Thursday, December 31, 2015

Hot Jupiter WASP-43b's Orbit is Slowly Decaying

The Possible Orbital Decay and Transit Timing Variations of the Planet WASP-43b

Authors:

Jiang et al

Abstract:

Motivated by the previously reported high orbital decay rate of the planet WASP-43b, eight newly transit light curves are obtained and presented. Together with other data in literature, we perform a self-consistent timing analysis with data covering a timescale of 1849 epochs. The results give an orbital decay rate dP/dt = -0.02890795\pm 0.00772547 sec/year, which is one order smaller than previous values. This slow decay rate corresponds to a normally assumed theoretical value of stellar tidal dissipation factor. In addition, through the frequency analysis, the transit timing variations presented here are unlikely to be periodic, but could be signals of a slow orbital decay.

Do hot Jupiters Inflate Because of Solar Wind/Magnetic Field Interaction Driven Heating?

Extended Heat Deposition in Hot Jupiters: Application to Ohmic Heating

Authors:

Ginzburg et al

Abstract:

Many giant exoplanets in close orbits have observed radii which exceed theoretical predictions. One suggested explanation for this discrepancy is heat deposited deep inside the atmospheres of these "hot Jupiters". Here, we study extended power sources which distribute heat from the photosphere to the deep interior of the planet. Our analytical treatment is a generalization of a previous analysis of localized "point sources". We model the deposition profile as a power law in the optical depth and find that planetary cooling and contraction halt when the internal luminosity (i.e. cooling rate) of the planet drops below the heat deposited in the planet's convective region. A slowdown in the evolutionary cooling prior to equilibrium is possible only for sources which do not extend to the planet's center. We estimate the Ohmic dissipation resulting from the interaction between the atmospheric winds and the planet's magnetic field, and apply our analytical model to Ohmically heated planets. Our model can account for the observed radii of many inflated planets which have equilibrium temperatures ≈1500 K−2500 K, and are inflated to a radius ≈1.5RJ. However, some extremely inflated planets remain unexplained by our model. We also argue that Ohmically inflated planets have already reached their equilibrium phase, and no longer contract. Following Wu & Lithwick (2013) who argued that Ohmic heating could only suspend and not reverse contraction, we calculate the time it takes Ohmic heating to re-inflate a cold planet to its equilibrium configuration. We find that while it is possible to re-inflate a cold planet, the re-inflation timescales are longer by a factor of ≈30 than the cooling time.

Formation and Stellar Spin-Orbit Misalignment of Hot Jupiters from Lidov-Kozai Oscillations in Stellar Binaries

Formation and Stellar Spin-Orbit Misalignment of Hot Jupiters from Lidov-Kozai Oscillations in Stellar Binaries

Authors:

Anderson et al

Abstract:

Observed hot Jupiter (HJ) systems exhibit a wide range of stellar spin-orbit misalignment angles. The origin of these HJs remains unclear. This paper investigates the inward migration of giant planets due to Lidov-Kozai (LK) oscillations induced by a distant (100-1000 AU) stellar companion. We conduct a large population synthesis study, including the octupole gravitational potential from the stellar companion, mutual precession of the host stellar spin axis and planet orbital axis, tidal dissipation in the planet, and stellar spin-down in the host star due to magnetic braking. We consider a range of planet masses (0.3−5MJ) and initial semi-major axes (1−5AU), different properties for the host star, and varying tidal dissipation strengths. The fraction of systems that result in HJs depends on planet mass and stellar type, with fHJ=1−4% (depending on tidal dissipation strength) for Mp=1MJ, and larger (up to 8%) for more massive planets. The production efficiency of "hot Saturns" (Mp=0.3MJ) is much lower, because most migrating planets are tidally disrupted. We find that the fraction of systems that result in either HJ formation or tidal disruption, fmig≃11−14% is roughly constant, having little variation with planet mass, stellar type and tidal dissipation strength. This "universal" migration fraction can be understood qualitatively from analytical migration criteria based on the properties of octupole LK oscillations. The distribution of final HJ stellar obliquities exhibits a complex dependence on the planet mass and stellar type. For Mp=(1−3)MJ, the distribution is always bimodal, with peaks around 30∘ and 130∘. The distribution for 5MJ planets depends on host stellar type, with a preference for low obliquities for solar-type stars, and higher obliquities for more massive (1.4M⊙) stars.

Wednesday, December 30, 2015

Detecting Shocks Waves From High-mass Planets in Protoplanetary Disks

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

Authors:

Lyra et al

Abstract:

Recent high-resolution, near-infrared images of protoplanetary disks have shown that these disks often present spiral features. Spiral arms are among the structures predicted decades ago by numerical simulations of disk-planet interaction and thus it is tempting to suspect that planetary perturbers are responsible for the observed signatures. However, such interpretation is not free of problems. The spirals are found to have large pitch angles, and in at least one case the spiral feature appears effectively unpolarized, which implies thermal emission at roughly 1000 K. We have recently shown in two-dimensional models that shock dissipation in the supersonic wake of high-mass planets can lead to significant heating if the disk is sufficiently adiabatic. In this paper we extend this analysis to three dimensions in thermodynamically evolving disks. We use the Pencil Code in spherical coordinates for our models, with a prescription for thermal cooling based on the optical depth of the local vertical gas column. We use a 5MJ planet, and show that shocks in the region around the planet where the Lindblad resonances occur heat the gas to substantially higher temperatures than the ambient disk gas at that radius. The gas is accelerated vertically away from the midplane by the shocks to form shock bores, and the gas falling back toward the midplane breaks up into a turbulent surf near the Lindblad resonances. This turbulence, although localized, has high α values, reaching 0.05 in the inner Lindblad resonance, and 0.1 in the outer one. We also find evidence that the disk regions heated up by the planetary shocks eventually becomes superadiabatic, generating convection far from the planet's orbit.

HD 100546b is a SuperJovian and HD 100546c is a SuperJovian at 13 AU

Resolving the HD 100546 Protoplanetary System with the Gemini Planet Imager: Evidence for Multiple Forming, Accreting Planets

Authors:

Currie et al

Abstract:

We report Gemini Planet Imager H band high-contrast imaging/integral field spectroscopy and polarimetry of the HD 100546, a 10 Myr-old early-type star recently confirmed to host a thermal infrared bright (super)jovian protoplanet at wide separation, HD 100546 b. We resolve the inner disk cavity in polarized light, recover the thermal-infrared (IR) bright arm, and identify one additional spiral arm. We easily recover HD 100546 b and show that much of its emission originates an unresolved, point source. HD 100546 b likely has extremely red infrared colors compared to field brown dwarfs, qualitatively similar to young cloudy superjovian planets, however, these colors may instead indicate that HD 100546 b is still accreting material from a circumplanetary disk. Additionally, we identify a second point source-like peak at rproj ∼ 13 AU, located just interior to or at inner disk wall consistent with being a 10--20 MJ candidate second protoplanet-- "HD 100546 c" -- and lying within a weakly polarized region of the disk but along an extension of the thermal IR bright spiral arm. Alternatively, it is equally plausible that this feature is a weakly polarized but locally bright region of the inner disk wall. Astrometric monitoring of this feature over the next 2 years and emission line measurements could confirm its status as a protoplanet, rotating disk hot spot that is possibly a signpost of a protoplanet, or a stationary emission source from within the disk.

Inferring Planet Mass from Spiral Structures in Protoplanetary Disks

Inferring Planet Mass from Spiral Structures in Protoplanetary Disks

Authors:

Fung et al

Abstract:

Recent observations of protoplanetary disk have reported spiral structures that are potential signatures of embedded planets, and modeling efforts have shown that a single planet can excite multiple spiral arms, in contrast to conventional disk-planet interaction theory. Using two and three-dimensional hydrodynamics simulations to perform a systematic parameter survey, we confirm the existence of multiple spiral arms in disks with a single planet, and discover a scaling relation between the azimuthal separation of the primary and secondary arm, ϕsep, and the planet-to-star mass ratio q: ϕsep=102∘(q/0.001)0.2 for companions between Neptune mass and 16 Jupiter masses around a 1 solar mass star, and ϕsep=180∘ for brown dwarf mass companions. This relation is independent of the disk's temperature, and can be used to infer a planet's mass to within an accuracy of about 30% given only the morphology of a face-on disk. Combining hydrodynamics and Monte-Carlo radiative transfer calculations, we verify that our numerical measurements of ϕsep are accurate representations of what would be measured in near-infrared scattered light images, such as those expected to be taken by Gemini/GPI, VLT/SPHERE, or Subaru/SCExAO in the future. Finally, we are able to infer, using our scaling relation, that the planet responsible for the spiral structure in SAO 206462 has a mass of about 6 Jupiter masses.

Tuesday, December 29, 2015

Host Star-ExoPlanet Magnetic Interaction

Magnetic games between a planet and its host star: the key role of topology

Authors:

Strugarek et al

Abstract:

Magnetic interactions between a star and a close-in planet are postulated to be a source of enhanced emissions and to play a role in the secular evolution of the orbital system. Close-in planets generally orbit in the sub-alfv\'enic region of the stellar wind, which leads to efficient transfers of energy and angular momentum between the star and the planet. We model the magnetic interactions occurring in close-in star-planet systems with three-dimensional, global, compressible magneto-hydrodynamic numerical simulations of a planet orbiting in a self-consistent stellar wind. We focus on the cases of magnetized planets and explore three representative magnetic configurations. The Poynting flux originating from the magnetic interactions is an energy source for enhanced emissions in star-planet systems. Our results suggest a simple geometrical explanation for ubiquitous on/off enhanced emissions associated with close-in planets, and confirm that the Poynting fluxes can reach powers of the order of 1019 W. Close-in planets are also showed to migrate due to magnetic torques for sufficiently strong stellar wind magnetic fields. The topology of the interaction significantly modifies the shape of the magnetic obstacle that leads to magnetic torques. As a consequence, the torques can vary by at least an order of magnitude as the magnetic topology of the interaction varies.

30 Arietis B Hosts Both Exoplanets & a Star

On the Stellar Companion to the Exoplanet Hosting Star 30 Arietis B

Authors:

Kane et al

Abstract:

A crucial aspect of understanding planet formation is determining the binarity of the host stars. Results from radial velocity surveys and the follow-up of Kepler exoplanet candidates have demonstrated that stellar binarity certainly does not exclude the presence of planets in stable orbits and the configuration may in fact be relatively common. Here we present new results for the 30 Arietis system which confirms that the B component hosts both planetary and stellar companions. Keck AO imaging provides direct detection of the stellar companion and additional radial velocity data are consistent with an orbiting star. We present a revised orbit of the known planet along with photometry during predicted transit times. Finally, we provide constraints on the properties of the stellar companion based on orbital stability considerations.

Exoplanet Signatures and Effect on the Chemical Evolution of Their Host Stars

Planet signatures and effect of the chemical evolution of the Galactic thin-disk stars

Authors:

Spina et al

Abstract:

Context:

Studies based on high-precision abundance determinations revealed that chemical patterns of solar twins are characterised by the correlation between the differential abundances relative to the Sun and the condensation temperatures (Tc) of the elements. It has been suggested that the origin of this relation is related to the chemical evolution of the Galactic disk, but other processes, associated with the presence of planets around stars, might also be involved.

Aims:

We analyse HIRES spectra of 14 solar twins and the Sun to provide new insights on the mechanisms that can determine the relation between [X/H] and Tc.

Methods:

Our spectroscopic analysis produced stellar parameters (Teff, log g, [Fe/H], and ξ), ages, masses, and abundances of 22 elements (C, O, Na, Mg, Al, Si, S, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Y, and Ba). We used these determinations to place new constraints on the chemical evolution of the Galactic disk and to verify whether this process alone can explain the different [X/H]-Tc slopes observed so far.

Results:

We confirm that the [X/Fe] ratios of all the species correlate with age. The slopes of these relations allow us to describe the effect that the chemical evolution of the Galactic disk has on the chemical patterns of the solar twins. After subtracting the chemical evolution effect, we find that the unevolved [X/H]-Tc slope values do not depend on the stellar ages anymore. However, the wide diversity among these [X/H]-Tc slopes, covering a range of ±4~10−5 dex K−1, indicates that processes in addition to the chemical evolution may affect the [X/H]-Tc slopes.

Conclusions:

The wide range of unevolved [X/H]-Tc slope values spanned at all ages by our sample could reflect the wide diversity among exo-planetary systems observed so far and the variety of fates that the matter in circumstellar disks can experience.

Monday, December 28, 2015

James Webb Space Telescope's Mirror is Half Complete

Inside NASA's Goddard Space Flight Center's massive clean room in Greenbelt, Maryland, the ninth flight mirror was installed onto the telescope structure with a robotic arm. This marks the halfway completion point for the James Webb Space Telescope's segmented primary mirror.

The James Webb Space Telescope team has been working tirelessly to install all 18 of Webb's mirror segments onto the telescope structure.

"The years of planning and practicing is really paying dividends and the progress is really rewarding for everyone to see," said NASA's Optical Telescope Element Manager Lee Feinberg.

In these NASA images, the engineering team is seen using a robotic arm to lift and lower the hexagonal-shaped segment that measures just over 4.2 feet (1.3 meters) across and weighs approximately 88 pounds (40 kilograms). After being pieced together, the 18 primary mirror segments will work together as one large 21.3-foot (6.5-meter) mirror. The full installation is expected to be complete early in 2016.

Stability of Earth-mass Planets in the Kepler-68 System

Stability of Earth-mass Planets in the Kepler-68 System

Author:

Kane

Abstract:

A key component of characterizing multi-planet exosystems is testing the orbital stability based on the observed properties. Such characterization not only tests the validity of how observations are interpreted but can also place additional constraints upon the properties of the detected planets. The Kepler mission has identified hundreds of multi-planet systems but there are a few that have additional non-transiting planets and also have well characterized host stars. Kepler-68 is one such system for which we are able to provide a detailed study of the orbital dynamics. We use the stellar parameters to calculate the extent of the Habitable Zone for this system, showing that the outer planet lies within that region. We use N-body integrations to study the orbital stability of the system, in particular placing an orbital inclination constraint on the outer planet of i greater than 5 degrees. Finally, we present the results of an exhaustive stability simulation that investigates possible locations of stable orbits for an Earth-mass planet. We show that there are several islands of stability within the Habitable Zone that could harbor such a planet, most particularly at the 2:3 mean motion resonance with the outer planet.

Quantifying the Origins of Life on a Planetary Scale

Quantifying the Origins of Life on a Planetary Scale

Authors:

Scharf et al

Abstract:

A simple, heuristic formula with parallels to the Drake Equation is introduced to help focus discussion on open questions for the origins of life in a planetary context. This approach indicates a number of areas where quantitative progress can be made on parameter estimation for determining origins of life probabilities. We also suggest that the probability of origin of life events can be dramatically increased on planets with parallel chemistries that can undergo the development of complexity, and in solar systems where more than one planet is available for chemical evolution, and where efficient impact ejecta exchange occurs, increasing the effective chemical search space and available time.

HARPS-N Observes the Sun as a Star

HARPS-N observes the Sun as a star

Authors:

Dumusque et al

Abstract:

Radial velocity perturbations induced by stellar surface inhomogeneities including spots, plages and granules currently limit the detection of Earth-twins using Doppler spectroscopy. Such stellar noise is poorly understood for stars other than the Sun because their surface is unresolved. In particular, the effects of stellar surface inhomogeneities on observed stellar radial velocities are extremely difficult to characterize, and thus developing optimal correction techniques to extract true stellar radial velocities is extremely challenging. In this paper, we present preliminary results of a solar telescope built to feed full-disk sunlight into the HARPS-N spectrograph, which is in turn calibrated with an astro-comb. This setup enables long-term observation of the Sun as a star with state-of-the-art sensitivity to radial velocity changes. Over seven days of observing in 2014, we show an average 50\cms radial velocity rms over a few hours of observation. After correcting observed radial velocities for spot and plage perturbations using full-disk photometry of the Sun, we lower by a factor of two the weekly radial velocity rms to 60\cms. The solar telescope is now entering routine operation, and will observe the Sun every clear day for several hours. We will use these radial velocities combined with data from solar satellites to improve our understanding of stellar noise and develop optimal correction methods. If successful, these new methods should enable the detection of Venus over the next two to three years, thus demonstrating the possibility of detecting Earth-twins around other solar-like stars using the radial velocity technique.

Sunday, December 27, 2015

A Response to Elvis' 2015 Critique of the AURA Report "From Cosmic Birth to Living Earths"

A Response to Elvis' 2015 Critique of the AURA Report "From Cosmic Birth to Living Earths"

Authors:

Seager et al

Abstract:

To ensure progress in astronomy over the coming decades, the key questions are "what facilities will we build, and when?" Toward this end, the Association of Universities for Research in Astronomy (AURA) recently commissioned a study on future space-based options for UV and optical astronomy. The resulting study - "From Cosmic Births to Living Earths" - concluded that a space telescope equipped with a 12-meter class primary mirror would make fundamental advances across virtually all of astrophysics, including finding and characterizing the atmospheres of dozens of Earth-like planets. This ambitious telescope concept is referred to as the High Definition Space Telescope (HDST). In a recent arXiv white paper, Elvis (2015) critiqued a subset of the findings of the AURA study, focusing on the detection and characterization of rocky exoplanets in the habitable zone. In this response, we clarify these issues to confirm that HDST would play a transformative role in the study of terrestrial worlds. Its capabilities for studying exoplanets would be truly unique, even in 2035, and would complement HDST's broad and deep range of exciting astrophysics.

MORSE: Microlensing Observations Rapid Search for Exoplanets

Microlensing Observations Rapid Search for Exoplanets: MORSE code for GPUs

Authors:

McDougall et al

Abstract:

The rapid analysis of ongoing gravitational microlensing events has been integral to the successful detection and characterisation of cool planets orbiting low mass stars in the Galaxy. In this paper we present an implementation of search and fit techniques on Graphical Processing Unit hardware. The method allows for the rapid identification of candidate planetary microlensing events and their subsequent followup for detailed characterisation.

Lightning (!) in Protoplanetary Disks

Development of a Method for the Observation of Lightning in Protoplanetary Disks Using Ion Lines

Authors:

Muranushi et al

Abstract:

In this paper, we propose observational methods for detecting lightning in protoplanetary disks. We do so by calculating the critical electric field strength in the lightning matrix gas (LMG), the parts of the disk where the electric field is strong enough to cause lightning. That electric field accelerates multiple positive ion species to characteristic terminal velocities. In this paper, we present three distinct discharge models, with corresponding critical electric fields. We simulate the position-velocity diagrams and the integrated emission maps for the models. We calculate the measure of sensitivity values for detection of the models, and for distinguishing between the models. At the distance of TW-Hya (54pc), LMG that occupies 2π in azimuth and 25au less than r less than 50au is 1200σ- to 4000σ-detectable. The lower limits of the radii of 5σ-detectable LMG clumps are between 1.6 au and 5.3 au, depending on the models.

Saturday, December 26, 2015

Gravitational Unstable Protoplanetary Disks can Suppress Kozai-Lidov Oscillation

THE KOZAI–LIDOV MECHANISM IN HYDRODYNAMICAL DISKS. III. EFFECTS OF DISK MASS AND SELF-GRAVITY

Authors:

Fu et al

Abstract:

Previously we showed that a substantially misaligned viscous accretion disk with pressure that orbits around one component of a binary system can undergo global damped Kozai–Lidov (KL) oscillations. These oscillations produce periodic exchanges of the disk eccentricity with inclination. The disk KL mechanism is quite robust and operates over a wide range of binary and disk parameters. However, the effects of self-gravity, which are expected to suppress the KL oscillations for sufficiently massive disks, were ignored. Here, we analyze the effects of disk self-gravity by means of hydrodynamic simulations and compare the results with the expectations of analytic theory. The disk mass required for suppression in the simulations is a few percent of the mass of the central star and this roughly agrees with an analytical estimate. The conditions for suppression of the KL oscillations in the simulations are close to requiring that the disk be gravitationally unstable. We discuss some implications of our results for the dynamics of protoplanetary disks and the related planet formation.

Protostar IRAS 4A is Forming a Protoplanetary Disk

High Resolution 8 mm and 1 cm Polarization of IRAS 4A from the VLA Nascent Disk and Multiplicity (VANDAM) Survey

Authors:

Cox et al

Abstract:

Magnetic fields can regulate disk formation, accretion and jet launching. Until recently, it has been difficult to obtain high resolution observations of the magnetic fields of the youngest protostars in the critical region near the protostar. The VANDAM survey is observing all known protostars in the Perseus Molecular Cloud. Here we present the polarization data of IRAS 4A. We find that with ~ 0.2'' (50 AU) resolution at {\lambda} = 8.1 and 10.3 mm, the inferred magnetic field is consistent with a circular morphology, in marked contrast with the hourglass morphology seen on larger scales. This morphology is consistent with frozen-in field lines that were dragged in by rotating material entering the infall region. The field morphology is reminiscent of rotating circumstellar material near the protostar. This is the first polarization detection of a protostar at these wavelengths. We conclude from our observations that the dust emission is optically thin with {\beta} ~ 1.3, suggesting that mm/cm-sized grains have grown and survived in the short lifetime of the protostar.

HD141569A's Protoplanetary Disk is Dissipating

HD141569A: disk dissipation caught in action

Authors:

Péricaud et al

Abstract:

Debris disks are usually thought to be gas-poor, the gas being dissipated by accretion or evaporation during the protoplanetary phase. HD141569A is a 5 Myr old star harboring a famous debris disk, with multiple rings and spiral features. We present here the first PdBI maps of the 12CO(2-1), 13CO(2-1) gas and dust emission at 1.3 mm in this disk. The analysis reveals there is still a large amount of (primordial) gas extending out to 250 au, i. e. inside the rings observed in scattered light. HD141569A is thus a hybrid disk with a huge debris component, where dust has evolved and is produced by collisions, with a large remnant reservoir of gas.

Friday, December 25, 2015

Rotation of Luhman 16AB Brown Dwarfs

Rotation periods and astrometric motions of the Luhman 16AB brown dwarfs by high-resolution lucky-imaging monitoring

Authors:

Mancini et al

Abstract:

Context.
Photometric monitoring of the variability of brown dwarfs can provide useful information about the structure of clouds in their cold atmospheres. The brown-dwarf binary system Luhman 16AB is an interesting target for such a study, as its components stand at the L/T transition and show high levels of variability. Luhman 16AB is also the third closest system to the Solar system, allowing precise astrometric investigations with ground-based facilities.
Aims.
The aim of the work is to estimate the rotation period and study the astrometric motion of both components.
Methods.
We have monitored Luhman 16AB over a period of two years with the lucky-imaging camera mounted on the Danish 1.54m telescope at La Silla, through a special i+z long-pass filter, which allowed us to clearly resolve the two brown dwarfs into single objects. An intense monitoring of the target was also performed over 16 nights, in which we observed a peak-to-peak variability of 0.20 \pm 0.02 mag and 0.34 \pm 0.02 mag for Luhman 16A and 16B, respectively.
Results.
We used the 16-night time-series data to estimate the rotation period of the two components. We found that Luhman 16B rotates with a period of 5.1 \pm 0.1 hr, in very good agreement with previous measurements. For Luhman 16A, we report that it rotates slower than its companion and, even though we were not able to get a robust determination, our data indicate a rotation period of roughly 8 hr. This implies that the rotation axes of the two components are well aligned and suggests a scenario in which the two objects underwent the same accretion process. The 2-year complete dataset was used to study the astrometric motion of Luhman 16AB. We predict a motion of the system that is not consistent with a previous estimate based on two months of monitoring, but cannot confirm or refute the presence of additional planetary-mass bodies in the system.

2MASS J11193254-1137466: First L7 Brown Dwarf Found in TW Hydrae Association

A Targeted Search for Peculiarly Red L and T Dwarfs in SDSS, 2MASS, and WISE: Discovery of a Possible L7 Member of the TW Hydrae Association

Authors:

Kellogg et al

Abstract:

We present first results from a targeted search for brown dwarfs with unusual red colors indicative of peculiar atmospheric characteristics. These include objects with low surface gravities or with unusual dust content or cloud properties. From a positional cross-match of SDSS, 2MASS and WISE, we have identified 40 candidate peculiar early L to early T dwarfs that are either new objects or have not been identified as peculiar through prior spectroscopy. Using low resolution spectra, we confirm that 10 of the candidates are either peculiar or potential L/T binaries. With a J-Ks color of 2.62 +/- 0.15 mag, one of the new objects --- the L7 dwarf 2MASS J11193254-1137466 --- is among the reddest field dwarfs currently known. Its proper motion and photometric parallax indicate that it is a possible member of the TW Hydrae moving group. If confirmed, it would its lowest-mass (5--6 MJup) free-floating member. We also report a new T dwarf, 2MASS J22153705+2110554, that was previously overlooked in the SDSS footprint. These new discoveries demonstrate that despite the considerable scrutiny already devoted to the SDSS and 2MASS surveys, our exploration of these data sets is not yet complete.

WISE J231921.92+764544.4: a Newly Found L Class Brown Dwarf in Argus

Discovery of an L4β Candidate Member of Argus in the Planetary Mass Regime: WISE J231921.92+764544.4

Authors:

Castro et el

Abstract:

We present the discovery of a young L dwarf, WISE J231921.92+764544.4, identified by comparing the Wide-field Infrared Survey Explorer (WISE) All-Sky Catalog to the Two Micron All Sky Survey (2MASS). A medium-resolution optical spectrum provides a spectral type of L4β, with a photometric distance estimate of 26.1±4.4 pc. The red WISE W1−W2 color provides additional evidence of youth, while the 2MASS J−Ks color does not. WISE J231921.92+764544.4 is a candidate member of the young moving group Argus, with the space motion and position of WISE J231921.92+764544.4 giving a probability of 79% membership in Argus and a probability of 21% as a field object, based on BANYAN II. WISE J231921.92+764544.4 has a mass of 12.1±0.4 MJup based on membership in Argus, within the planetary mass regime.

Combining Photometry From Kepler and TESS to Improve Short-Period Exoplanet Characterization

Combining Photometry From Kepler and TESS to Improve Short-Period Exoplanet Characterization

Authors:

Placek et al

Abstract:

Planets emit thermal radiation and reflect incident light that they recieve from their host stars. As a planet orbits it's host star the photometric variations associated with these two effects produce very similar phase curves. If observed through only a single bandpass this leads to a degeneracy between certain planetary parameters that hinder the precise characterization of such planets. However, observing the same planet through two different bandpasses gives one much more information about the planet. Here, we develop a Bayesian methodology for combining photometry from both \emph{Kepler} and the Transiting Exoplanet Survey Satellite (TESS). In addition, we demonstrate via simulations that one can disentangle the reflected and thermally emitted light from the atmosphere of a hot-Jupiter as well as more precisely constrain both the geometric albedo and dayside temperature of the planet. This methodology can further be employed using various combinations of photometry from the James Webb Space Telescope (JWST), the Characterizing ExOplanet Satellite (CHEOPS), or the PLATO mission.

Thursday, December 24, 2015

The Exotic Mantle Materials Hypothesized for SuperEarths

Using mathematical models, scientists have 'looked' into the interior of super-Earths and discovered that they may contain compounds that are forbidden by the classical rules of chemistry -- these substances may increase the heat transfer rate and strengthen the magnetic field on these planets. The findings have been presented in a paper published in the journal Scientific Reports.

The authors of the paper are a group of researchers from MIPT led by Artem Oganov, a professor of the Skolkovo Institute of Science and Technology and the head of the MIPT Laboratory of Computer Design. In a previous study, Oganov and his colleagues used an algorithm created by Oganov called USPEX to identify new compounds of sodium and chlorine, as well as other exotic substances.

In their latest paper, the researchers attempted to find out which compounds may be formed by silicon, oxygen, and magnesium at high pressures. These particular elements were not chosen by chance.

"Earth-like planets consist of a thin silicate crust, a silicate-oxide mantle -- which makes up approximately 7/8 of the Earth's volume and consists more than 90% of silicates and magnesium oxide -- and an iron core. We can say that magnesium, oxygen, and silicon form the basis of chemistry on Earth and on Earth-like planets," says Oganov.

Using the USPEX algorithm, the researchers investigated various structural compositions of Mg-Si-O that may occur at pressures ranging from 5 to 30 million atmospheres. Such pressures may exist in the interior of super-Earths -- planets with a solid surface mass several times greater than the mass of the Earth. There are no planets like this in the solar system, but astronomers know of planets orbiting other stars that are not as heavy as the gas giants, but are considerably heavier than the Earth. They are called super-Earths. These planets include the recently discovered Gliese 832c, which is five times heavier than the Earth, or the mega-Earth Kepler-10c, which is 17 times heavier than the Earth.

The results of the computer modelling show that the interior of these planets may contain the "exotic" compounds MgSi3O12 and MgSiO6. They have many more oxygen atoms than the MgSiO3 on Earth.

In addition, MgSi3O12 is a metal oxide and a conductor, whereas other substances consisting of Mg-Si-O atoms are dielectrics or semiconductors. "Their properties are very different to normal compounds of magnesium, oxygen, and silicon - many of them are metals or semiconductors. This is important for generating magnetic fields on these planets. As magnetic fields produce electrical currents in the interiors of a planet, high conductivity could mean a significantly more powerful magnetic field," explains Oganov.

A more powerful magnetic field means more powerful protection from cosmic radiation, and consequently more favourable conditions for living organisms. The researchers also predicted new magnesium and silicon oxides that do not fit in with the rules of classical chemistry -- SiO, SiO3, and MgO3, in addition to the oxides MgO2 and Mg3O2 previously predicted by Oganov at lower pressures.

EPIC 204129699b: a new hot Jupiter in a 1.26 day orbit

EPIC 204129699b, a grazing transiting hot Jupiter on an 1.26-day orbit around a bright solar like star

Authors:

Grziwa et al

Abstract:

We report the discovery of EPIC 204129699b, the first confirmed transiting hot Jupiter detected by the K2 space mission. We combined K2 photometry with FastCam lucky imaging and FIES and HARPS high-resolution spectroscopy to confirm the planetary nature of the transiting object and derived the system parameters. EPIC 204129699b is a 1.8-Jupiter-mass planet on an 1.26-day-orbit around a G7V star (M* = 0.91 Msun, R* = 0.78 Rsun). The planetary radius is poorly constrained (0.7 less than Rp less than 1.4 RJup ), owing to the grazing transit and the low sampling rate of the K2 photometry. The short orbital period and the brightness of the host star (V = 10.8 mag) make the system amenable to atmospheric characterization.

Effects on Inflated Hot Jupiters Like HD 209458b's Magnetic Field

ATMOSPHERE EXPANSION AND MASS LOSS OF CLOSE-ORBIT GIANT EXOPLANETS HEATED BY STELLAR XUV. II. EFFECTS OF PLANETARY MAGNETIC FIELD; STRUCTURING OF INNER MAGNETOSPHERE

Authors:

Khodachenko et al

Abstract:

This is the second paper in a series where we build a self-consistent model to simulate the mass-loss process of a close-orbit magnetized giant exoplanet, so-called hot Jupiter (HJ). In this paper we generalize the hydrodynamic (HD) model of an HJ's expanding hydrogen atmosphere, proposed in the first paper, to include the effects of intrinsic planetary magnetic field. The proposed self-consistent axisymmetric 2D magnetohydrodynamics model incorporates radiative heating and ionization of the atmospheric gas, basic hydrogen chemistry for the appropriate account of major species composing HJ's upper atmosphere and related radiative energy deposition, and ${{\rm{H}}}_{3}^{+}$ and Lyα cooling processes. The model also takes into account a realistic solar-type X-ray/EUV spectrum for calculation of intensity and column density distribution of the radiative energy input, as well as gravitational and rotational forces acting in a tidally locked planet–star system. An interaction between the expanding atmospheric plasma and an intrinsic planetary magnetic dipole field leads to the formation of a current-carrying magnetodisk that plays an important role for topology and scaling of the planetary magnetosphere. A cyclic character of the magnetodisk behavior, composed of consequent phases of the disk formation followed by the magnetic reconnection with the ejection of a ring-type plasmoid, has been discovered and investigated. We found that the mass-loss rate of an HD 209458b analog planet is weakly affected by the equatorial surface field less than 0.3 G, but is suppressed by an order of magnitude at the field of 1 G.

HATS-14b: a hot Jupiter in an Oblique Orbit Around a G Dwarf

A high obliquity orbit for the hot-Jupiter HATS-14b transiting a 5400K star

Authors:

Zhou et al

Abstract:

We report a spin-orbit misalignment for the hot-Jupiter HATS-14b, measuring a projected orbital obliquity of |lambda|= 76 -5/+4 deg. HATS-14b orbits a high metallicity, 5400 K G dwarf in a relatively short period orbit of 2.8 days. This obliquity was measured via the Rossiter-McLaughlin effect, obtained with observations from Keck-HIRES. The velocities were extracted using a novel technique, optimised for low signal-to-noise spectra, achieving a high precision of 4 m/s point-to-point scatter. However, we caution that our uncertainties may be underestimated. Due to the low rotational velocity of the star, the detection significance is dependent on the vsini prior that is imposed in our modelling. Based on trends observed in the sample of hot Jupiters with obliquity measurements, it has been suggested that these planets modify the spin axes of their host stars, with an efficiency that depends on the stellar type and orbital period of the system. In this framework, short-period planets around stars with surface convective envelopes, like HATS-14b, are expected to have orbits that are aligned with the spin axes of their host stars. HATS-14b, however, is a significant outlier from this trend, challenging the effectiveness of the tidal realignment mechanism.

Wednesday, December 23, 2015

How to map an Exoplanets Rings

In “Astronomers Make a Map of a Super Saturn's Rings,” from the January issue of Scientific American, the Leiden University astronomer Matthew Kenworthy tells the story of discovering a ring system some 200 times larger than Saturn’s around the distant star J1407. Despite its rather large size, across interstellar distances this ring system would normally be totally invisible to us—and in fact Kenworthy and his peers have yet to glimpse J1407b, the giant planet that must be its host. The only reason we know the ring system exists at all is that, by chance, Kenworthy and other researchers happened to see its shadow after it “transited” across the face of its star in 2007.

There's a video on the other end.

Searching for Rings Around Exoplanets

A Search for Ringed Exoplanets using Kepler Photometry

Authors:

Heising et al

Abstract:

Models are developed to simulate lightcurves of stars dimmed by transiting exoplanets with and without rings. These models are then applied to Kepler photometry to search for planetary rings in a sample of 21 exoplanets, mostly hot Jupiters, chosen to offer the best observational opportunity for discovering potential rings. We also examine what kinds of rings might be expected for these planets, in terms of both size and orientation, based on arguments involving the host planet's equilibrium temperature, its likely obliquities, and the formation and stability of possible ring systems. Finding no evidence for rings, for each of the 21 studied planets it is determined on an observational basis which potential rings can be rejected out of a representative set of fiducial rings, varying in both size and orientation. For 12 of the 21 planets, we determined that Saturn-like rings could be ruled out for at least certain orientations. Additionally, the detectability of rings is studied, and it is found that ringed planets with small obliquities (roughly 5∘−10∘) can yield large signals, which is encouraging for future work, since such small obliquities are expected for hot Jupiters.

Re-inflated Warm Jupiters Around Red Giants

Re-inflated Warm Jupiters Around Red Giants

Authors:

Lopez et al

Abstract:

A Correlation Between Host Star Iron Content and Giant Planet Characteristics

SOPHIE velocimetry of Kepler transit candidates XVII. The physical properties of giant exoplanets within 400 days of period

Authors:

Santerne et al

Abstract:

While giant extrasolar planets have been studied for more than two decades now, there are still some open questions such as their dominant formation and migration process, as well as their atmospheric evolution in different stellar environments. In this paper, we study a sample of giant transiting exoplanets detected by the Kepler telescope with orbital periods up to 400 days. We first defined a sample of 129 giant-planet candidates that we followed up with the SOPHIE spectrograph (OHP, France) in a 6-year radial velocity campaign. This allow us to unveil the nature of these candidates and to measure a false-positive rate of 54.6 +/- 6.5 % for giant-planet candidates orbiting within 400 days of period. Based on a sample of confirmed or likely planets, we then derive the occurrence rates of giant planets in different ranges of orbital periods. The overall occurrence rate of giant planets within 400 days is 4.6 +/- 0.6 %. We recover, for the first time in the Kepler data, the different populations of giant planets reported by radial velocity surveys. Comparing these rates with other yields, we find that the occurrence rate of giant planets is lower only for hot jupiters but not for the longer period planets. We also derive a first measurement on the occurrence rate of brown dwarfs in the brown-dwarf desert with a value of 0.29 +/- 0.17 %. Finally, we discuss the physical properties of the giant planets in our sample. We confirm that giant planets receiving a moderate irradiation are not inflated but we find that they are in average smaller than predicted by formation and evolution models. In this regime of low-irradiated giant planets, we find a possible correlation between their bulk density and the Iron abundance of the host star, which needs more detections to be confirmed.

Tuesday, December 22, 2015

Oscillations of Relative Inclination Angles in Compact Extrasolar Planetary Systems

Oscillations of Relative Inclination Angles in Compact Extrasolar Planetary Systems

Authors:

Becker et al

Abstract:

The Kepler Mission has detected dozens of compact planetary systems with more than four transiting planets. This sample provides a collection of close-packed planetary systems with relatively little spread in the inclination angles of the inferred orbits. A large fraction of the observational sample contains limited multiplicity, begging the question whether there is a true diversity of multi transiting systems, or if some systems merely possess high mutual inclinations, allowing them to appear as single-transiting systems in a transit-based survey. This paper begins an exploration of the effectiveness of dynamical mechanisms in exciting orbital inclination within exoplanetary systems of this class. For these tightly packed systems, we determine that the orbital inclination angles are not spread out appreciably through self-excitation. In contrast, the two Kepler multi-planet systems with additional non-transiting planets are susceptible to oscillations of their inclination angles, which means their currently observed configurations could be due to planet-planet interactions alone. We also provide constraints and predictions for the expected transit duration variations (TDVs) for each planet. In these multi-planet compact Kepler systems, oscillations of their inclination angles are remarkably hard to excite; as a result, they tend to remain continually mutually transiting (CMT-stable). We study this issue further by augmenting the planet masses and determining the enhancement factor required for oscillations to move the systems out of transit. The oscillations of inclination found here inform the recently suggested dichotomy in the sample of solar systems observed by Kepler.

Period Ratio Distribution of Near-Resonant Planets Indicate Planetesimal Scattering

Period Ratio Distribution of Near-Resonant Planets Indicate Planetesimal Scattering

Authors:

Chatterjee et al

Abstract:

An intriguing trend among Kepler's multi-planet systems is an overabundance of planet pairs with period ratios just wide of mean motion resonances (MMR) and a dearth of systems just narrow of them. In a recently published paper Chatterjee & Ford (2015; henceforth CF15) has proposed that gas-disk migration traps planets in a MMR. After gas dispersal, orbits of these trapped planets are altered through interaction with a residual planetesimal disk. They found that for massive enough disks planet-planetesimal disk interactions can break resonances and naturally create moderate to large positive offsets from the initial period ratio for large ranges of planetesimal disk and planet properties. Divergence from resonance only happens if the mass of planetesimals that interact with the planets is at least a few percent of the total planet mass. This threshold, above which resonances are broken and the offset from resonances can grow, naturally explains why the asymmetric large offsets were not seen in more massive planet pairs found via past radial velocity surveys. In this article we will highlight some of the key findings of CF15. In addition, we report preliminary results from an extension of this study, that investigates the effects of planet-planetesimal disk interactions on initially non-resonant planet pairs. We find that planetesimal scattering typically increases period ratios of non-resonant planets. If the initial period ratios are below and in proximity of a resonance, under certain conditions, this increment in period ratios can create a deficit of systems with period ratios just below the exact integer corresponding to the MMR and an excess just above. From an initially uniform distribution of period ratios just below a 2:1 MMR, planetesimal interactions can create an asymmetric distribution across this MMR similar to what is observed for the Kepler planet pairs.

An Effective Field Theory Approach to Tidal Dynamics of Astrophysical Systems

An effective field theory approach to tidal dynamics of astrophysical systems

Authors:

Endlich et al

Abstract:

We develop a description of tidal effects in astrophysical systems using effective field theory techniques. Our symmetry-based approach is systematic and equally capable to describe objects in the Newtonian regime (e.g. moons, rocky planets, main sequence stars, etc.) as well as relativistic objects (e.g. neutron stars and black holes). In the Newtonian limit, we recover the dynamical equations for the "weak friction model" with additional corrections due to tidal and rotational deformations.

Monday, December 21, 2015

How Common are Small Exoplanets Around Kepler Stars?

Detailed Abundances of Stars with Small Planets Discovered by Kepler I: The First Sample

Authors:

Schuler et al

Abstract:

We present newly derived stellar parameters and the detailed abundances of 19 elements of seven stars with small planets discovered by NASA's Kepler Mission. Each star save one has at least one planet with a radius less than or equal to 1.6 R_Earth, suggesting a primarily rocky composition. The stellar parameters and abundances are derived from high signal-to-noise ratio, high-resolution echelle spectroscopy obtained with the 10-m Keck I telescope and HIRES spectrometer using standard spectroscopic techniques. The metallicities of the seven stars range from -0.32 dex to +0.13 dex, with an average metallicity that is subsolar, supporting previous suggestions that, unlike Jupiter-type giant planets, small planets do not form preferentially around metal-rich stars. The abundances of elements other than iron are in line with a population of Galactic disk stars, and despite our modest sample size, we find hints that the compositions of stars with small planets are similar to stars without known planets and with Neptune-size planets, but not to those of stars with giant planets. This suggests that the formation of small planets does not require exceptional host-star compositions and that small planets may be ubiquitous in the Galaxy. We compare our derived abundances (which have typical uncertainties of less than or equal 0.04 dex) to the condensation temperature of the elements; a correlation between the two has been suggested as a possible signature of rocky planet formation. None of the stars demonstrate the putative rocky planet signature, despite at least three of the stars having rocky planets estimated to contain enough refractory material to produce the signature, if real. More detailed abundance analyses of stars known to host small planets are needed to verify our results and place ever more stringent constraints on planet formation models.

The UltraViolet Light Environment is VERY Important for Prebiotic Chemistry

Influence of the UV Environment on the Synthesis of Prebiotic Molecules

Authors:

Ranjan et al

Abstract:

Ultraviolet (UV) radiation is common to most planetary environments, and could play a key role in the chemistry of molecules relevant to abiogenesis (prebiotic chemistry). In this work, we explore the impact of UV light on prebiotic chemistry that might occur in liquid water on the surface of a planet with an atmosphere. We consider effects including atmospheric absorption, attenuation by water, and stellar variability to constrain the UV input as a function of wavelength. We conclude that the UV environment would be characterized by broadband input, and wavelengths below 204 nm and 168 nm would be shielded out by atmospheric CO2 and water, respectively. We compare this broadband prebiotic UV input to the narrowband UV sources (e.g. mercury lamps) often used in laboratory studies of prebiotic chemistry, and explore the implications for the conclusions drawn from these experiments. We consider as case studies the ribonucleotide synthesis pathway of Powner et al (2009) and the sugar synthesis pathway of Ritson et al (2012). Irradiation by narrowband UV light from a mercury lamp formed an integral component of these studies: we quantitatively explore the impact of more realistic UV input on the conclusions that can be drawn from these experiments. Finally, we explore the constraints solar UV input places on the buildup of prebiotically important feedstock gasses like CH4 and HCN. Our results demonstrate the importance of characterizing the wavelength dependence (action spectra) of prebiotic synthesis pathways to determine how pathways derived under laboratory irradiation conditions will function under planetary prebiotic conditions.

Understanding the Formation of SuperEarths/Mini Neptunes

Breeding Super-Earths and Birthing Super-Puffs in Transitional Disks

Authors:

Lee et al

Abstract:

The riddle posed by super-Earths (1-4R⊕, 2-20M⊕) is that they are not Jupiters: their core masses are large enough to trigger runaway gas accretion, yet somehow super-Earths accreted atmospheres that weigh only a few percent of their total mass. We show that this puzzle is solved if super-Earths formed late, as the last vestiges of their parent gas disks were about to clear. This scenario would seem to present fine-tuning problems, but we show that there are none. Ambient gas densities can span many (up to 9) orders of magnitude, and super-Earths can still robustly emerge after ∼0.1-1 Myr with percent-by-weight atmospheres. Super-Earth cores are naturally bred in gas-poor environments where gas dynamical friction has weakened sufficiently to allow constituent protocores to merge. So little gas is present at the time of core assembly that cores hardly migrate by disk torques: formation of super-Earths can be in situ. The picture --- that close-in super-Earths form in a gas-poor (but not gas-empty) inner disk, fed continuously by gas that bleeds inward from a more massive outer disk --- recalls the largely evacuated but still accreting inner cavities of transitional protoplanetary disks. We also address the inverse problem presented by super-puffs: an uncommon class of short-period planets seemingly too voluminous for their small masses (4-10R⊕, 2-6M⊕). Super-puffs easily acquire their thick atmospheres as dust-free, rapidly cooling worlds outside ∼1 AU where nebular gas is colder, less dense, and therefore less opaque. Unlike super-Earths which can form in situ, super-puffs migrated in to their current orbits; they are expected to form the outer links of mean-motion resonant chains, and to exhibit greater water content. We close our series on nebular accretion of atmospheres by confronting observations and itemizing remaining questions.

Sunday, December 20, 2015

Do Cooler Protoplanetary Disks NOT Form Gas Giants?

The Role of the Cooling Prescription for Disk Fragmentation: Numerical Convergence & Critical Cooling Parameter in Self-Gravitating Disks

Authors:

Baehr et al

Abstract:

Protoplanetary disks fragment due to gravitational instability when there is enough mass for self-gravitation, described by the Toomre parameter, and when heat can be lost at a rate comparable to the local dynamical timescale, described by t_c=beta Omega^-1. Simulations of self-gravitating disks show that the cooling parameter has a rough critical value at beta_crit=3. When below beta_crit, gas overdensities will contract under their own gravity and fragment into bound objects while otherwise maintaining a steady state of gravitoturbulence. However, previous studies of the critical cooling parameter have found dependence on simulation resolution, indicating that the simulation of self-gravitating protoplanetary disks is not so straightforward. In particular, the simplicity of the cooling timescale t_c prevents fragments from being disrupted by pressure support as temperatures rise. We alter the cooling law so that the cooling timescale is dependent on local surface density fluctuations, a means of incorporating optical depth effects into the local cooling of an object. For lower resolution simulations, this results in a lower critical cooling parameter and a disk more stable to gravitational stresses suggesting the formation of large gas giants planets in large, cool disks is generally suppressed by more realistic cooling. At our highest resolution however, the model becomes unstable to fragmentation for cooling timescales up to beta = 10.

A New Concept for Spectro-photometry of Exoplanets with Space-based Telescopes

A New Concept for Spectro-photometry of Exoplanets with Space-based Telescopes

Authors:

Matsuo et al

Abstract:

We propose a new concept for spectral characterization of transiting exoplanets with future space-based telescopes. This concept, called as densified pupil spectroscopy, allows us to perform high, stable spectrophotometry against telescope pointing jitter and deformation of the primary mirror instead of not having imaging capability. This densified pupil spectrometer comprises the following three roles: division of a pupil into a number of sub-pupils, densification of each sub-pupil, and acquisition of the spectrum of each sub-pupil with a conventional spectrometer. Focusing on the fact that the divided and densified sub-pupil can be treated as a point source, we discovered that a simplified spectrometer allows us to acquire the spectra of the densified sub-pupils on the detector plane-an optical conjugate with the primary mirror-by putting the divided and densified sub-pupils on the entrance slit of the spectrometer. The acquired multiple spectra are not principally moved on the detector against the pointing jitter and the reliability of the observation result is also increased by statistically treating them. Our numerical calculations show that this method potentially suppresses the instrumental systematic error caused by the telescope pointing jitter down to the same level of photon noise as one-hour integration on a cryogenic telescope with a diameter of 2.5m at 10um. Because future cryogenic large telescopes such as the Space Infrared Telescope for Cosmology and Astrophysics (SPICA) and the Cryogenic Aperture Large Infrared Space Observatory (CALISTO) will provide us with a thermally stable environment and a low background, they potentially present the first opportunity to characterize the thermal emissions from terrestrial planets.

Young "Dipper" Stars in Upper Sco and ρ Oph Observed by K2

Young "Dipper" Stars in Upper Sco and ρ Oph Observed by K2

Authors:

Andsell et al

Abstract:

We present ten young (≲10 Myr) late-K and M dwarf stars observed in K2 Campaign 2 that host protoplanetary disks and exhibit quasi-periodic or aperiodic dimming events. Their optical light curves show ∼10-20 dips in flux over the 80-day observing campaign with durations of ∼0.5-2 days and depths of up to ∼40%. These stars are all members of the ρ Ophiuchus (∼1 Myr) or Upper Scorpius (∼10 Myr) star-forming regions. To investigate the nature of these "dippers" we obtained: optical and near-infrared spectra to determine stellar properties and identify accretion signatures; adaptive optics imaging to search for close companions that could cause optical variations and/or influence disk evolution; and millimeter-wavelength observations to constrain disk dust and gas masses. The spectra reveal Li I absorption and Hα emission consistent with stellar youth (less than 50 Myr), but also accretion rates spanning those of classical and weak-line T Tauri stars. Infrared excesses are consistent with protoplanetary disks extending to within ∼10 stellar radii in most cases; however, the sub-mm observations imply disk masses that are an order of magnitude below those of typical protoplanetary disks. We find a positive correlation between dip depth and WISE-2 excess, which we interpret as evidence that the dipper phenomenon is related to occulting structures in the inner disk, although this is difficult to reconcile with the weakly accreting aperiodic dippers. We consider three mechanisms to explain the dipper phenomenon: inner disk warps near the co-rotation radius related to accretion; vortices at the inner disk edge produced by the Rossby Wave Instability; and clumps of circumstellar material related to planetesimal formation.

Saturday, December 19, 2015

Characteristics of Kepler Stars WITHOUT Exoplanets

Rotation periods and seismic ages of KOIs - comparison with stars without detected planets from Kepler observations

Authors:

Ceillier et al

Abstract:

One of the most difficult properties to derive for stars is their age. For cool main-sequence stars, gyrochronology relations can be used to infer stellar ages from measured rotation pe- riods and HR Diagram positions. These relations have few calibrators with known ages for old, long rotation period stars. There is a significant sample of old Kepler objects of inter- est, or KOIs, which have both measurable surface rotation periods and precise asteroseismic measurements from which ages can be accurately derived. In this work we determine the age and the rotation period of solar-like pulsating KOIs to both compare the rotation properties of stars with and without known planets and enlarge the gyrochronology calibration sample for old stars. We use Kepler photometric light curves to derive the stellar surface rotation peri- ods while ages are obtained with asteroseismology using the Asteroseismic Modeling Portal in which individual mode frequencies are combined with high-resolution spectroscopic pa- rameters. We thus determine surface rotation periods and ages for 11 planet-hosting stars, all over 2 Gyr old. We find that the planet-hosting stars exhibit a rotational behaviour that is consistent with the latest age-rotation models and similar to the rotational behaviour of stars without detected planets. We conclude that these old KOIs can be used to test and calibrate gyrochronology along with stars not known to host planets.

Observations of Debris Disks Around Solar-Type Stars

Resolved Millimeter-Wavelength Observations of Debris Disks around Solar-Type Stars

Authors:

Steele et al

Abstract:

The presence of debris disks around young main sequence stars hints at the existence and structure of planetary systems. Millimeter-wavelength observations probe large grains that trace the location of planetesimal belts. The FEPS (Formation and Evolution of Planetary Systems) Spitzer Legacy survey of nearby young solar analogues yielded a sample of five debris disk-hosting stars with millimeter flux suitable for interferometric follow-up. We present observations with the Submillimeter Array (SMA) and the Combined Array for Research in Millimeter-wave Astronomy (CARMA) at ~2" resolution that spatially resolve the debris disks around these nearby (d∼50 pc) stars. Two of the five disks (HD 377, HD 8907) are spatially resolved for the first time and one (HD 104860) is resolved at millimeter wavelengths for the first time. We combine our new observations with archival SMA and Atacama Large Millimeter/Submillimeter Array (ALMA) data to enable a uniform analysis of the full five-object sample. We simultaneously model the broad-band photometric data and resolved millimeter visibilities to constrain the dust temperatures and disk morphologies, and perform an MCMC analysis to fit for basic structural parameters. We find that the radii and widths of the cold outer belts exhibit properties consistent with scaled-up versions of the Solar System's Kuiper Belt. All the disks exhibit characteristic grain sizes comparable to the blowout size, and all the resolved observations of emission from large dust grains are consistent with an axisymmetric dust distribution to within the uncertainties. These results are consistent with comparable studies carried out at infrared wavelengths.

The Effects of Binary AG Tri's Debris Disk

The visual binary AG Tri in β Pictoris Association: can a debris disc cause very different rotation periods of its components?

Authors:

Messina et al

Abstract:

We measure the photometric rotation periods of the components of multiple systems in young stellar associations to investigate the causes of the observed rotation period dispersion. We present the case of the wide binary AG Tri in the 23-Myr young beta Pictoris Association consisting of K4 + M1 dwarfs. Our multi-band, multi-season photometric monitoring allowed us to measure the rotation periods of both components P_A = 12.4d and P_B = 4.66d, to detect a prominent magnetic activity in the photosphere, likely responsible for the measured radial velocity variations, and for the first time, a flare event on the M1 component AG Tri B. We investigate either the possibility that the faster rotating component may have suffered an enhanced primordial disc dispersal, starting its PMS spin-up earlier than the slower rotating component, or the possibility that the formation of a debris disc may have prevented AG Tri A from gaining part of the angular momentum from the accreting disc.

Friday, December 18, 2015

Did Lithium Rich Giant Star KIC 9821622 eat its Exoplanets?

KIC 9821622: An interesting lithium-rich giant in the Kepler field

Authors:

Jofré et al

Abstract:

We report the discovery of a new exceptional young lithium-rich giant, KIC 9821622, in the Kepler field exhibiting unusually large enhancement of α, Fe-peak and \textit{r}-process elements. From high-resolution spectra obtained with GRACES at Gemini North, we derived fundamental parameters and detailed chemical abundances of 23 elements from both equivalent widths and synthesis analysis. Combining atmospheric stellar parameters with available asteroseismic data we obtained the stellar mass, radius and age. The data analysis reveals that KIC 9821622 is a Li-rich (A(Li)NLTE = 1.80 ± 0.2) intermediate-mass giant star (M = 1.64 M⊙) located at the RGB near the luminosity bump. We find unexpected elevated abundances of Fe-peak and \textit{r}-process elements. Also, as previously reported, we find that this is a young star (2.37 Gyr) with unusual high abundances of α-elements ([α/Fe] = 0.31). The evolutionary status of KIC 9821622 suggests that its Li-rich nature is result of internal freshly Li synthesized through the Cameron-Fowler mechanism near the luminosity bump. However, its peculiar enhancement of α, Fe-peak and \textit{r}-process elements opens the possibility of external contamination by material enriched by a supernova explosion. Although less likely, planet accretion cannot be ruled out.

The Formation of a Circumstellar Disk From two White Dwarf Stars Merging to Become a Neutron Star

On the evolution of a fossil disk around neutron stars originating from merging white dwarfs

Authors:

Liu et al

Abstract:

Numerical simulations suggest that merging double white dwarfs (WDs) may produce a newborn neutron star surrounded by a fossil disk. We investigate the evolution of the fossil disk following the coalescence of double WDs. We demonstrate that the evolution can be mainly divided into four phases: the slim disk phase (with time ≲ 1 yr), the inner slim plus outer thin disk phase ($\sim 10-\DP{6}$ yr), the thin disk phase ($\sim \DP{2}-\DP{7}$ yr), and the inner advection-dominated accretion flow plus outer thin disk phase, given the initial disk mass $\sim 0.05-0.5\,M_{\sun}$ and the disk formation time 10−3−1 s. Considering possible wind mass loss from the disk, we present both analytic formulae and numerically calculated results for the disk evolution, which is sensitive to the condition that determines the location of the outer disk radius. The systems are shown to be very bright in X-rays in the early phase, but quickly become transient within ≲ 100 yr, with peak luminosities decreasing with time. We suggest that they might account for part of the very faint X-ray transients around the Galactic center region, which generally require a very low mass transfer rate.

Chemical Tracers of Pre-Brown Dwarf Cores Formed Through Turbulent Fragmentation

Chemical Tracers of Pre-Brown Dwarf Cores Formed Through Turbulent Fragmentation

Authors:

Holdship et al

Abstract:

A gas-grain time dependent chemical code, UCL\_CHEM, has been used to investigate the possibility of using chemical tracers to differentiate between the possible formation mechanisms of brown dwarfs. In this work, we model the formation of a pre-brown dwarf core through turbulent fragmentation by following the depth-dependent chemistry in a molecular cloud through the step change in density associated with an isothermal shock and the subsequent freefall collapse once a bound core is produced. Trends in the fractional abundance of molecules commonly observed in star forming cores are then explored to find a diagnostic for identifying brown dwarf mass cores formed through turbulence. We find that the cores produced by our models would be bright in CO and NH3 but not in HCO+. This differentiates them from models using purely freefall collapse as such models produce cores that would have detectable transitions from all three molecules.

Thursday, December 17, 2015

HAT-P-57b: a hot Jupiter Around a Rapidly Rotating A8V Host Star

HAT-P-57b: A Short-Period Giant Planet Transiting A Bright Rapidly Rotating A8V Star Confirmed Via Doppler Tomography

Authors:

Hartman et al

Abstract:

We present the discovery of HAT-P-57b, a P = 2.4653 day transiting planet around a V = 10.465 +- 0.029 mag, Teff = 7500 +- 250 K main sequence A8V star with a projected rotation velocity of v sin i = 102.1 +- 1.3 km s^-1. We measure the radius of the planet to be R = 1.413 +- 0.054 R_J and, based on RV observations, place a 95% confidence upper limit on its mass of M < 1.85 M_J . Based on theoretical stellar evolution models, the host star has a mass and radius of 1.47 +- 0.12 M_sun, and 1.500 +- 0.050 R_sun, respectively. Spectroscopic observations made with Keck-I/HIRES during a partial transit event show the Doppler shadow of HAT-P-57b moving across the average spectral line profile of HAT-P- 57, confirming the object as a planetary system. We use these observations, together with analytic formulae that we derive for the line profile distortions, to determine the projected angle between the spin axis of HAT-P-57 and the orbital axis of HAT-P-57b. The data permit two possible solutions, with -16.7 deg < lambda < 3.3 deg or 27.6 deg < lambda < 57.4 deg at 95% confidence, and with relative probabilities for the two modes of 26% and 74%, respectively. Adaptive optics imaging with MMT/Clio2 reveals an object located 2.7" from HAT-P-57 consisting of two point sources separated in turn from each other by 0.22". The H and L -band magnitudes of the companion stars are consistent with their being physically associated with HAT-P-57, in which case they are stars of mass 0.61 +- 0.10 M_sun and 0.53 +- 0.08 M_sun. HAT-P-57 is the most rapidly rotating star, and only the fourth main sequence A star, known to host a transiting planet.

Do Hot Jupiter Systems Have Low Mass Stellar Companions Within 100 AU?

Friends of Hot Jupiters III: An Infrared Spectroscopic Search for Low-Mass Stellar Companions

Authors:

Piskorz et al

Abstract:

Surveys of nearby field stars indicate that stellar binaries are common, yet little is known about the effects that these companions may have on planet formation and evolution. The Friends of Hot Jupiters project uses three complementary techniques to search for stellar companions to known planet-hosting stars: radial velocity monitoring, adaptive optics imaging, and near-infrared spectroscopy. In this paper, we examine high-resolution K band infrared spectra of fifty stars hosting gas giant planets on short-period orbits. We use spectral fitting to search for blended lines due to the presence of cool stellar companions in the spectra of our target stars, where we are sensitive to companions with temperatures between 3500-5000 K and projected separations less than 100 AU in most systems. We identify eight systems with candidate low-mass companions, including one companion that was independently detected in our AO imaging survey. For systems with radial velocity accelerations, a spectroscopic non-detection rules out scenarios involving a stellar companion in a high inclination orbit. We use these data to place an upper limit on the stellar binary fraction at small projected separations, and show that the observed population of candidate companions is consistent with that of field stars and also with the population of wide-separation companions detected in our previous AO survey. We find no evidence that spectroscopic stellar companions are preferentially located in systems with short-period gas giant planets on eccentric and/or misaligned orbits.

Misaligned hot Jupiters can be Produced by Stellar Encounters

Generation of highly inclined protoplanetary discs through single stellar flybys

Authors:

Xiang-Gruess et al

Abstract:

We study the three-dimensional evolution of a viscous protoplanetary disc which is perturbed by a passing star on a parabolic orbit. The aim is to test whether a single stellar flyby is capable to excite significant disc inclinations which would favour the formation of so-called misaligned planets. We use smoothed particle hydrodynamics to study inclination, disc mass and angular momentum changes of the disc for passing stars with different masses. We explore different orbital configurations for the perturber's orbit to find the parameter spaces which allow significant disc inclination generation. Prograde inclined parabolic orbits are most destructive leading to significant disc mass and angular momentum loss. In the remaining disc, the final disc inclination is only below 20∘. This is due to the removal of disc particles which have experienced the strongest perturbing effects. Retrograde inclined parabolic orbits are less destructive and can generate disc inclinations up to 60∘. The final disc orientation is determined by the precession of the disc angular momentum vector about the perturber's orbital angular momentum vector and by disc orbital inclination changes.

We propose a sequence of stellar flybys for the generation of misalignment angles above 60∘. The results taken together show that stellar flybys are promising and realistic for the explanation of misaligned Hot Jupiters with misalignment angles up to 60\degr.

Wednesday, December 16, 2015

Wolf 1061c, a SuperEarth/Mini Neptune Orbiting 14 Light Years Away Reported

The search is on for a second 'Earth' that humans could colonise and now there's a new candidate - Wolf 1061c.

The rocky orb, more than four times the mass of the Earth, is the closest potentially habitable planet found outside our solar system so far, orbiting a star just 14 light years away.

It is one of three detected by Australian astronomers that orbit a red dwarf star called Wolf 1061.

On the Rotation of Co-orbital Bodies in Eccentric Orbits

On the rotation of co-orbital bodies in eccentric orbits

Authors:

Leleu et al

Abstract:

We investigate the resonant rotation of co-orbital bodies in eccentric and planar orbits. We develop a simple analytical model to study the impact of the eccentricity and orbital perturbations on the spin dynamics. We show there are three different families of spin-orbit resonances, one depending on the eccentricity, one depending on the orbital libration frequency, and another depending on the motion of the pericenter. The final rotation can be captured in any of these resonances. In some regions of the phase space the resonant islands may overlap, giving rise to chaotic rotation.

How Common are Nemesis Class Gas Giants and Brown Dwarfs Around G Dwarf Stars?

The VLT/NaCo large program to probe the occurrence of exoplanets and brown dwarfs at wide orbits. III. The frequency of brown dwarfs and giant planets as companions to solar-type stars

Authors:

Reggiani et al

Abstract:

In recent years there have been many attempts to characterize the occurrence of stellar, BD and planetary-mass companions to solar-type stars, with the aim of constraining formation mechanisms. From RV observations a dearth of companions with masses between 10-40 MJup has been noticed at close separations, suggesting the possibility of a distinct formation mechanism for objects above and below this range. We present a model for the substellar companion mass function (CMF). It consists of the superposition of the planet and BD companion mass distributions, assuming that we can extrapolate the RV measured companion mass function for planets to larger separations and the stellar companion mass-ratio distribution over all separations into the BD mass regime. By using both the results of the VLT/NaCo large program and the complementary archive datasets that probe the occurrence of planets and BDs on wide orbits around solar-type stars, we place some constraints on the planet and BD distributions. We developed a MC simulation tool to predict the outcome of a given survey, depending on the shape of the orbital parameter distributions. Comparing the predictions with the results of the observations, we calculate how likely different models are and which can be ruled out. Current observations are consistent with the proposed model for the CMF, as long as a sufficiently small outer truncation radius is introduced for the planet separation distribution. The results of the direct imaging surveys searching for substellar companions around Sun-like stars are consistent with a combined substellar mass spectrum of planets and BDs. This mass distribution has a minimum between 10 and 50 MJup, in agreement with RV measurements. The dearth of objects in this mass range would naturally arise from the shape of the mass distribution, without the introduction of any distinct formation mechanism for BDs.

Hydrogen-Water Mixtures in Giant Planet Interiors

Hydrogen-Water Mixtures in Giant Planet Interiors Studied with Ab Initio Simulations

Authors:

Soubiran et al

Abstract:

We study water-hydrogen mixtures under planetary interior conditions using ab initio molecular dynamics simulations. We determine the thermodynamic properties of various water-hydrogen mixing ratios at temperatures of 2000 and 6000 K for pressures of a few tens of GPa. These conditions are relevant for ice giant planets and for the outer envelope of the gas giants. We find that at 2000 K the mixture is in a molecular regime, while at 6000 K the dissociation of hydrogen and water is important and affects the thermodynamic properties. We study the structure of the liquid and analyze the radial distribution function. We provide estimates for the transport properties, diffusion and viscosity, based on autocorrelation functions. We obtained viscosity estimates of the order of a few tenths of mPa.s for the conditions under consideration. These results are relevant for dynamo simulations of ice giant planets.

Tuesday, December 15, 2015

The First Crowd Sourced ExoPlanet Names on a Poster

I have to say I am leery of this, honestly.  I can't help but feel the discoverers ought to be naming the exoplanets.

Detectability of Circumbinary ExoPlanets With Microlensing

Caustic Structures and Detectability of Circumbinary Planets in Microlensing

Authors:

Luhn et al

Abstract:

Recent discoveries of circumbinary planets in Kepler data show that there is a viable channel of planet formation around binary main sequence stars. Motivated by these discoveries, we have investigated the caustic structures and detectability of circumbinary planets in microlensing events. We have produced a suite of animations of caustics as a function of the projected separation and angle of the binary host to efficiently explore caustic structures over the entire circumbinary parameter space. Aided by these animations, we have derived a semi-empirical analytic expression for the location of planetary caustics, which are displaced in circumbinary lenses relative to those of planets with a single host. We have used this expression to show that the dominant source of caustic motion will be due to the planet's orbital motion and not that of the binary star. Finally, we estimate the fraction of circumbinary microlensing events that are recognizable as such to be significant (5-50 percent) for binary projected separations in the range 0.1-0.5 in units of Einstein radii.

The Solar System Terrestrial Planets Formed AFTER Jupiter and Saturn Reached Their Current Orbits

The Fragility of the Terrestrial Planets During a Giant Planet Instability

Authors:

Kaib et al

Abstract:

Many features of the outer solar system are replicated in numerical simulations if the giant planets undergo an orbital instability that ejects one or more ice giants. During this instability, Jupiter and Saturn's orbits diverge, crossing their 2:1 mean motion resonance (MMR), and this resonance-crossing can excite the terrestrial planet orbits. Using a large ensemble of simulations of this giant planet instability, we directly model the evolution of the terrestrial planet orbits during this process, paying special attention to systems that reproduce the basic features of the outer planets. In systems that retain four giant planets and finish with Jupiter and Saturn beyond their 2:1 MMR, we find at least an 85% probability that at least one terrestrial planet is lost. Moreover, systems that manage to retain all four terrestrial planets often finish with terrestrial planet eccentricities and inclinations larger than the observed ones. There is less than a ~5% chance that the terrestrial planet orbits will have a level of excitation comparable to the observed orbits. If we factor in the probability that the outer planetary orbits are well-replicated, we find a probability of 1% or less that the orbital architectures of the inner and outer planets are simultaneously reproduced in the same system. These small probabilities raise the prospect that the giant planet instability occurred before the terrestrial planets had formed. This scenario implies that the giant planet instability is not the source of the Late Heavy Bombardment and that terrestrial planet formation finished with the giant planets in their modern configuration.

The Compositional Evolution of Terrestrial Planets During Formation

COMPOSITIONAL EVOLUTION DURING ROCKY PROTOPLANET ACCRETION

Authors:

Carter et al

Abstract:

The Earth appears non-chondritic in its abundances of refractory lithophile elements, posing a significant problem for our understanding of its formation and evolution. It has been suggested that this non-chondritic composition may be explained by collisional erosion of differentiated planetesimals of originally chondritic composition. In this work, we present N-body simulations of terrestrial planet formation that track the growth of planetary embryos from planetesimals. We simulate evolution through the runaway and oligarchic growth phases under the Grand Tack model and in the absence of giant planets. These simulations include a state-of-the-art collision model that allows multiple collision outcomes, such as accretion, erosion, and bouncing events, and enables tracking of the evolving core mass fraction of accreting planetesimals. We show that the embryos grown during this intermediate stage of planet formation exhibit a range of core mass fractions, and that with significant dynamical excitation, enough mantle can be stripped from growing embryos to account for the Earth's non-chondritic Fe/Mg ratio. We also find that there is a large diversity in the composition of remnant planetesimals, with both iron-rich and silicate-rich fragments produced via collisions.

Monday, December 14, 2015

Hot Jupiters' Water is Hidden by Clouds

Exeter academics led an international team of experts in analysing observations from the NASA/ESA Hubble Space Telescope and the NASA Spitzer Space Telescope. Their combined power gave a detailed study of the atmospheres of 10 hot-Jupiter exoplanets - the largest number ever collectively studied - in a bid to understand their atmospheres. Previously, scientists had been puzzled that they had not observed water on some of these planets - but the latest study, published in Nature on Monday December 14, has revealed that their view of the water was only obscured by haze and cloud. Although no life could ever exist on such gaseous hot planets, the presence of water has significant implications for theories over how they were formed.

Known as "hot Jupiters", these gaseous planets share characteristics with Jupiter. However, they orbit very close to their stars, making their surface hot, and the planets difficult to study in detail without being overwhelmed by bright starlight. Because of this difficulty, Hubble has only explored a handful of hot Jupiters in the past.

Professor David Sing, of the University of Exeter, who led the study, said: "I'm really excited to finally 'see' this wide group of planets together, as this is the first time we've had sufficient wavelength coverage to compare multiple features from one planet to another. We found the planetary atmospheres to be much more diverse than we expected, and this significantly progresses our understanding of what makes up these planets and how they were created."

All of the planets have an orbit that brings them between their parent star and Earth. As the exoplanet passes in front of its host star, as seen from Earth, some of this starlight travels through the planet's outer atmosphere. "The atmosphere leaves its unique fingerprint on the starlight, which we can study when the light reaches us," explains co-author Dr Hannah Wakeford, a postgraduate student at the University of Exeter during the study who is now at NASA Goddard Space Flight Center, USA.

These fingerprints allowed the team to extract the signatures from various elements and molecules -- including water -- and distinguish between cloudy and cloud-free exoplanets.

The team's models revealed that, while apparently cloud-free exoplanets showed strong signs of water, the atmospheres of those hot Jupiters with faint water signals also contained clouds and haze -- both of which are known to hide water from view.

Kepler-36b's Planetary Interior is Probably Similar to Earth's

Scaling the Earth: A Sensitivity Analysis of Terrestrial Exoplanetary Interior Models

Authors:

Unterborn et al

Abstract:

An exoplanet's structure and composition are first-order controls of the planet's habitability. We explore which aspects of bulk terrestrial planet composition and interior structure affect the chief observables of an exoplanet: its mass and radius. We apply these perturbations to the Earth, the planet we know best. Using the mineral physics toolkit BurnMan to self-consistently calculate mass-radius models, we find that core radius, presence of light elements in the core and an upper-mantle consisting of low-pressure silicates have the largest effect on the final calculated mass at a given radius, with mantle composition being secondary. We further apply this model to determine the interior composition of Kepler-36b, finding that it is likely structurally similar to the Earth with Si/Fe = 1.14 compared to Earth's Si/Fe = 1 and Sun's Si/Fe = 1.19. We expand these results provide a grid of terrestrial mass-radius models for determining whether exoplanets are indeed "Earth-like" as bound by their composition and structure.

Lightning and the Generation of Organics in Exoplanetary Atmospheres

A Chemical Kinetics Network for Lightning and Life in Planetary Atmospheres

Authors:

Rimmer et al

Abstract:

There are many open questions about prebiotic chemistry in both planetary and exoplanetary environments. The increasing number of known exoplanets and other ultra-cool, substellar objects has propelled the desire to detect life and prebiotic chemistry outside the solar system. We present an ion-neutral chemical network constructed from scratch, Stand2015, that treats hydrogen, nitrogen, carbon and oxygen chemistry accurately within a temperature range between 100 K and 30000 K. Formation pathways for glycine and other organic molecules are included. The network is complete up to H6C2N2O3. Stand2015 is successfully tested against atmospheric chemistry models for HD209458b, Jupiter and the present-day Earth using a simple 1D photochemistry/diffusion code. Our results for the early Earth agree with those of Kasting (1993) for CO2, H2, CO and O2, but do not agree for water and atomic oxygen. We use the network to simulate an experiment where varied chemical initial conditions are irradiated by UV light. The result from our simulation is that more glycine is produced when more ammonia and methane is present. Very little glycine is produced in the absence of any molecular nitrogen and oxygen. This suggests that production of glycine is inhibited if a gas is too strongly reducing. Possible applications and limitations of the chemical kinetics network are also discussed.