homogeneous transit light curve analysis. Additionally, a long-term photometric monitoring of the TrES-3 host star was performed. Results. Our newly analysed GTC spectroscopic transit observations show a slope of much lower amplitude than previous studies. We conclude from our results the previously reported increasing signal towards short wavelengths is not intrinsic to the TrES-3 system. Furthermore, the broad band spectrum favours a flat spectrum. Long-term photometric monitoring rules out a significant modification of the transmission spectrum by unocculted star spots.</blockquote>
Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-1049755222219290300.post-17814752783667337532017-11-23T08:00:00.000-08:002017-11-23T08:00:20.513-08:00The discovery of WASP-151b, WASP-153b, WASP-156b: Insights on giant planet migration and the upper boundary of the Neptunian desert<blockquote class="tr_bq" style="text-align: justify;">
<b><a href="https://arxiv.org/abs/1710.06321">The discovery of WASP-151b, WASP-153b, WASP-156b: Insights on giant planet migration and the upper boundary of the Neptunian desert</a><br />Authors:</b><br /><br />Demangeon et al </blockquote>
<blockquote class="tr_bq" style="text-align: justify;">
<b>Abstract:</b><br />To investigate the origin of the features discovered in the exoplanet population, the knowledge of exoplanets' mass and radius with a good precision is essential. In this paper, we report the discovery of three transiting exoplanets by the SuperWASP survey and the SOPHIE spectrograph with mass and radius determined with a precision better than 15 %. WASP-151b and WASP-153b are two hot Saturns with masses, radii, densities and equilibrium temperatures of 0.31^{+0.04}_{-0.03} MJ, 1.13^{+0.03}_{-0.03} RJ, 0.22^{-0.03}_{-0.02} rhoJ and 1, 290^{+20}_{-10} K, and 0.39^{+0.02}_{-0.02} MJ, 1.55^{+0.10}_{-0.08} RJ, 0.11^{+0.02}_{-0.02} rhoJ and 1, 700^{+40}_{-40} K, respectively. Their host stars are early G type stars (with magV ~ 13) and their orbital periods are 4.53 and 3.33 days, respectively. WASP-156b is a Super-Neptune orbiting a K type star (magV = 11.6) . It has a mass of 0.128^{+0.010}_{-0.009} MJ, a radius of 0.51^{+0.02}_{-0.02} RJ, a density of 1.0^{+0.1}_{-0.1} rhoJ, an equilibrium temperature of 970^{+30}_{-20} K and an orbital period of 3.83 days. WASP-151b is slightly inflated, while WASP-153b presents a significant radius anomaly. WASP-156b, being one of the few well characterised Super-Neptunes, will help to constrain the formation of Neptune size planets and the transition between gas and ice giants. The estimates of the age of these three stars confirms the tendency for some stars to have gyrochronological ages significantly lower than their isochronal ages. We propose that high eccentricity migration could partially explain this behaviour for stars hosting a short period planet. Finally, these three planets also lie close to (WASP-151b and WASP-153b) or below (WASP-156b) the upper boundary of the Neptunian desert. Their characteristics support that the ultra-violet irradiation plays an important role in this depletion of planets observed in the exoplanet population.</blockquote>
Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-1049755222219290300.post-76111381103997228472017-11-22T16:00:00.001-08:002017-11-22T16:00:21.238-08:00A Six-planet System around the Star HD 34445<blockquote class="tr_bq" style="text-align: justify;">
<b><a href="http://iopscience.iop.org/article/10.3847/1538-3881/aa8b61/meta">A Six-planet System around the Star HD 34445</a></b> </blockquote>
<blockquote class="tr_bq" style="text-align: justify;">
<b>Authors:</b><br /><br />Vogt et al </blockquote>
<blockquote class="tr_bq" style="text-align: justify;">
<b>Abstract:</b><br /><br />We present a new precision radial velocity (RV) data set that reveals a multi-planet system orbiting the G0V star HD 34445. Our 18-year span consists of 333 precision RV observations, 56 of which were previously published and 277 of which are new data from the Keck Observatory, Magellan at Las Campanas Observatory, and the Automated Planet Finder at Lick Observatory. These data indicate the presence of six planet candidates in Keplerian motion about the host star with periods of 1057, 215, 118, 49, 677, and 5700 days, and minimum masses of 0.63, 0.17, 0.1, 0.05, 0.12, and 0.38 M J, respectively. The HD 34445 planetary system, with its high degree of multiplicity, its long orbital periods, and its induced stellar RV half-amplitudes in the range 2 m s−1 lesssim K lesssim 5 m s−1 is fundamentally unlike either our own solar system (in which only Jupiter and Saturn induce significant reflex velocities for the Sun), or the Kepler multiple-transiting systems (which tend to have much more compact orbital configurations).</blockquote>
Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-1049755222219290300.post-40139858031632125512017-11-22T16:00:00.000-08:002017-11-22T16:00:31.718-08:00Chaotic quadruple secular evolution and the production of misaligned exomoons and Warm Jupiters in stellar multiples<blockquote class="tr_bq" style="text-align: justify;">
<b><a href="https://arxiv.org/abs/1710.05920">Chaotic quadruple secular evolution and the production of misaligned exomoons and Warm Jupiters in stellar multiples</a></b> </blockquote>
<blockquote class="tr_bq" style="text-align: justify;">
<b>Authors:</b><br /><br />Grishin et al<br /><br /><b>Abstract:</b><br />We study the chaotic and secular evolution of hierarchical quadruple systems in the 3+1 configuration, focusing on the evolution of mutual inclination of the inner binaries as the system undergoes coupled Lidov-Kozai (LK) oscillations. We include short-range forces (SRF; such as those due to tidal and rotational distortions) that control the eccentricity excitation of the inner binary. The evolution of mutual inclination is described, a priori, by two dimensionless parameters, $\pazocal{R}_0$, the ratio between the inner and outer LK time-scales and ϵSRF, the ratio between the SRF precession and the inner LK precession rates. We find that the chaotic zones for the mutual inclination depend mainly on $\pazocal{R}_0$, while ϵSRF controls mainly the range of eccentricity excitation. The mutual inclination evolves chaotically for $1\lesssim \pazocal{R}_0\lesssim 10$, leading to large misalignments. For $0.4 \lesssim \pazocal{R}_0 \lesssim 0.8$, the system could be weakly excited and produce bimodal distribution of mutual inclination angles. Our results can be applied to exomoons-planets in stellar binaries and Warm/Hot Jupiters in stellar triples. Such systems could develop large mutual inclination angles if the inner binary is tight enough, and also high eccentricities, depending of the strength of the short-range forces. Future detections of tilted Warm/Hot Jupiters and exomoons could put our mechanism under observational tests.</blockquote>
Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-1049755222219290300.post-23697237686467098082017-11-22T08:00:00.000-08:002017-11-22T08:00:24.220-08:00The nature of the giant exomoon candidate Kepler-1625 b-i<blockquote class="tr_bq" style="text-align: justify;">
<b><a href="https://arxiv.org/abs/1710.06209">The nature of the giant exomoon candidate Kepler-1625 b-i</a></b> </blockquote>
<blockquote class="tr_bq" style="text-align: justify;">
<b>Authors:</b><br /><br />Heller et al<br /><br /><b>Abstract:</b><br />The recent announcement of a Neptune-sized exomoon candidate around the transiting Jupiter-sized object Kepler-1625 b could indicate the presence of a hitherto unknown kind of gas giant moons, if confirmed. Three transits have been observed, allowing radius estimates of both objects. Here we investigate possible mass regimes of the transiting system that could produce the observed signatures and study them in the context of moon formation in the solar system, i.e. via impacts, capture, or in-situ accretion. The radius of Kepler-1625 b suggests it could be anything from a gas giant planet somewhat more massive than Saturn (0.4 M_Jup) to a brown dwarf (BD) (up to 75 M_Jup) or even a very-low-mass star (VLMS) (112 M_Jup ~ 0.11 M_sun). The proposed companion would certainly have a planetary mass. Possible extreme scenarios range from a highly inflated Earth-mass gas satellite to an atmosphere-free water-rock companion of about 180 M_Ear. Furthermore, the planet-moon dynamics during the transits suggest a total system mass of 17.6_{-12.6}^{+19.2} M_Jup. A Neptune-mass exomoon around a giant planet or low-mass BD would not be compatible with the common mass scaling relation of the solar system moons about gas giants. The case of a mini-Neptune around a high-mass BD or a VLMS, however, would be located in a similar region of the satellite-to-host mass ratio diagram as Proxima b, the TRAPPIST-1 system, and LHS 1140 b. The capture of a Neptune-mass object around a 10 M_Jup planet during a close binary encounter is possible in principle. The ejected object, however, would have had to be a super-Earth object, raising further questions of how such a system could have formed. In summary, this exomoon candidate is barely compatible with established moon formation theories. If it can be validated as orbiting a super-Jovian planet, then it would pose an exquisite riddle for formation theorists to solve.</blockquote>
Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-1049755222219290300.post-91387097340105389752017-11-21T16:00:00.000-08:002017-11-21T16:00:32.249-08:00Planetary Systems around Low-mass Stars Unveiled by K2<blockquote class="tr_bq" style="text-align: justify;">
<b><a href="https://arxiv.org/abs/1710.03239">Planetary Systems around Low-mass Stars Unveiled by K2</a></b> </blockquote>
<blockquote class="tr_bq" style="text-align: justify;">
<b>Authors: </b></blockquote>
<blockquote class="tr_bq" style="text-align: justify;">
Hirano et al </blockquote>
<blockquote class="tr_bq" style="text-align: justify;">
<b>Abstract: </b></blockquote>
<blockquote class="tr_bq" style="text-align: justify;">
We present the detection and follow-up observations of planetary candidates around low-mass stars observed by the {\it K2} mission. Based on light-curve analysis, adaptive-optics imaging, and optical spectroscopy at low and high resolution (including radial velocity measurements), we validate 16 planets around 12 low-mass stars observed during {\it K2} campaigns 5--10. Among the 16 planets, 12 are newly validated, with orbital periods ranging from 0.96--33 days. For one of the planets (EPIC 220621087.01) we present ground-based transit photometry, allowing us to refine the ephemerides. We also identify EPIC 220187552 as a false positive, based on the multiple stars seen in a high-resolution image and double lines in a high-resolution spectrum. Combining our {\it K2} M-dwarf planets together with the validated or confirmed planets found previously, we investigate the dependence of planet radius Rp on stellar insolation and metallicity [Fe/H]. We confirm that medium-sized planets (Rp=2−5 R⊕) seem to have experienced shrinkage --- plausibly due to photoevaporation --- and we find evidence that the shrinkage occurs at lower insolation for the coolest M dwarfs. Planets larger than ≈3 R⊕ are only found around the most metal-rich M dwarfs, and for the coolest M dwarfs (≲3500 K) there appears to be a correlation between planet size and metallicity.</blockquote>
Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-1049755222219290300.post-2041974495939996502017-11-21T12:00:00.000-08:002017-11-21T12:00:19.064-08:00Zodiacal Exoplanets in Time (ZEIT) VI: a three-planet system in the Hyades cluster including an Earth-sized planet<blockquote class="tr_bq" style="text-align: justify;">
<b><a href="https://arxiv.org/abs/1709.10328">Zodiacal Exoplanets in Time (ZEIT) VI: a three-planet system in the Hyades cluster including an Earth-sized planet</a> </b></blockquote>
<blockquote class="tr_bq" style="text-align: justify;">
<b>Authors: </b></blockquote>
<blockquote class="tr_bq" style="text-align: justify;">
Mann et al </blockquote>
<blockquote class="tr_bq" style="text-align: justify;">
<b>Abstract:</b><br />Planets in young clusters are powerful probes of the evolution of planetary systems. Here we report the discovery of three planets transiting EPIC 247589423, a late K dwarf in the Hyades (~800 Myr) cluster, and robust detection limits for additional planets in the system. The planets were identified from their K2 light curves, as part of our survey of young clusters and star forming regions. The smallest planet has a radius comparable to Earth (0.99+/-0.05 Earth radii), making it one of the few Earth-sized planets with a known, young age. The two larger planets are likely a mini-Neptune and a super-Earth, with radii of 2.91+/-0.11 and 1.45+/-0.10 Earth radii, respectively. The predicted radial velocity signals from these planets are between 0.4 and 2 m/s, achievable with modern precision RV spectrographs. Because the target star is bright (V=11.2) and has relatively low-amplitude stellar variability for a young star (2-6 mmag), EPIC 247589423 hosts the best planets known in a young open cluster for precise radial velocity follow-up, enabling a robust test of earlier claims that young planets are less dense than their older counterparts.</blockquote>
Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-1049755222219290300.post-81653335532877764772017-11-21T08:00:00.000-08:002017-11-21T08:00:39.144-08:00The fate of close-in planets: tidal or magnetic migration?<blockquote class="tr_bq" style="text-align: justify;">
<b><a href="https://arxiv.org/abs/1709.05784">The fate of close-in planets: tidal or magnetic migration?</a><br /><br />Authors: </b></blockquote>
<blockquote class="tr_bq" style="text-align: justify;">
Strugarek et al </blockquote>
<blockquote class="tr_bq" style="text-align: justify;">
<b>Abstract: </b></blockquote>
<blockquote class="tr_bq" style="text-align: justify;">
Planets in close-in orbits interact magnetically and tidally with their host stars. These interactions lead to a net torque that makes close-in planets migrate inward or outward depending on their orbital distance. We compare systematically the strength of magnetic and tidal torques for typical observed star-planet systems (T-Tauri & hot Jupiter, M dwarf & Earth-like planet, K star & hot Jupiter) based on state-of-the-art scaling-laws. We find that depending on the characteristics of the system, tidal or magnetic effects can dominate. For very close-in planets, we find that both torques can make a planet migrate on a timescale as small as 10 to 100 thousands of years. Both effects thus have to be taken into account when predicting the evolution of compact systems.</blockquote>
Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-1049755222219290300.post-30118172998608959282017-11-20T16:00:00.000-08:002017-11-20T16:00:09.426-08:00Planetary formation and water delivery in the habitable zone around solar-type stars in different dynamical environments<blockquote class="tr_bq" style="text-align: justify;">
<a href="https://arxiv.org/abs/1710.04617"><b>Planetary formation and water delivery in the habitable zone around solar-type stars in different dynamical environments</b> </a></blockquote>
<blockquote class="tr_bq" style="text-align: justify;">
<b><br />Authors:</b><br /><br />Zain et al<br /><b><br />Abstract:</b><br /><br />Aims.<br /> <br />We study the formation and water delivery of planets in the habitable zone (HZ) around solar-type stars. In particular, we study different dynamical environments that are defined by the most massive body in the system.<br /> <br />Methods.<br /> <br />First of all, a semi-analytical model was used to define the mass of the protoplanetary disks that produce each of the five dynamical scenarios of our research. Then, we made use of the same semi-analytical model to describe the evolution of embryos and planetesimals during the gaseous phase. Finally, we carried out N-body simulations of planetary accretion in order to analyze the formation and water delivery of planets in the HZ in the different dynamical environments.<br /> <br />Results.<br /> <br />Water worlds are efficiently formed in the HZ in different dynamical scenarios. In systems with a giant planet analog to Jupiter or Saturn around the snow line, super-Earths tend to migrate into the HZ from outside the snow line as a result of interactions with other embryos and accrete water only during the gaseous phase. In systems without giant planets, Earths and super-Earths with high water by mass contents can either be formed in situ in the HZ or migrate into it from outer regions, and water can be accreted during the gaseous phase and in collisions with water-rich embryos and planetesimals.<br /> <br />Conclusions.<br /> <br />The formation of planets in the HZ with very high water by mass contents seems to be a common process around Sun- like stars. Our research suggests that such planets are still very efficiently produced in different dynamical environments. Moreover, our study indicates that the formation of planets in the HZ with masses and water contents similar to those of Earth seems to be a rare process around solar-type stars in the systems under consideration.</blockquote>
Unknownnoreply@blogger.com0