## Thursday, April 30, 2015

### More on M Dwarfs as Exoplanet Host Stars

Planetary host stars: evaluating uncertainties in cool model atmospheres

Authors:

Bozhinova et al

Abstract:

M-dwarfs are emerging in the literature as promising targets for detecting low-mass, Earth-like planets. An important step in this process is to determine the stellar parameters of the M-dwarf host star as accurately as possible. Different well-tested stellar model atmosphere simulations from different groups are widely applied to undertake this task. This paper provides a comparison of different model atmosphere families to allow a better estimate of systematic errors on host-star stellar parameter introduced by the use of one specific model atmosphere family only. We present a comparison of the atlas9, marcs, phoenix and drift-phoenix model atmosphere families including the M-dwarf parameter space (Teff = 2500–4000 K, log(g) = 3.0–5.0, [M/H] = −2.5to0.5). We examine the differences in the (Tgas, pgas)-structures, in synthetic photometric fluxes and in colour indices. Model atmospheres results for higher log(g) deviate considerably less between different models families than those for lower log(g) for all Teff = 2500–4000 K examined. We compiled the broad-band synthetic photometric fluxes for all available model atmospheres (incl. M-dwarfs and brown dwarfs) for the UKIRT WFCAM ZYJHK, 2MASS JHKs and Johnson UBVRI filters, and calculated related colour indices. Synthetic colours in the IR wavelengths diverge by no more than 0.15 dex amongst all model families. For all spectral bands considered, model discrepancies in colour diminish for higher Teff atmosphere simulations. We notice differences in synthetic colours between all model families and observed example data (including Kepler 42 and GJ1214).

### The Effects of Evaporative Stellar Winds on hot Neptunes and SuperEarths

Torque on an exoplanet from an anisotropic evaporative wind

Authors:

Teyssandier et al

Abstract:

Winds from short-period Earth and Neptune mass exoplanets, driven by high energy radiation from a young star, may evaporate a significant fraction of a planet's mass. If the momentum flux from the evaporative wind is not aligned with the planet/star axis, then it can exert a torque on the planet's orbit. Using steady-state one-dimensional evaporative wind models we estimate this torque using a lag angle that depends on the product of the speed of the planet's upper atmosphere and a flow timescale for the wind to reach its sonic radius. We also estimate the momentum flux from time-dependent one-dimensional hydrodynamical simulations. We find that only in a very narrow regime in planet radius, mass and stellar radiation flux is a wind capable of exerting a significant torque on the planet's orbit. Similar to the Yarkovsky effect, the wind causes the planet to drift outward if atmospheric circulation is prograde (super-rotating) and in the opposite direction if the circulation is retrograde. A close-in super Earth mass planet that loses a large fraction of its mass in a wind could drift a few percent of its semi-major axis. While this change is small, it places constraints on the evolution of resonant pairs such as Kepler 36 b and c.

### Stellar Rotating Spots Induced Kepler Transits Time Variation and Kepler Objects of Interest

Time variation of Kepler transits induced by stellar rotating spots - a way to distinguish between prograde and retrograde motion. II. Application to KOIs

Authors:

Holczer et al

Abstract:

Mazeh, Holczer, and Shporer (2015) have presented an approach that can, in principle, use the derived transit timing variation (TTV) of some transiting planets observed by the Kepler mission to distinguish between prograde and retrograde motion of their orbits with respect to the rotation of their parent stars. The approach utilizes TTVs induced by spot-crossing events that occur when the transiting planet moves across a spot on the stellar surface, by looking for a correlation between the derived TTVs and the stellar brightness derivatives at the corresponding transits, even in data that can not resolve the spot-crossing events themselves. We present here the application of this approach to the Kepler KOIs, identifying nine systems where the photometric spot modulation is large enough and the transit timing accurate enough to allow detection of a TTV-brightness-slope correlation. Excluding KOI-1546, which has been found recently to be a stellar binary, we are left with eight hot-Jupiter systems with high sensitivity to the correlation detection. Five of those eight systems show highly significant prograde motion, including two confirmed planets (KOI-203.01 = Kepler-17b and KOI-217.01 = Kepler-71b) and three planetary candidates (KOI-883.01, KOI-895.01, and KOI-1074.01), while no system displays retrograde motion, consistent with the suggestion that planets orbiting cool stars have prograde motion. All five systems have derived impact parameter ≲0.5, and all systems with an impact parameter in that range show significant correlation, except KOI-3.01 (= Kepler-3b = HAT-P-11b) where the lack of a correlation is explained by its large stellar obliquity. Although our sample is small, these findings hint that stellar spots, or at least the larger ones, have a tendency to be located at a low latitude on the stellar disc, similar to the Sun.

## Wednesday, April 29, 2015

### HD 141569A's Protoplanetary Disk has Asymmetries, Probably Hidden Exoplanets

The Gemini NICI Planet-Finding Campaign: Asymmetries in the HD 141569 disc

Authors:

Biller et al

Abstract:

We report here the highest resolution near-IR imaging to date of the HD 141569A disc taken as part of the NICI Science Campaign. We recover 4 main features in the NICI images of the HD 141569 disc discovered in previous HST imaging: 1) an inner ring / spiral feature. Once deprojected, this feature does not appear circular. 2) an outer ring which is considerably brighter on the western side compared to the eastern side, but looks fairly circular in the deprojected image. 3) an additional arc-like feature between the inner and outer ring only evident on the east side. In the deprojected image, this feature appears to complete the circle of the west side inner ring and 4) an evacuated cavity from 175 AU inwards. Compared to the previous HST imaging with relatively large coronagraphic inner working angles (IWA), the NICI coronagraph allows imaging down to an IWA of 0.3". Thus, the inner edge of the inner ring/spiral feature is well resolved and we do not find any additional disc structures within 175 AU. We note some additional asymmetries in this system. Specifically, while the outer ring structure looks circular in this deprojection, the inner bright ring looks rather elliptical. This suggests that a single deprojection angle is not appropriate for this system and that there may be an offset in inclination between the two ring / spiral features. We find an offset of 4+-2 AU between the inner ring and the star center, potentially pointing to unseen inner companions.

### Is the G2 Cloud a Rogue Planetary Embryo?

Signatures of planets and protoplanets in the Galactic center: a clue to understand the G2 cloud?

Authors:

Mapelli et al

Abstract:

Several hundred young stars lie in the innermost parsec of our Galaxy. The super-massive black hole (SMBH) might capture planets orbiting these stars, and bring them onto nearly radial orbits. The same fate might occur to planetary embryos (PEs), i.e. protoplanets born from gravitational instabilities in protoplanetary disks. In this paper, we investigate the emission properties of rogue planets and PEs in the Galactic center. In particular, we study the effects of photoevaporation, caused by the ultraviolet background. Rogue planets can hardly be detected by current or forthcoming facilities, unless they are tidally disrupted and accrete onto the SMBH. In contrast, photoevaporation of PEs (especially if the PE is being tidally stripped) might lead to a recombination rate as high as ~10^45 s^-1, corresponding to a Brackett-gamma luminosity ~10^31 erg s^-1, very similar to the observed luminosity of the dusty object G2. We critically discuss the possibility that G2 is a rogue PE, and the major uncertainties of this model.

### More Evidence Close Binary ν Octantis has a Retrograde Circumstellar Exoplanet

Line-depth-ratio temperatures for the close binary ν Octantis: new evidence supporting the conjectured circumstellar retrograde planet

Authors:

Ramm et al

Abstract:

We explore the possibly that either star-spots or pulsations are the cause of a periodic radial velocity (RV) signal (P ∼ 400 d) from the K-giant binary ν Octantis (P ∼ 1050 d, e ∼ 0.25), alternatively conjectured to have a retrograde planet. Our study is based on temperatures derived from 22 line-depth ratios (LDRs) for ν Oct and 20 calibration stars. Empirical evidence and stability modelling provide unexpected support for the planet since other standard explanations (star-spots, pulsations and additional stellar masses) each have credibility problems. However, the proposed system presents formidable challenges to planet formation and stability theories: it has by far the smallest stellar separation of any claimed planet-harbouring binary (abin∼2.6abin∼2.6abin∼2.6 au) and an equally unbelievable separation ratio (apl/abin∼0.5apl/abin∼0.5apl/abin∼0.5), hence the necessity that the circumstellar orbit be retrograde. The LDR analysis of 215 ν Oct spectra acquired between 2001 and 2007, from which the RV perturbation was first revealed, have no significant periodicity at any frequency. The LDRs recover the original 21 stellar temperatures with an average accuracy of 45 ± 25 K. The 215 ν Oct temperatures have a standard deviation of only 4.2 K. Assuming the host primary is not pulsating, the temperatures converted to magnitude differences strikingly mimic the very stable photometric Hipparcos observations 15 years previously, implying the long-term stability of the star and demonstrating a novel use of LDRs as a photometric gauge. Our results provide substantial new evidence that conventional star-spots and pulsations are unlikely causes of the RV perturbation. The controversial system deserves continued attention, including with higher resolving-power spectra for bisector and LDR analyses.

## Tuesday, April 28, 2015

### KOI-372b: a Giant Exoplanet 17% Denser Than Earth

KOI-372: a young extrasolar system with two giant planets on wide and eccentric orbits

Authors:

Mancini et al

Abstract:

We confirm the planetary nature of KOI-372b (aka Kepler object of interest K00372.01), a giant transiting exoplanet orbiting a solar-analog G2V star. The mass of KOI-372b and the eccentricity of its orbit were accurately derived thanks to a series of precise radial velocity measurements obtained with the CAFE spectrograph mounted on the CAHA 2.2-m telescope. A simultaneous fit of the radial-velocity data and Kepler photometry revealed that KOI-372b is a dense Jupiter-like planet with a mass of Mp=3.25 Mjup and a radius of Rp=0.882 Rjup. KOI-372b is moving on a quite eccentric orbit, e=0.172, making a complete revolution around its parent star in 125.6 days. The semi-major axis of the orbit is 0.4937 au, implying that the planet is close to its habitable zone (roughly 0.5 au from it). By analysing the mid-transit times of the 12 transit events of KOI-372b recorded by the Kepler spacecraft, we found a clear transit time variation, which is attributable to the presence of a planet c in a wider orbit. We estimated that KOI-372c has a mass between 0.13 and 0.31 Mjup, also revolving on an eccentric orbit (e=0.17-0.24) in roughly 460 days, at a mean distance of 1.2 au from the host star, within the boundaries of its habitable zone. The analysis of the CAFE spectra revealed a relatively high photospheric lithium content, A(Li)=2.48 dex, suggesting that the parent star is relatively young. From a gyrochronological analysis, we estimate that the age of this planetary system is 1.0 Gyr.

### A Comprehensive Characterization of the 70 Virginis ExoPlanetary System

A Comprehensive Characterization of the 70 Virginis Planetary System

Authors:

Kane et al

Abstract:

An on-going effort in the characterization of exoplanetary systems is the accurate determination of host star properties. This effort extends to the relatively bright host stars of planets discovered with the radial velocity method. The Transit Ephemeris Refinement and Monitoring Survey (TERMS) is aiding in these efforts as part of its observational campaign for exoplanet host stars. One of the first known systems is that of 70 Virginis, which harbors a jovian planet in an eccentric orbit. Here we present a complete characterization of this system with a compilation of TERMS photometry, spectroscopy, and interferometry. We provide fundamental properties of the host star through direct interferometric measurements of the radius (1.5\% uncertainty) and through spectroscopic analysis. We combined 59 new Keck HIRES radial velocity measurements with the 169 previously published from the ELODIE, Hamilton, and HIRES spectrographs, to calculate a refined orbital solution and construct a transit ephemeris for the planet. These newly determined system characteristics are used to describe the Habitable Zone of the system with a discussion of possible additional planets and related stability simulations. Finally, we present 19 years of precision robotic photometry that constrain stellar activity and rule out central planetary transits for a Jupiter-radius planet at the 5σ level, with reduced significance down to an impact parameter of b=0.95.

### KOI-12b: a 1.43 Jupiter Radius Warm Jovian Orbiting a Fast Rotating Host Star

SOPHIE velocimetry of Kepler transit candidates XVI. Tomographic measurement of the low obliquity of KOI-12b, a warm Jupiter transiting a fast rotator

Authors:

Bourrier et al

Abstract:

We present the detection and characterization of the transiting warm Jupiter KOI-12b, first identified with Kepler with an orbital period of 17.86 days. We combine the analysis of Kepler photometry with Doppler spectroscopy and line-profile tomography of time-series spectra obtained with the SOPHIE spectrograph to establish its planetary nature and derive its properties. To derive reliable estimates for the uncertainties on the tomographic model parameters, we devised an empirical method to calculate statistically independent error bars on the time-series spectra. KOI-12b has a radius of 1.43±0.13RJup and a 3σ upper mass limit of 10MJup. It orbits a fast-rotating star (vsini⋆ = 60.0±0.9 km s−1) with mass and radius of 1.45±0.09 MSun and 1.63±0.15 RSun, located at 426±40 pc from the Earth. Doppler tomography allowed a higher precision on the obliquity to be reached by comparison with the analysis of the Rossiter-McLaughlin radial velocity anomaly, and we found that KOI-12b lies on a prograde, slightly misaligned orbit with a low sky-projected obliquity λ = 12.6−2.9+3.0∘. The properties of this planetary system, with a 11.4 magnitude host-star, make of KOI-12b a precious target for future atmospheric characterization.

## Monday, April 27, 2015

### Next Gen SETI

Author:

Garrett

Abstract:

The Search for Extra-terrestrial Intelligence (SETI) using radio telescopes is an area of research that is now more than 50 years old. Thus far, both targeted and wide-area surveys have yet to detect artificial signals from intelligent civilisations. In this paper, I argue that the incidence of co-existing intelligent and communicating civilisations is probably small in the Milky Way. While this makes successful SETI searches a very difficult pursuit indeed, the huge impact of even a single detection requires us to continue the search. A substantial increase in the overall performance of radio telescopes (and in particular future wide-field instruments such as the Square Kilometre Array – SKA), provide renewed optimism in the field. Evidence for this is already to be seen in the success of SETI researchers in acquiring observations on some of the world׳s most sensitive radio telescope facilities via open, peer-reviewed processes. The increasing interest in the dynamic radio sky, and our ability to detect new and rapid transient phenomena such as Fast Radio Bursts (FRB) is also greatly encouraging. While the nature of FRBs is not yet fully understood, I argue they are unlikely to be the signature of distant extra-terrestrial civilisations. As astronomers face a data avalanche on all sides, advances made in related areas such as advanced Big Data analytics, and cognitive computing are crucial to enable serendipitous discoveries to be made. In any case, as the era of the SKA fast approaches, the prospects of a SETI detection have never been better.

### Keck Fails to Find Evidence of Laser Sources Around 2796 Stars in Optical SETI Search

A Search for Optical Laser Emission Using Keck HIRES

Authors:

Tellis et al

Abstract:

We present a search for laser emission coming from point sources in the vicinity of 2796 stars, including 1368 Kepler Objects of Interest (KOIs) that host one or more exoplanets. We search for extremely narrow emission lines in the wavelength region between 3640 and 7890 Angstroms using the Keck 10-meter telescope and spectroscopy with high resolution (λ/Δλ = 60,000). Laser emission lines coming from non-natural sources are distinguished from natural astrophysical sources by being monochromatic and coming from an unresolved point in space. We search for laser emission located 2-7 arcsec from the 2796 target stars. The detectability of laser emission is limited by Poisson statistics of the photons and scattered light, yielding a detection threshold flux of approximately 10−2 photons m−2s−1 for typical Kepler stars and 1 photon m−2s−1 for solar-type stars within 100 light-years. Diffraction-limited lasers having a 10-meter aperture can be detected from 100 light-years away if their power exceeds 90 W, and from 1000 light-years away (Kepler planets), if their power exceeds 1 kW (from lasers located 60-200 AU, and 2000-7000 AU from the nearby and Kepler stars, respectively). We did not find any such laser emission coming from any of the 2796 target stars. We discuss the implications for the search for extraterrestrial intelligence (SETI).

### WISE Fails to Find any Type II Kardashev Supercivilizations

The Ĝ Infrared Search for Extraterrestrial Civilizations with Large Energy Supplies. III. The Reddest Extended Sources in WISE

Authors:

Griffith et al

Abstract:

Nearby Type II (galaxy-spanning) Kardashev supercivilizations would have high mid-infrared (MIR) luminosities. We have used the Wide-field Infrared Survey Explorer (WISE) to survey ~1×105 galaxies for extreme MIR emission, 103 times more galaxies than the only previous such search. We have calibrated the WISE All-sky Catalog pipeline products to improve its photometry for extended sources. We present 563 extended sources with |b|≥10 and red MIR colors, having visually vetted them to remove artifacts. No galaxies in our sample host an alien civilization reprocessing more than 85% of its starlight into the MIR, and only 50 galaxies, including Arp 220, have MIR luminosities consistent with >50% reprocessing. Ninety of these (likely) extragalactic sources have little literature presence; in most cases they are likely barely resolved galaxies or pairs of galaxies undergoing large amounts of star formation. Five are new to science and deserve further study. The Be star 48 Librae sits within a MIR nebula, and we suggest that it may be creating dust. WISE, 2MASS, and Spitzer imagery shows that IRAS 04287+6444 is consistent with a previously unnoticed, heavily extinguished cluster of young stellar objects. We identify five "passive" (i.e. red) spiral galaxies with unusually high MIR and low NUV luminosity. We search a set of optically "dark" HI galaxies for MIR emission, and find none. These 90 poorly understood sources and five anomalous passive spirals deserve follow-up via both SETI and conventional astrophysics.

### Is CoRoT candidate SRc01 E2 1066 the First Detected Binary Exoplanet???

Lewis et al

Abstract:

We discuss the detectability of gravitationally bounded pairs of gas-giant planets (which we call "binary planets") in extrasolar planetary systems that are formed through orbital instability followed by planet-planet dynamical tides during their close encounters, based on the results of N-body simulations by Ochiai, Nagasawa and Ida (Paper I). Paper I showed that the formation probability of a binary is as much as ∼10% for three giant planet systems that undergo orbital instability, and after post-capture long-term tidal evolution, the typical binary separation is 3--5 times the sum of physical radii of the planets. The binary planets are stable during main sequence lifetime of solar-type stars, if the stellarcentric semimajor axis of the binary is larger than 0.3 AU. We show that detecting modulations of transit light curves is the most promising observational method to detect binary planets. Since the likely binary separations are comparable to the stellar diameter, the shape of the transit light curve is different from transit to transit, depending on the phase of the binary's orbit. The transit durations and depth for binary planet transits are generally longer and deeper than those for the single planet case. We point out that binary planets could exist among the known inflated gas giant planets or objects classified as false positive detections at orbital radii greater than 0.3 AU, propose a binary planet explanation for the CoRoT candidate SRc01 E2 1066, and show that binary planets are likely to be present in, and could be detected using Kepler-quality data.

## Sunday, April 26, 2015

### ISO Ophiuchus 50's Clumpy Disk is Causing Apparent Stellar Variability

The young low-mass star ISO-Oph-50: Extreme variability induced by a clumpy, evolving circumstellar disk

Authors:

Scholz et al

Abstract:

ISO-Oph-50 is a young low-mass object in the ~Myr old Ophiuchus star forming region undergoing dramatic changes in its optical/near/mid-infrared brightness by 2-4 mag. We present new multi-band photometry and near-infrared spectra, combined with a synopsis of the existing literature data. Based on the spectroscopy, the source is confirmed as a mid M dwarf, with evidence for ongoing accretion. The near-infrared lightcurves show large-scale variations, with 2-4 mag amplitude in the bands IJHK, with the object generally being bluer when faint. Near its brightest state, the object shows colour changes consistent with variable extinction of dAV~7 mag. High-cadence monitoring at 3.6mu reveals quasi-periodic variations with a typical timescale of 1-2 weeks. The best explanation for these characteristics is a low-mass star seen through circumstellar matter, whose complex variability is caused by changing inhomogeneities in the inner parts of the disk. When faint, the direct stellar emission is blocked; the near-infrared radiation is dominated by scattered light. When bright, the emission is consistent with a photosphere strongly reddened by circumstellar dust. Based on the available constraints, the inhomogeneities have to be located at or beyond ~0.1 AU distance from the star. If this scenario turns out to be correct, a major portion of the inner disk has to be clumpy, structured, and/or in turmoil. In its observational characteristics, this object resembles other types of YSOs with variability caused in the inner disk. Compared to other objects, however, ISO-Oph-50 is clearly an extreme case, given the large amplitude of the brightness and colour changes combined with the erratic behaviour. ISO-Oph-50 has been near its brightest state since 2013; further monitoring is highly encouraged.

### Exoplanet Transit Polarimetry

Polarization in exoplanetary systems caused by transits, grazing transits, and starspots

Authors:

Kostogryz et al

Abstract:

We present results of numerical simulations of flux and linear polarization variations in transiting exoplanetary systems, caused by the host star disk symmetry breaking. We consider different configurations of planetary transits depending on orbital parameters. Starspot contribution to the polarized signal is also estimated. Applying the method to known systems and simulating observational conditions, a number of targets is selected where transit polarization effects could be detected. We investigate several principal benefits of the transit polarimetry, particularly, for determining orbital spatial orientation and distinguishing between grazing and near-grazing planets. Simulations show that polarization parameters are also sensitive to starspots, and they can be used to determine spot positions and sizes.

### Could Exoplanets Leave an Imprint on the Graviational Wave Background?

Stochastic Gravitational Wave Background from Exoplanets

Authors:

Ain et al

Abstract:

Recent exoplanet surveys have predicted a very large population of planetary systems in our galaxy, more than one planet per star on the average, perhaps totalling about two hundred billion. These surveys, based on electro-magnetic observations, are limited to a very small neighbourhood of the solar system and the estimations rely on the observations of only a few thousand planets. On the other hand, orbital motions of planets around stars are expected to emit gravitational waves (GW), which could provide information about the planets not accessible to electro-magnetic astronomy. The cumulative effect of the planets, with periods ranging from few hours to several years, is expected to create a stochastic GW background (SGWB). We compute the characteristic GW strain of this background based on the observed distribution of planet parameters. We also show that the integrated extragalactic background is comparable or less than the galactic background at different frequencies. Our estimate shows that the net background is significantly below the sensitivities of the proposed GW experiments in different frequency bands. However, we notice that the peak of the spectrum, at around 10−5Hz, is not too far below the proposed space based GW missions. A future space based mission may be able to observe or tightly constrain this signal, which will possibly be the only way to probe the galactic population of exoplanets as a whole.

## Saturday, April 25, 2015

### Tidal Truncation of Inclined Circumstellar and Circumbinary Disks

Tidal Truncation of Inclined Circumstellar and Circumbinary Discs in Young Stellar Binaries

Authors:

Miranda et al

Abstract:

Recent observations have shown that circumstellar and circumbinary discs in young stellar binaries are often misaligned with respect to the binary orbital plane. We analyze the tidal truncation of such misaligned discs due to torques applied to the disc at the Lindblad resonances from the tidal forcings of the binary. We consider eccentric binaries with arbitrary binary-disc inclination angles. We determine the dependence of the tidal forcing strengths on the binary parameters and show that they are complicated non-monotonic functions of eccentricity and inclination. We adopt a truncation criterion determined by the balance between resonant torque and viscous torque, and use it to calculate the outer radii of circumstellar discs and the inner radii of circumbinary discs. Misaligned circumstellar discs have systematically larger outer radii than aligned discs, and are likely to fill their Roche lobes if inclined by more than 45∘−90∘, depending on the binary mass ratio and disc viscosity parameter. Misaligned circumbinary discs generally have smaller inner radii than aligned discs, but the details depend sensitively on the binary and disc parameters.

### Circumstellar Disks in L 1495

The JCMT Gould Belt Survey: SCUBA-2 observations of circumstellar discs in L 1495

Authors:

Buckle et al

Abstract:

We present 850 and 450 μm data from the James Clerk Maxwell Telescope (JCMT) Gould Belt Survey obtained with Submillimetre Common-User Bolometer Array 2 (SCUBA-2) and characterize the dust attributes of Class I, Class II and Class III disc sources in L 1495. We detect 23 per cent of the sample at both wavelengths, with the detection rate decreasing through the Classes from I to III. The median disc mask is 1.6 × 10−3 M, and only 7 per cent of Class II sources have disc masses larger than 20 Jupiter masses. We detect a higher proportion of discs towards sources with stellar hosts of spectral type K than spectral type M. Class II discs with single stellar hosts of spectral type K have higher masses than those of spectral type M, supporting the hypothesis that higher mass stars have more massive discs. Variations in disc masses calculated at the two wavelengths suggest that there may be differences in dust opacity and/or dust temperature between discs with hosts of spectral types K to those with spectral type M.

### The Kozai-Lidov Mechanism in Hydrodynamical Disks

The Kozai-Lidov Mechanism in Hydrodynamical Disks - II. Effects of binary and disk parameters

Authors:

Fu et al

Abstract:

Martin et al. (2014b) showed that a substantially misaligned accretion disk around one component of a binary system can undergo global damped Kozai-Lidov oscillations. During these oscillations, the inclination and eccentricity of the disk are periodically exchanged. However, the robustness of this mechanism and its dependence on the system parameters were unexplored. In this paper, we use three-dimensional hydrodynamical simulations to analyze how various binary and disk parameters affect the Kozai-Lidov mechanism in hydrodynamical disks. The simulations include the effect of gas pressure and viscosity, but ignore the effects of disk self-gravity. We describe results for different numerical resolutions, binary mass ratios and orbital eccentricities, initial disk sizes, initial disk surface density profiles, disk sound speeds, and disk viscosities. We show that the Kozai-Lidov mechanism can operate for a wide range of binary-disk parameters. We discuss the applications of our results to astrophysical disks in various accreting systems.

## Friday, April 24, 2015

### NASA's NExSS: The Nexus for Exoplanet System Science

NASA is bringing together experts spanning a variety of scientific fields for an unprecedented initiative dedicated to the search for life on planets outside our solar system.

The Nexus for Exoplanet System Science, or “NExSS”, hopes to better understand the various components of an exoplanet, as well as how the planet stars and neighbor planets interact to support life.

“This interdisciplinary endeavor connects top research teams and provides a synthesized approach in the search for planets with the greatest potential for signs of life,” says Jim Green, NASA’s Director of Planetary Science. “The hunt for exoplanets is not only a priority for astronomers, it’s of keen interest to planetary and climate scientists as well.”

The study of exoplanets – planets around other stars – is a relatively new field. The discovery of the first exoplanet around a star like our sun was made in 1995. Since the launch of NASA’s Kepler space telescope six years ago, more than 1,000 exoplanets have been found, with thousands of additional candidates waiting to be confirmed. Scientists are developing ways to confirm the habitability of these worlds and search for biosignatures, or signs of life.

The key to this effort is understanding how biology interacts with the atmosphere, geology, oceans, and interior of a planet, and how these interactions are affected by the host star. This “system science” approach will help scientists better understand how to look for life on exoplanets.

### Y Class Brown Dwarfs can be Cloudless

Fingering convection and cloudless models for cool brown dwarf atmospheres

Authors:

Tremblin et al

Abstract:

This work aims to improve the current understanding of the atmospheres of brown dwarfs, especially cold ones with spectral type T and Y, whose modeling is a current challenge. Silicate and iron clouds are believed to disappear at the photosphere at the L/T transition, but cloudless models fail to reproduce correctly the spectra of T dwarfs, advocating for the addition of more physics, e.g. other types of clouds or internal energy transport mechanisms. We use a one-dimensional (1D) radiative/convective equilibrium code ATMO to investigate this issue. This code includes both equilibrium and out-of-equilibrium chemistry and solves consistently the PT structure. Included opacity sources are H2-H2, H2-He, H2O, CO, CO2, CH4, NH3, K, Na, and TiO, VO if they are present in the atmosphere. We show that the spectra of Y dwarfs can be accurately reproduced with a cloudless model if vertical mixing and NH3 quenching are taken into account. T dwarf spectra still have some reddening in e.g. J - H compared to cloudless models. This reddening can be reproduced by slightly reducing the temperature gradient in the atmosphere. We propose that this reduction of the stabilizing temperature gradient in these layers, leading to cooler structures, is due to the onset of fingering convection, triggered by the destabilizing impact of condensation of very thin dust.

### J061213.85-303612.5: a new T Class Brown Dwarf Binary With a 11 AU Separation

WISE J061213.85-303612.5: a new T-dwarf binary candidate

Authors:

Huélamo et al

Abstract:

T and Y-dwarfs are among the coolest and least luminous objects detected, and they can help to understand the properties of giant planets. Their multiplicity properties can shed light on the formation process. We observed a sample six T dwarfs and one L9 dwarf with the Laser Guide Star (LGS) and NAOS-CONICA, the adaptive optics (AO) facility, and the near infrared camera at the ESO Very Large Telescope. From the seven observed objects, we have identified a subarcsecond binary system, WISE~J0612-3036, composed of two similar components with spectral types of T6. We measure a separation of ρ = 350±5 mas and a position angle of PA=235±1∘. Using the mean absolute magnitudes of T6 dwarfs in the 2MASS JHKs bands, we estimate a distance of d=31±6 pc and derive a projected separation of ρ = 11±2 au. Another target, WISE J2255-3118, shows a very faint object at 1.3 arcsec in the Ks image. The object is marginally detected in H, and we derive a near infrared color of H−Ks> 0.1\,mag. HST/WFC3 public archival data reveals that the companion candidate is an extended source.Together with the derived color, this suggests that the source is most probably a background galaxy. The five other sources are apparently single, with 3-σ sensitivity limits between H=19-21 for companions at separations ≥ 0.5 arcsec. WISE 0612-3036 is probably a new T-dwarf binary composed of two T6 dwarfs. As in the case of other late T-dwarf binaries, it shows a mass ratio close to 1, although its projected separation, ∼11 au, is larger than the average (∼ 5 au). Additional observations are needed to confirm that the system is bound.

### DE0630-18B: a new Brown Dwarf in a 3 year Orbit

Astrometric planet search around southern ultracool dwarfs III. Discovery of a brown dwarf in a 3-year orbit around DE0630-18

Authors:

Sahlmann et al

Abstract:

Using astrometric measurements obtained with the FORS2/VLT camera, we are searching for low-mass companions around 20 nearby ultracool dwarfs. With a single-measurement precision of 0.1 milli-arcseconds, our survey is sensitive to a wide range of companion masses from planetary companions to binary systems. Here, we report the discovery and orbit characterisation of a new ultracool binary at a distance of 19.5 pc from Earth that is composed of the M8.5-dwarf primary DE0630-18 and a substellar companion. The nearly edge-on orbit is moderately eccentric (e=0.23) with an orbital period of 1120 d, which corresponds to a relative separation in semimajor axis of approximately 1.1 AU. We obtained a high-resolution optical spectrum with UVES/VLT and measured the system's heliocentric radial velocity. The spectrum does not exhibit lithium absorption at 670.8 nm, indicating that the system is not extremely young. A preliminary estimate of the binary's physical parameters tells us that it is composed of a primary at the stellar-substellar limit and a massive brown-dwarf companion. DE0630-18 is a new very low-mass binary system with a well-characterised orbit.

## Thursday, April 23, 2015

### NASA Goddard Adapting Climate Model for Exoplanet Simulations

The hunt for life beyond the Solar System is gaining new partners: NASA climatologists. After more than 30 years of studying Earth, a team at the NASA Goddard Institute for Space Studies (GISS) in New York will adapt its global climate model to simulate conditions on potentially habitable exoplanets. The effort is part of a broader push to identify Earth-like worlds that NASA will launch on 20 April at a meeting in Washington DC.

Already, the agency’s space-based Kepler telescope has pinpointed more than 1,000 alien planets by observing the brief interruption of starlight that signals a planet passing in front of its parent star. At least five of these planets are similar in size to Earth and located in the ‘habitable zone’, where liquid water could persist. The next step would be to detect light passing through exoplanet atmospheres, which could hold clues to conditions on these distant worlds.

### The Effects of PhotoEvaporation on Giant Exoplanet Orbits

The link between disc dispersal by photoevaporation and the semi-major axis distribution of exoplanets

Authors:

Ercolano et al

Abstract:

We investigate the influence of photoevaporation of protoplanetary discs on the final distribution of exoplanets semi-major axis distances. We model giant planet migration in viscous discs affected by photoevaporation driven by either pure EUV or soft X-ray radiation (XEUV). We show that the final exoplanet distributions are strongly dependant on the choice of the photoevaporation model. In particular, we find that XEUV is more efficient than pure EUV radiation at parking planets at approximately 1-2 AU distance from their central star, hence roughly reproducing the observed peak in the exoplanets semi-major axis distributions. We note however that a more quantitative comparison with the observations is hindered by the oversimplified treatment of planetary accretion, which severely affects migration rates. For this reason, caution should be used when using these models to constrain details of disc clearing and/or migration from the observations. Nevertheless our results indicate that disc dispersal by photoevaporation may be the main driver of the features in the exoplanets semi-major axis distribution observed by recent surveys.

### The Odd Hot Jupiters CoRoT-28b and Comet-like (?) CoRoT-29b Orbit Giant Stars

Transiting exoplanets from the CoRoT space mission XXVIII. CoRoT-28b, a planet orbiting an evolved star, and CoRoT-29b, a planet showing an asymmetric transit

Authors:

Cabrera et al

Abstract:

Context.

We present the discovery of two transiting extrasolar planets by the satellite CoRoT.

Aims.

We aim at a characterization of the planetary bulk parameters, which allow us to further investigate the formation and evolution of the planetary systems and the main properties of the host stars.

Methods.

We used the transit light curve to characterize the planetary parameters relative to the stellar parameters. The analysis of HARPS spectra established the planetary nature of the detections, providing their masses. Further photometric and spectroscopic ground-based observations provided stellar parameters (log g,Teff,v sin i) to characterize the host stars. Our model takes the geometry of the transit to constrain the stellar density into account, which when linked to stellar evolutionary models, determines the bulk parameters of the star. Because of the asymmetric shape of the light curve of one of the planets, we had to include the possibility in our model that the stellar surface was not strictly spherical.

Results.

We present the planetary parameters of CoRoT-28b, a Jupiter-sized planet (mass 0.484+/-0.087MJup; radius 0.955+/-0.066RJup) orbiting an evolved star with an orbital period of 5.208 51 +/- 0.000 38 days, and CoRoT-29b, another Jupiter-sized planet (mass 0.85 +/- 0.20MJup; radius 0.90 +/- 0.16RJup) orbiting an oblate star with an orbital period of 2.850 570 +/- 0.000 006 days. The reason behind the asymmetry of the transit shape is not understood at this point.

Conclusions.

These two new planetary systems have very interesting properties and deserve further study, particularly in the case of the star CoRoT-29.

### Inhomogeneous Atmospheric Reflection in Three hot Jupiters: Kepler-7, Kepler-12 & Kepler-41

Studying atmosphere-dominated hot Jupiter Kepler phase curves: Evidence that inhomogeneous atmospheric reflection is common

Authors:

Shporer et al

Abstract:

We identify 3 Kepler transiting planet systems, Kepler-7, Kepler-12, and Kepler-41, whose orbital phase-folded light curves are dominated by planetary atmospheric processes including thermal emission and reflected light, while the impact of non-atmospheric (i.e. gravitational) processes, including beaming (Doppler boosting) and tidal ellipsoidal distortion, is negligible. Therefore, those systems allow a direct view of their atmospheres without being hampered by the approximations used in the inclusion of both atmospheric and non-atmospheric processes when modeling the phase curve shape. Here we analyze Kepler-12b and Kepler-41b atmosphere based on their Kepler phase curve, while the analysis of Kepler-7b was presented elsewhere. The model we used efficiently computes reflection and thermal emission contributions to the phase curve, including inhomogeneous atmospheric reflection due to longitudinally varying cloud coverage. We confirm Kepler-12b and Kepler-41b show a westward phase shift between the brightest region on the planetary surface and the substellar point, similar to Kepler-7b. We find that reflective clouds located on the west side of the substellar point can explain the phase shift. The existence of inhomogeneous atmospheric reflection in all 3 of our targets, selected due to their atmosphere-dominated Kepler phase curve, suggests this phenomenon is common. Therefore it is likely to be present also in planetary phase curves that do not allow a direct view of the planetary atmosphere as they contain additional orbital processes. We discuss the implications of a bright-spot shift on the analysis of phase curves where both atmospheric and gravitational processes appear. We also discuss the potential detection of non-transiting but otherwise similar planets, whose mass is too small to show a gravitational photometric signal but their atmospheric signal is detectable.

## Wednesday, April 22, 2015

### Tau Ceti's Exoplanets Have Only Been in the Habitable Zone for 1 Billion Years

As the search continues for Earth-size planets orbiting at just the right distance from their star, a region termed the habitable zone, the number of potentially life-supporting planets grows. In two decades we have progressed from having no extrasolar planets to having too many to search. Narrowing the list of hopefuls requires looking at extrasolar planets in a new way. Applying a nuanced approach that couples astronomy and geophysics, Arizona State University researchers report that from that long list we can cross off cosmic neighbor Tau Ceti.

The Tau Ceti system, popularized in several fictional works, including Star Trek, has long been used in science fiction, and even popular news, as a very likely place to have life due to its proximity to Earth and the star's sun-like characteristics. Since December 2012 Tau Ceti has become even more appealing, thanks to evidence of possibly five planets orbiting it, with two of these - Tau Ceti e and f - potentially residing in the habitable zone.

Using the chemical composition of Tau Ceti, the ASU team modeled the star's evolution and calculated its habitable zone. Although their data confirms that two planets (e and f) may be in the habitable zone it doesn't mean life flourishes or even exists there.

"Planet e is in the habitable zone only if we make very generous assumptions. Planet f initially looks more promising, but modeling the evolution of the star makes it seem probable that it has only moved into the habitable zone recently as Tau Ceti has gotten more luminous over the course of its life," explains astrophysicist Michael Pagano, ASU postdoctoral researcher and lead author of the paper appearing in the Astrophysical Journal. The collaboration also included ASU astrophysicists Patrick Young and Amanda Truitt and mineral physicist Sang-Heon (Dan) Shim.

Based upon the team's models, planet f has likely been in the habitable zone much less than 1 billion years. This sounds like a long time, but it took Earth's biosphere about 2 billion years to produce potentially detectable changes in its atmosphere. A planet that entered the habitable zone only a few hundred million years ago may well be habitable and even inhabited, but not have detectable biosignatures.

According to Pagano, he and his collaborators didn't pick Tau Ceti "hoping, wanting, or thinking" it would be a good candidate to look for life, but for the idea that these might be truly alien new worlds.

Tau Ceti has a highly unusual composition with respect to its ratio of magnesium and silicon, which are two of the most important rock forming minerals on Earth. The ratio of magnesium to silicon in Tau Ceti is 1.78, which is about 70% more than our sun.

The astrophysicists looked at the data and asked, "What does this mean for the planets?"

The paper is available here.

### Capture and Evolution of Planetesimals in Circum Gas Giant Disks

Capture and Evolution of Planetesimals in Circumjovian Disks

Authors:

D'Angelo et al

Abstract:

We study the evolution of planetesimals in evolved gaseous disks, which orbit a solar-mass star and harbor a Jupiter-mass planet at a_p~5AU. The gas dynamics is modeled with a three-dimensional hydrodynamics code that employes nested-grids and achieves a resolution of one Jupiter's radius in the circumplanetary disk. The code models solids as individual particles. Planetesimals are subjected to gravitational forces by the star and the planet, drag force by the gas, disruption via ram pressure, and mass loss through ablation. The mass evolution of solids is calculated self-consistently with their temperature, velocity, and position. We consider icy and icy/rocky bodies of radius 0.1-100km, initially deployed on orbits around the star within a few Hill radii (Rhill) of the planet's orbit. Planetesimals are scattered inward, outward, and toward disk regions of radius much greater than a_p. Scattering can relocate significant amounts of solids, provided that regions |r-a_p|~ 3Rhill are replenished with planetesimals. Scattered bodies can be temporarily captured on planetocentric orbits. Ablation consumes nearly all solids at gas temperatures greater than ~220K. Super-keplerian rotation around and beyond the outer edge of the gas gap can segregate less than ~0.1km bodies, producing solid gap edges at size-dependent radial locations. Capture, break-up, and ablation of solids result in a dust-laden circumplanetary disk with low surface densities of km-size planetesimals, implying relatively long timescales for satellite formation. After a giant planet acquires most of its mass, accretion of solids is unlikely to alter significantly its heavy-element content. The luminosity generated by solids' accretion can be of a similar order of magnitude to the contraction luminosity.

### What Does it Take to Form a Mars Mass Icy ExoMoon Around Super Jovians?

Conditions for water ice lines and Mars-mass exomoons around accreting super-Jovian planets at 1 - 20 AU from Sun-like stars

Authors:

Heller et al

Abstract:

Exomoon detections might be feasible with NASA's Kepler or ESA's upcoming PLATO mission or the ground-based E-ELT. To use observational resources most efficiently we need to know where the largest, most easily detected moons can form. We explore the possibility of large exomoons by following the movement of water (H2O) ice lines in the accretion disks around young super-Jovian planets. We want to know how different heating sources in those disks affect the H2O ice lines. We simulate 2D rotationally symmetric accretion disks in hydrostatic equilibrium around super-Jovian exoplanets. The energy terms in our semi-analytical model -- (1) viscous heating, (2) planetary illumination, (3) accretional heating, and (4) stellar illumination -- are fed by precomputed planet evolution tracks. We consider planets accreting 1 to 12 Jupiter masses at distances between 1 and 20 AU to a Sun-like star. Accretion disks around Jupiter-mass planets closer than ~4.5 AU to Sun-like stars do not feature H2O ice lines, but the most massive super-Jovians can form icy satellites as close as ~3 AU to Sun-like stars. Super-Jovian planets forming beyond ~5 AU can host Mars-mass moons. We study a broad range of disk parameters for planets at 5.2 AU and find that the H2O ice lines are universally between ~15 and 30 Jupiter radii when the last generation of moons is forming. If the abundant population of super-Jovian planets at ~1 AU formed in situ, then they should lack giant icy moons because their disks did not host H2O ice in the final stages of accretion. In the more likely case that these planets migrated to their current locations from beyond a few AU, they might be orbited by large, H2O-rich moons. In this case, Mars-mass ocean moons might be common in the stellar habitable zones. Future exomoon searches can provide powerful constraints on the formation and migration history of giant exoplanets.

### No Exomoons Found Around 41 Kepler Exoplanets

The Hunt for Exomoons with Kepler (HEK): V. A Survey of 41 Planetary Candidates for Exomoons

Authors:

Kipping et al

Abstract:

We present a survey of 41 Kepler Objects of Interest (KOIs) for exomoons using Bayesian photodynamics, more than tripling the number of KOIs surveyed with this technique. We find no compelling evidence for exomoons although thirteen KOIs yield spurious detections driven by instrumental artifacts, stellar activity and/or perturbations from unseen bodies. Regarding the latter, we find seven KOIs exhibiting greater than 5 sigma evidence of transit timing variations, including the 'mega-Earth' Kepler-10c, likely indicating an additional planet in that system. We exploit the moderately large sample of 57 unique KOIs surveyed to date to infer several useful statistics. For example, although there is a diverse range in sensitivities, we find that we are sensitive to Pluto-Charon mass-ratio systems for ~40% of KOIs studied and Earth-Moon mass-ratios for 1 in 8 cases. In terms of absolute mass, our limits probe down to 1.7 Ganymede masses, with a sensitivity to Earth-mass moons for 1 in 3 cases studied and to the smallest moons capable of sustaining an Earth-like atmosphere (0.3 Earth masses) for 1 in 4. Despite the lack of positive detections to date, we caution against drawing conclusions yet, since our most interesting objects remain under analysis. Finally, we point out that had we searched for the photometric transit signals of exomoons alone, rather than using photodynamics, we estimate that 1 in 4 KOIs would have erroneously been concluded to harbor exomoons due to residual time correlated noise in the Kepler data, posing a serious problem for alternative methods.

## Tuesday, April 21, 2015

### SuperEarths Closer Than One AU Cannot Form in Situ

A reassessment of the in situ formation of close-in super-Earths

Authors:

Ogihara et al

Abstract:

A large fraction of stars host one or multiple close-in super-Earth planets. There is an active debate about whether these planets formed in situ or at greater distances from the central star and migrated to their current position. It has been shown that part of their observed properties (e.g., eccentricity distribution) can be reproduced by N-body simulations of in situ formation starting with a population of protoplanets of high masses and neglecting the effects of the disk gas. We plan to reassess the in situ formation of close-in super-Earths through more complete simulations. We performed N-body simulations of a population of small planetary embryos and planetesimals that include the effects of disk-planet interactions (e.g., eccentricity damping, type I migration). In addition, we also consider the accretion of a primitive atmosphere from a protoplanetary disk. We find that planetary embryos grow very quickly well before the gas dispersal, and thus undergo rapid inward migration, which means that one cannot neglect the effects of a gas disk when considering the in-situ formation of close-in super-Earths. Owing to their rapid inward migration, super-Earths reach a compact configuration near the disk's inner edge whose distribution of orbital parameters matches the observed close-in super-Earths population poorly. On the other hand, simulations including eccentricity damping, but no type I migration, reproduce the observed distributions better. Including the accretion of an atmosphere does not help reproduce the bulk architecture of observations. Interestingly, we find that the massive embryos can migrate inside the disk edge while capturing only a moderately massive hydrogen/helium atmosphere. By this process they avoid becoming giant planets. The bulk of close-in super-Earths cannot form in situ, unless type I migration is suppressed in the entire disk inside 1 AU.

### How to Detect Volcanic Activity on Exoplanets

Transient Sulfate Aerosols as a Signature of Exoplanet Volcanism

Authors:

Misra et al

Abstract:

Geological activity is thought to be important for the origin of life and for maintaining planetary habitability. We show that transient sulfate aerosols could be a signature of exoplanet volcanism, and therefore a geologically active world. A detection of transient aerosols, if linked to volcanism, could thus aid in habitability evaluations of the exoplanet. On Earth, subduction-induced explosive eruptions inject SO2 directly into the stratosphere, leading to the formation of sulfate aerosols with lifetimes of months to years. We demonstrate that the rapid increase and gradual decrease in sulfate aerosol loading associated with these eruptions may be detectable in transit transmission spectra with future large-aperture telescopes, such as the James Webb Space Telescope (JWST) and European Extremely-Large Telescope (E-ELT) for a planetary system at a distance of 10 pc, assuming an Earth-like atmosphere, bulk composition, and size. Specifically, we find that a S/N of 12.1 and 7.1 could be achieved with E-ELT (assuming photon-limited noise) for an Earth-analog orbiting a Sun-like star and M5V star, respectively, even without multiple transits binned together. We propose that the detection of this transient signal would strongly suggest an exoplanet volcanic eruption, if potential false positives such as dust storms or bolide impacts can be ruled out. Furthermore, because scenarios exist in which O2 can form abiotically in the absence of volcanic activity, a detection of transient aerosols that can be linked to volcanism, along with a detection of O2, would be a more robust biosignature than O2 alone.

### EPIC 201637175b: a Disintegrating Terrestrial Exoplanet With a Comet-like Head and Tail

The K2-ESPRINT Project I: Discovery of the Disintegrating Rocky Planet with a Cometary Head and Tail EPIC 201637175b

Authors:

Sanchis-Ojeda et al

Abstract:

We present the discovery of a transiting exoplanet candidate in the K2 Field-1 with an orbital period of 9.1457 hours: EPIC 201637175b. The highly variable transit depths, ranging from ∼0\% to 1.3\%, are suggestive of a planet that is disintegrating via the emission of dusty effluents. We characterize the host star as an M-dwarf with Teff≃3800. We have obtained ground-based transit measurements with several 1-m class telescopes and with the GTC. These observations (1) improve the transit ephemeris; (2) confirm the variable nature of the transit depths; (3) indicate variations in the transit shapes; and (4) demonstrate clearly that at least on one occasion the transit depths were significantly wavelength dependent. The latter three effects tend to indicate extinction of starlight by dust rather than by any combination of solid bodies. The K2 observations yield a folded light curve with lower time resolution but with substantially better statistical precision compared with the ground-based observations. We detect a significant bump' just after the transit egress, and a less significant bump just prior to transit ingress. We interpret these bumps in the context of a planet that is not only likely streaming a dust tail behind it, but also has a more prominent leading dust trail that precedes it. This effect is modeled in terms of dust grains that can escape to beyond the planet's Hill sphere and effectively undergo `Roche lobe overflow', even though the planet's surface is likely underfilling its Roche lobe by a factor of 2.

## Monday, April 20, 2015

### Modeling the Kepler Objects of Interest

Uniform Modeling of KOIs: MCMC Data Release Notes

Authors:

Rowe et al

Abstract:

The Kepler Mission used a 0.95-m aperture space-based telescope to continuously observe more than 150 000 stars for 4 years. We model and analyze most KOIs listed at the Exoplanet Archive using the Kepler data. This document describes data products related to the reported planetary parameters and uncertainties for the Kepler Objects of Interest (KOIs) based on a Markov-Chain-Monte- Carlo (MCMC) analysis. Reported parameters, uncertainties and data products can be found at the NASA Exoplanet Archive

### The Implications of a Simulation's fit to the Kepler Exoplanet Orbit Data

The statistical mechanics of planet orbits

Authors:

Tremaine et al

Abstract:

The final "giant-impact" phase of terrestrial planet formation is believed to begin with a large number of planetary "embryos" on nearly circular, coplanar orbits. Mutual gravitational interactions gradually excite their eccentricities until their orbits cross and they collide and merge; through this process the number of surviving bodies declines until the system contains a small number of planets on well-separated, stable orbits. In this paper we explore a simple statistical model for the orbit distribution of planets formed by this process, based on the sheared-sheet approximation and the ansatz that the planets explore uniformly all of the stable region of phase space. The model provides analytic predictions for the distribution of eccentricities and semimajor axis differences, correlations between orbital elements of nearby planets, and the complete N-planet distribution function, in terms of a single parameter that is determined by the planetary masses. The predicted properties are generally consistent with both N-body simulations and the Kepler catalog of extrasolar planets. A similar model may apply to the orbits of giant planets if these orbits are determined mainly by dynamical evolution after the planets have formed and the gas disk has disappeared.

### Where do Circumbinary Exoplanets Form?

Birth Locations of the Kepler Circumbinary Planets

Authors:

Silsbee et al

Abstract:

The Kepler mission has discovered about a dozen circumbinary planetary systems, all containing planets on ~ 1 AU orbits. We place bounds on the locations in the circumbinary protoplanetary disk, where these planets could have formed through collisional agglomeration starting from small (km-sized or less) planetesimals. We first present a model of secular planetesimal dynamics that accounts for the (1) perturbation due to the eccentric precessing binary, as well as the (2) gravity and (3) gas drag from a precessing eccentric disk. Their simultaneous action leads to rich dynamics, with (multiple) secular resonances emerging in the disk. We derive analytic results for size-dependent planetesimal eccentricity, and demonstrate the key role of the disk gravity for circumbinary dynamics. We then combine these results with a simple model for collisional outcomes and find that in systems like Kepler 16, planetesimal growth starting with 10-100 m planetesimals is possible outside a few AU. The exact location exterior to which this happens is sensitive to disk eccentricity, density and precession rate, as well as to the size of the first generation of planetesimals. Strong perturbations from the binary in the inner part of the disk, combined with a secular resonance at a few AU inhibit the growth of km-sized planetesimals within 2 - 4 AU of the binary. In situ planetesimal growth in the Kepler circumbinary systems is possible only starting from large (few-km-sized) bodies in a low-mass disk with surface density less than 500 g/cm^2 at 1 AU.

## Sunday, April 19, 2015

### Magnetic Activity and Asteroseismology of τ Bootis A

The GAPS Programme with HARPS-N at TNG. VII. Putting exoplanets in the stellar context: magnetic activity and asteroseismology of τ Bootis A

Authors:

Borsa et al

Abstract:

Aims.

We observed the τ Boo system with the HARPS-N spectrograph to test a new observational strategy aimed at jointly studying asteroseismology, the planetary orbit, and star-planet magnetic interaction.

Methods.

We collected high-cadence observations on 11 nearly consecutive nights and for each night averaged the raw FITS files using a dedicated software. In this way we obtained spectra with a high signal-to-noise ratio, used to study the variation of the CaII H&K lines and to have radial velocity values free from stellar oscillations, without losing the oscillations information. We developed a dedicated software to build a new custom mask that we used to refine the radial velocity determination with the HARPS-N pipeline and perform the spectroscopic analysis.

Results.

We updated the planetary ephemeris and showed the acceleration caused by the stellar binary companion. Our results on the stellar activity variation suggest the presence of a high-latitude plage during the time span of our observations. The correlation between the chromospheric activity and the planetary orbital phase remains unclear. Solar-like oscillations are detected in the radial velocity time series: we estimated asteroseismic quantities and found that they agree well with theoretical predictions. Our stellar model yields an age of 0.9±0.5 Gyr for τ Boo and further constrains the value of the stellar mass to 1.38±0.05 M⊙.

### Studying the Host Star-Disk Connection of GM Aur

Using FUV to IR Variability to Probe the Star-Disk Connection in the Transitional Disk of GM Aur

Authors:

Ingleby et al

Abstract:

We analyze 3 epochs of ultraviolet (UV), optical and near-infrared (NIR) observations of the Taurus transitional disk GM Aur using the Hubble Space Telescope Imaging Spectrograph (STIS) and the Infrared Telescope Facility SpeX spectrograph. Observations were separated by one week and 3 months in order to study variability over multiple timescales. We calculate accretion rates for each epoch of observations using the STIS spectra and find that those separated by one week had similar accretion rates (~1E-8 solar masses/yr) while the epoch obtained 3 months later had a substantially lower accretion rate (~4E-9 solar masses/yr). We find that the decline in accretion rate is caused by lower densities of material in the accretion flows, as opposed to a lower surface coverage of the accretion columns. During the low accretion rate epoch we also observe lower fluxes at both far UV (FUV) and IR wavelengths, which trace molecular gas and dust in the disk, respectively. We find that this can be explained by a lower dust and gas mass in the inner disk. We attribute the observed variability to inhomogeneities in the inner disk, near the corotation radius, where gas and dust may co-exist near the footprints of the magnetospheric flows. These FUV--NIR data offer a new perspective on the structure of the inner disk, the stellar magnetosphere, and their interaction.

### RAVE as a Gaia Precursor

RAVE as a Gaia precursor: what to expect from the Gaia RVS?

Authors:

Stenmetz

Abstract:

The Radial Velocity Experiment (RAVE) is a large wide-field spectroscopic stellar survey of the Milky Way. Over the period 2003-2013, 574,630 spectra for 483,330 stars have been amassed at a resolution of R=7500 in the Ca-triplet region of 8410-8795\AA. Wavelength coverage and resolution are thus comparable to that anticipated from the Gaia RVS. Derived data products of RAVE include radial velocities, stellar parameters, chemicals abundances for Mg, Al, Si, Ca, Ti, Fe, and Ni, and absorption measures based on the diffuse interstellar bands (DIB) at 8620\AA. Since more than 290000 RAVE targets are drawn from the Tycho-2 catalogue, RAVE will be an interesting prototype for the anticipated full Gaia data releases, in particular when combined with the early Gaia data releases, which contain astrometry but not yet stellar parameters and abundances.

## Saturday, April 18, 2015

### LkCa 15's Protoplanetary Disk is Chemically Rich

An Unbiased 1.3 mm Emission Line Survey of the Protoplanetary Disk Orbiting LkCa 15

Authors:

Punzi et al

Abstract:

The outer ( greater than30 AU) regions of the dusty circumstellar disk orbiting the ~2-5 Myr-old, actively accreting solar analog LkCa 15 are known to be chemically rich, and the inner disk may host a young protoplanet within its central cavity. To obtain a complete census of the brightest molecular line emission emanating from the LkCa 15 disk over the 210-270 GHz (1.4 - 1.1 mm) range, we have conducted an unbiased radio spectroscopic survey with the Institute de Radioastronomie Millimetrique (IRAM) 30 meter telescope. The survey demonstrates that, in this spectral region, the most readily detectable lines are those of CO and its isotopologues 13CO and C18O, as well as HCO+, HCN, CN, C2H, CS, and H2CO. All of these species had been previously detected in the LkCa 15 disk; however, the present survey includes the first complete coverage of the CN (2-1) and C2H (3-2) hyperfine complexes. Modeling of these emission complexes indicates that the CN and C2H either reside in the coldest regions of the disk or are subthermally excited, and that their abundances are enhanced relative to molecular clouds and young stellar object environments. These results highlight the value of unbiased single-dish line surveys in guiding future high resolution interferometric imaging of disks.

### High-resolution Imaging of Herbig Ae/Be Stellar Disks

High-resolution 25 μm imaging of the disks around Herbig Ae/Be stars

Authors:

Honda et al

Abstract:

We imaged circumstellar disks around 22 Herbig Ae/Be stars at 25 \mu m using Subaru/COMICS and Gemini/T-ReCS. Our sample consists of equal numbers of objects belonging to the two categories defined by Meeus et al. (2001); 11 group I (flaring disk) and II (at disk) sources. We find that group I sources tend to show more extended emission than group II sources. Previous studies have shown that the continuous disk is hard to be resolved with 8 meter class telescopes in Q-band due to the strong emission from the unresolved innermost region of the disk. It indicates that the resolved Q-band sources require a hole or gap in the disk material distribution to suppress the contribution from the innermost region of the disk. As many group I sources are resolved at 25 \mu m, we suggest that many, not all, group I Herbig Ae/Be disks have a hole or gap and are (pre-)transitional disks. On the other hand, the unresolved nature of many group II sources at 25 \mu m supports that group II disks have continuous at disk geometry. It has been inferred that group I disks may evolve into group II through settling of dust grains to the mid-plane of the proto-planetary disk. However, considering growing evidence for the presence of a hole or gaps in the disk of group I sources, such an evolutionary scenario is unlikely. The difference between groups I and II may reflect different evolutionary pathways of protoplanetary disks.

### More Cosmic Ray Effects on Protoplanetary Disk Formation

Cosmic-ray propagation at small scale: a support for protostellar disc formation

Authors:

Abstract:

As long as magnetic fields remain frozen into the gas, the magnetic braking prevents the formation of protostellar discs. This condition is subordinate to the ionisation fraction characterising the inmost parts of a collapsing cloud. The ionisation level is established by the number and the energy of the cosmic rays able to reach these regions. Adopting the method developed in our previous studies, we computed how cosmic rays are attenuated as a function of column density and magnetic field strength. We applied our formalism to low- and high-mass star formation models obtained by numerical simulations of gravitational collapse that include rotation and turbulence. In general, we found that the decoupling between gas and magnetic fields, condition allowing the collapse to go ahead, occurs only when the cosmic-ray attenuation is taken into account with respect to a calculation in which the cosmic-ray ionisation rate is kept constant. We also found that the extent of the decoupling zone also depends on the dust grain size distribution and is larger if large grains (of radius about 0.1 microns) are formed by compression and coagulation during cloud collapse. The decoupling region disappears for the high-mass case due to magnetic field diffusion that is caused by turbulence and that is not included in the low-mass models. We infer that a simultaneous study of the cosmic-ray propagation during the cloud's collapse may lead to values of the gas resistivity in the innermost few hundred AU around a forming protostar that is higher than generally assumed.

## Friday, April 17, 2015

### Detection of Water Rich Asteroids Accreting Into White Dwarf SDSS J124231.07+522626.6?

Likely detection of water-rich asteroid debris in a metal-polluted white dwarf

Authors:

Abstract:

The cool white dwarf SDSS J124231.07+522626.6 exhibits photospheric absorption lines of 8 distinct heavy elements in medium resolution optical spectra, notably including oxygen. The Teff = 13000 K atmosphere is helium-dominated, but the convection zone contains significant amounts of hydrogen and oxygen. The four most common rock-forming elements (O, Mg, Si, and Fe) account for almost all the accreted mass, totalling at least 1.2e+24 g, similar to the mass of Ceres. The time-averaged accretion rate is 2e+10 g/s, one of the highest rates inferred among all known metal-polluted white dwarfs. We note a large oxygen excess, with respect to the most common metal oxides, suggesting that the white dwarf accreted planetary debris with a water content of ~38 per cent by mass. This star, together with GD 61, GD 16, and GD 362, form a small group of outliers from the known population of evolved planetary systems accreting predominantly dry, rocky debris. This result strengthens the hypothesis that, integrated over the cooling ages of white dwarfs, accretion of water-rich debris from disrupted planetesimals may significantly contribute to the build-up of trace hydrogen observed in a large fraction of helium-dominated white dwarf atmospheres.

### How Much Water Does Brown Dwarf/Giant Planet Kappa Andromedae b Have?

The Water Abundance of the Directly Imaged Substellar Companion κ And b Retrieved from a Near Infrared Spectrum

Authors:

Todorov et al

Abstract:

Recently, spectral retrieval has proven to be a powerful tool for constraining the physical properties and atmospheric compositions of extrasolar planet atmospheres from observed spectra, primarily for transiting objects but also increasingly for directly imaged planets and brown dwarfs. Despite its strengths, this approach has been applied to only about a dozen targets. Determining the abundances of the main carbon and oxygen-bearing compounds in a planetary atmosphere can lead to the C/O ratio of the object, which is crucial in understanding its formation and migration history. We present a retrieval analysis on the published near-infrared spectrum of {\kappa} And b, a directly imaged substellar companion to a young B9 star. We fit the emission spectrum model utilizing a Markov Chain Monte Carlo algorithm. We estimate the abundance of water vapor, and its uncertainty, in the atmosphere of the object. We also place upper limits on the abundances of carbon dioxide and methane and constrain the pressure-temperature profile of the atmosphere. We compare our results to studies that have applied model retrieval on multiband photometry and emission spectroscopy of hot Jupiters (extrasolar giant planets with orbital periods of several days) and the directly imaged giant planet HR 8799b. We find that the water abundances of the hot Jupiters and the two directly imaged planets inhabit overlapping regions of parameter space and that their P-T profiles are qualitatively similar, despite the wide range of effective temperatures and incident stellar fluxes for these objects.

### Brown Dwarf LSR J1835+3259's Magnetic Field

Magnetic field on the brown dwarf LSR J1835+3259

Authors:

Kuzmychov et al

Abstract:

We model the full-Stokes spectrum of the brown dwarf LSR J1835+3259 in the bands of the diatomic molecules CrH, TiO, and FeH in order to infer its magnetic properties. The models are then compared to the observational data obtained with the Low Resolution Imaging Spectrograph (LRISp) at the Keck observatory. Our preliminary analysis shows that the brown dwarf considered possesses a magnetic field of the order of 2-3 kG.

## Thursday, April 16, 2015

### Jupiters Grand Attack and Shaping of our Solar System in Light of Exoplanetary Systems (a seti talk)

One of the problems with his model and its predictions (as he discusses at the end) is that he states close in, tightly packed systems like Gliese 667C or the like, are going to be mutually exclusive of having gas giants in orbits in the outer system.  Yet, we know of several where there are close-in, tightly packed systems with gas giants or giant planets in the outer system, for example, HD 10180, HD 187123 or HD 125612 or the list goes on.  These contradict the predictions  of the Grand Track model based as he lays them out.

Minimally, his model ought to be taking into account these systems.  And should be reworked with the currently known exoplanetary systems in mind.

### WASP-6b Migrated Into Becoming a Inflated Hot Jupiter

Transits and starspots in the WASP-6 planetary system

Authors:

Tregloan-Reed et al

Abstract:

We present updates to \textsc{prism}, a photometric transit-starspot model, and \textsc{gemc}, a hybrid optimisation code combining MCMC and a genetic algorithm. We then present high-precision photometry of four transits in the WASP-6 planetary system, two of which contain a starspot anomaly. All four 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 0.836±0.063M and 0.864±0.024R, respectively. For the planet we find a mass of 0.485±0.027MJup, a radius of 1.230±0.035RJup and a density of 0.244±0.014ρJup. These values are consistent with those found in the literature. In the likely hypothesis that the two spot anomalies are caused by the same starspot or starspot complex, we measure the stars rotation period and velocity to be 23.80±0.15\,d and 1.78±0.20\,km\,s−1, respectively, at a co-latitude of 75.8∘. We find that the sky-projected angle between the stellar spin axis and the planetary orbital axis is λ=7.2∘±3.7∘, indicating axial alignment. Our results are consistent with and more precise than published spectroscopic measurements of the Rossiter-McLaughlin effect. These results suggest that WASP-6b formed at a much greater distance from its host star and suffered orbital decay through tidal interactions with the protoplanetary disc.

### Potassium Detected in hot Jupiter HAT-P-1b's Atmosphere

GTC OSIRIS transiting exoplanet atmospheric survey: detection of potassium in HAT-P-1b from narrowband spectrophotometry

Authors:

Wilson et al

Abstract:

We present the detection of potassium in the atmosphere of HAT-P-1b using optical transit narrowband photometry. The results are obtained using the 10.4 m Gran Telescopio Canarias (GTC) together with the OSIRIS instrument in tunable filter imaging mode. We observed four transits, two at continuum wavelengths outside the potassium feature, at 6792 {\AA} and 8844 {\AA}, and two probing the potassium feature in the line wing at 7582.0 {\AA} and the line core at 7664.9 {\AA} using a 12 {\AA} filter width (R~650). The planet-to-star radius ratios in the continuum are found to be Rpl/R⋆ = 0.1176 ± 0.0013 at 6792 {\AA} and Rpl/R⋆ = 0.1168 ± 0.0022 at 8844 {\AA}, significantly lower than the two observations in the potassium line: Rpl/R⋆ = 0.1248 ± 0.0014 in the line wing at 7582.0 {\AA} and Rpl/R⋆ = 0.1268 ± 0.0012 in the line core at 7664.9 {\AA}. With a weighted mean of the observations outside the potassium feature Rpl/R⋆ = 0.1174 ± 0.0010, the potassium is detected as an increase in the radius ratio of {\Delta}Rpl/R⋆ = 0.0073 ± 0.0017 at 7582.0 {\AA} and {\Delta}Rpl/R⋆ = 0.0094 ± 0.0016 at 7664.9 {\AA} (a significance of 4.3 and 6.1 σ respectively). We hypothesise that the strong detection of potassium is caused by a large scale height, which can be explained by a high-temperature at the base of the upper atmosphere. A lower mean molecular mass caused by the dissociation of molecular hydrogen into atomic hydrogen by the EUV flux from the host star may also partly explain the amplitude of our detection.

### Hot Jupiters Qatar-1b and TrES-5b Revisited

High-precision multi-band time-series photometry of exoplanets Qatar-1b and TrES-5b

Authors:

Mislis et al

Abstract:

We present an analysis of the Qatar-1 and TrES-5 transiting exoplanetary systems, which contain Jupiter-like planets on short-period orbits around K-dwarf stars. Our data comprise a total of 20 transit light curves obtained using five medium-class telescopes, operated using the defocussing technique. The average precision we reach in all our data is RMSQ=1.1 mmag for Qatar-1 (V=12.8) and RMST=1.0 mmag for TrES-5 (V=13.7). We use these data to refine the orbital ephemeris, photometric parameters, and measured physical properties of the two systems. One transit event for each object was observed simultaneously in three passbands (gri) using the BUSCA imager. The QES survey light curve of Qatar-1 has a clear sinusoidal variation on a period of P⋆=23.697±0.123\,d, implying significant starspot activity. We searched for starspot crossing events in our light curves, but did not find clear evidence in any of the new datasets. The planet in the Qatar-1 system did not transit the active latitudes on the surfaces of its host star. Under the assumption that P⋆ corresponds to the rotation period of Qatar-1\,A, the rotational velocity of this star is very close to the vsini⋆ value found from observations of the Rossiter-McLaughlin effect. The low projected orbital obliquity found in this system thus implies a low absolute orbital obliquity, which is also a necessary condition for the transit chord of the planet to avoid active latitudes on the stellar surface.

## Wednesday, April 15, 2015

### Variations Detected in 6 Extreme Debris Disks Hint at Exoplanetary Collisions

Planetary Collisions outside the Solar System: Time Domain Characterization of Extreme Debris Disks

Authors:

Meng et al

Abstract:

Luminous debris disks of warm dust in the terrestrial planet zones around solar-like stars are recently found to vary, indicative of ongoing large-scale collisions of rocky objects. We use Spitzer 3.6 and 4.5 {\mu}m time-series observations in 2012 and 2013 (extended to 2014 in one case) to monitor 5 more debris disks with unusually high fractional luminosities ("extreme debris disk"), including P1121 in the open cluster M47 (80 Myr), HD 15407A in the AB Dor moving group (80 Myr), HD 23514 in the Pleiades (120 Myr), HD 145263 in the Upper Sco Association (10 Myr), and the field star BD+20 307 (>1 Gyr). Together with the published results for ID8 in NGC 2547 (35 Myr), this makes the first systematic time-domain investigation of planetary impacts outside the solar system. Significant variations with timescales shorter than a year are detected in five out of the six extreme debris disks we have monitored. However, different systems show diverse sets of characteristics in the time domain, including long-term decay or growth, disk temperature variations, and possible periodicity.

### Simulating Shocks Driven by Giant Exoplanets in Protoplanetary Disks

On shocks driven by high-mass planets in radiatively inefficient disks. I. Two-dimensional global disk simulations

Authors:

Richert et al

Abstract:

Recent observations of gaps and non-axisymmetric features in the dust distributions of transition disks have been interpreted as evidence of embedded massive protoplanets. However, comparing the predictions of planet-disk interaction models to the observed features has shown far from perfect agreement. This may be due to the strong approximations used for the predictions. For example, spiral arm fitting typically uses results that are based on low-mass planets in an isothermal gas. In this work, we describe two-dimensional, global, hydrodynamical simulations of disks with embedded protoplanets, with and without the assumption of local isothermality, for a range of planet-to-star mass ratios 1-10 M_jup for a 1 M_sun star. We use the Pencil Code in polar coordinates for our models. We find that the inner and outer spiral wakes of massive protoplanets (M>5 M_jup) produce significant shock heating that can trigger buoyant instabilities. These drive sustained turbulence throughout the disk when they occur. The strength of this effect depends strongly on the mass of the planet and the thermal relaxation timescale; for a 10 M_jup planet embedded in a thin, purely adiabatic disk, the spirals, gaps, and vortices typically associated with planet-disk interactions are disrupted. We find that the effect is only weakly dependent on the initial radial temperature profile. The spirals that form in disks heated by the effects we have described may fit the spiral structures observed in transition disks better than the spirals predicted by linear isothermal theory.

### Five Gas Giants Orbiting Metal Rich Stars

Five New Exoplanets Orbiting Three Metal-Rich, Massive Stars: Two-Planet Systems Including Long-Period Planets, and an Eccentric Planet

Authors:

Harakawa et al

Abstract:

We report detections of new exoplanets from a radial velocity (RV) survey of metal-rich FGK stars by using three telescopes. By optimizing our RV analysis method to long time-baseline observations, we have succeeded in detecting five new Jovian-planets around three metal-rich stars HD 1605, HD 1666, and HD 67087 with the masses of 1.3M, 1.5M, and 1.4M, respectively. A K1 subgiant star HD 1605 hosts two planetary companions with the minimum masses of Mpsini=0.96MJUP and 3.5MJUP in circular orbits with the planets' periods P=577.9 days and 2111 days, respectively. HD 1605 shows a significant linear trend in RVs. Such a system consisting of Jovian planets in circular orbits has rarely been found and thus HD 1605 should be an important example of a multi-planetary system that is likely unperturbed by planet-planet interactions. HD 1666 is a F7 main sequence star which hosts an eccentric and massive planet of Mpsini=6.4MJUP in the orbit with ap=0.94 AU and an eccentricity e=0.63. Such an eccentric and massive planet can be explained as a result of planet-planet interactions among Jovian planets. While we have found the large residuals of rms=35.6 m s−1, the periodogram analysis does not support any additional periodicities. Finally, HD 67087 hosts two planets of Mpsini=3.1MJUP and 4.9MJUP in orbits with P=352.2 days and 2374 days, and e=0.17 and 0.76, respectively. Although the current RVs do not lead to accurate determinations of its orbit and mass, HD 67087 c can be one of the most eccentric planets ever discovered in multiple systems.

## Tuesday, April 14, 2015

### Deforming Exoplanets Through Tidal Forces

The flattenings of the layers of rotating planets and satellites deformed by a tidal potential

Authors:

Folonier et al

Abstract:

We consider the Clairaut theory of the equilibrium ellipsoidal figures for differentiated non-homogeneous bodies in non-synchronous rotation adding to it a tidal deformation due to the presence of an external gravitational force. We assume that the body is a fluid formed by n homogeneous layers of ellipsoidal shape and we calculate the external polar flattenings and the mean radius of each layer, or, equivalently, their semiaxes. To first order in the flattenings, the general solution can be written as ϵk=k∗ϵh and μk=k∗μh, where k is a characteristic coefficient for each layer which only depends on the internal structure of the body and ϵh,μh are the flattenings of the equivalent homogeneous problem. For the continuous case, we study the Clairaut differential equation for the flattening profile, using the Radau transformation to find the boundary conditions when the tidal potential is added. Finally, the theory is applied to several examples: i) a body composed of two homogeneous layers; ii) bodies with simple polynomial density distribution laws and iii) bodies following a polytropic pressure-density law.

### Comparing Gyrochronological and Isochronal Age For Transiting Exoplanet Host Stars

A comparison of gyrochronological and isochronal age estimates for transiting exoplanet host stars

Authors:

Maxted et al

Abstract:

Previous studies suggest that tidal interactions may be responsible for discrepancies between the ages of exoplanet host stars estimated using stellar models (isochronal ages) and age estimates based on the stars' rotation periods (gyrochronological ages). We have compiled a sample of 28 transiting exoplanet host stars with measured rotation periods. We use a Bayesian Markov chain Monte Carlo method to determine the joint posterior distribution for the mass and age of each star in the sample, and extend this method to include a calculation of the posterior distribution of the gyrochronological age. The gyrochronological age (τgyro) is significantly less than the isochronal age for about half of the stars in our sample. Tidal interactions between the star and planet are a reasonable explanation for this discrepancy in some cases, but not all. The distribution of τgyro values is evenly spread from very young ages up to a maximum value of a few Gyr. There is no clear correlation between τgyro and the strength of the tidal force on the star due to the innermost planet. There is clear evidence that the isochronal ages for some K-type stars are too large, and this may also be the case for some G-type stars. This may be the result of magnetic inhibition of convection. There is currently no satisfactory explanation for the discrepancy between the young age for CoRoT-2 estimated from either gyrochronology or its high lithium abundance, and the extremely old age for its K-type stellar companion inferred from its very low X-ray flux. There is now strong evidence that the gyrochronological ages of some transiting exoplanet host stars are significantly less than their isochronal ages, but it is not always clear that this is good evidence for tidal interactions between the star and the planet.

### Interesting Populations in Giant Exoplanets Orbiting Giant Stars

Chemical abundances and kinematics of 257 G-, K-type field giants. Setting a base for further analysis of giant-planet properties orbiting evolved stars

Authors:

Abidekyan et al

Abstract:

We performed a uniform and detailed abundance analysis of 12 refractory elements (Na, Mg, Al, Si, Ca, Ti, Cr, Ni, Co, Sc, Mn, and V) for a sample of 257 G- and K-type evolved stars from the CORALIE planet search program. To date, only one of these stars is known to harbor a planetary companion. We aimed to characterize this large sample of evolved stars in terms of chemical abundances and kinematics, thus setting a solid base for further analysis of planetary properties around giant stars. This sample, being homogeneously analyzed, can be used as a comparison sample for other planet-related studies, as well as for different type of studies related to stellar and Galaxy astrophysics. The abundances of the chemical elements were determined using an LTE abundance analysis relative to the Sun, with the spectral synthesis code MOOG and a grid of Kurucz ATLAS9 atmospheres. To separate the Galactic stellar populations both a purely kinematical approach and a chemical method were applied. We confirm the overabundance of Na in giant stars compared to the field FGK dwarfs. This enhancement might have a stellar evolutionary character, but departures from LTE may also produce a similar enhancement. Our chemical separation of stellar populations also suggests a "gap" in metallicity between the thick-disk and high-alpha metal-rich stars, as previously observed in dwarfs sample from HARPS. The present sample, as most of the giant star samples, also suffers from the B - V colour cut-off, which excludes low-log g stars with high metallicities, and high-logg star with low-[Fe/H]. For future studies of planet occurrence dependence on stellar metallicity around these evolved stars we suggest to use a sub-sample of stars in a "cut-rectangle" in the logg - [Fe/H] diagram to overcome the aforementioned issue.