Free Floating Gas Giant OTS44 has a Circum Planetary Disk

First millimeter detection of the disk around a young, isolated, planetary-mass object

Authors:

Bayo et al

Abstract:

OTS44 is one of only four free-floating planets known to have a disk. We have previously shown that it is the coolest and least massive known free-floating planet (∼12 MJup) with a substantial disk that is actively accreting. We have obtained Band 6 (233 GHz) ALMA continuum data of this very young disk-bearing object. The data shows a clear unresolved detection of the source. We obtained disk-mass estimates via empirical correlations derived for young, higher-mass, central (substellar) objects. The range of values obtained are between 0.07 and 0.63 M⊕ (dust masses). We compare the properties of this unique disk with those recently reported around higher-mass (brown dwarfs) young objects in order to infer constraints on its mechanism of formation. While extreme assumptions on dust temperature yield disk-mass values that could slightly diverge from the general trends found for more massive brown dwarfs, a range of sensible values provide disk masses compatible with a unique scaling relation between Mdust and M∗ through the substellar domain down to planetary masses.

The Demographics of Rocky Free-floating Planets and their Detectability by WFIRST

The Demographics of Rocky Free-floating Planets and their Detectability by WFIRST

Authors:

Barclay et al

Abstract:

Planets are thought to form via accretion from a remnant disk of gas and solids around a newly formed star. During this process, material in the disk either remains bound to the star as part of either a planet, a smaller celestial body, or makes up part of the the interplanetary medium; falls into the star; or is ejected from the system. Herein we use dynamical models to probe the abundance and properties of ejected material during late-stage planet formation and estimate their contribution to the free-floating planet population. We present 300 N-body simulations of terrestrial planet formation around a solar-type star, with and without giant planets present, using a model that accounts for collisional fragmentation. In simulations with Jupiter and Saturn analogs, about one-third of the initial (~5 M ⊕) disk mass is ejected, about half in planets more massive than Mercury but with a mass lower than 0.3 M ⊕, and the remainder in smaller bodies. Most ejections occur within 25 Myr, which is shorter than the timescale typically required for Earth-mass planets to grow (30–100 Myr). When giant planets are omitted from our simulations, almost no material is ejected within 200 Myr and only about 1% of the initial disk is ejected by 2 Gyr. We show that about 2.5 terrestrial-mass planets are ejected per star in the Galaxy. We predict that the space-borne microlensing search for free-floating planets from the Wide-Field Infra-Red Space Telescope will discover up to 15 Mars-mass planets, but few free-floating Earth-mass planets.

Capture of free-floating planets by stellar systems

Capture of free-floating planets by stellar systems

Authors:

Goulinski et al

Abstract:

Evidence of exoplanets with orbits that are misaligned with the spin of the host star may suggest that not all bound planets were born in the protoplanetary disk of their current planetary system. Observations have shown that free-floating Jupiter-mass objects can exceed the number of stars in our galaxy, implying that capture scenarios may not be so rare. To address this issue, we construct a three-dimensional simulation of a three-body scattering between a free-floating planet and a star accompanied by a Jupiter-mass bound planet. We distinguish between three different possible scattering outcomes, where the free-floating planet may get captured after the interaction with the binary, remain unbound, or "kick-out" the bound planet and replace it. The simulation was performed for different masses of the free-floating planets and stars, as well as different impact parameters, inclination angles and approach velocities. The outcome statistics are used to construct an analytical approximation of the cross section for capturing a free-floating planet by fitting their dependence on the tested variables. The analytically approximated cross section is used to predict the capture rate for these kinds of objects, and to estimate that about 1\% of all stars are expected to experience a temporary capture of a free-floating planet during their lifetime. Finally, we propose additional physical processes that may increase the capture statistics and whose contribution should be considered in future simulations.

A Massive Jupiter orbiting the very low metallicity giant star BD+03 2562 and a possible planet around HD 103485

Tracking Advanced Planetary Systems (TAPAS) with HARPS-N. V.: A Massive Jupiter orbiting the very low metallicity giant star BD+03 2562 and a possible planet around HD~103485

Authors:

Villaver et al

Abstract:
We present two evolved stars from the TAPAS (Tracking Advanced PlAnetary Systems) with HARPS-N project devoted to RV precision measurements of identified candidates within the PennState - Torun Centre for Astronomy Planet Search. Evolved stars with planets are crucial to understand the dependency of the planet formation mechanism on the mass and metallicity of the parent star and to study star-planet interactions. The paper is based on precise radial velocity (RV) measurements, for HD 103485 we collected 57 epochs over 3317 days with the Hobby-Eberly Telescope and its High Resolution Spectrograph and 18 ultra-precise HARPS-N data over 919 days. For BD+03 2562 we collected 46 epochs of HET data over 3380 days and 19 epochs of HARPS-N data over 919 days. We present the analysis of the data and the search for correlations between the RV signal and stellar activity, stellar rotation and photometric variability. Based on the available data, we interpret the RV variations measured in both stars as Keplerian motion. Both stars have masses close to Solar (1.11 and 1.14), very low metallicities ([Fe/H]=-0.50 and -0.71), and, both have Jupiter planetary mass companions (m sin i=7 and 6.4 Mj), in close to terrestrial orbits (1.4 and 1.3~au), with moderate eccentricities (e=0.34 and 0.2). However, we cannot totally exclude that the signal in the case of HD~103485 is due to rotational modulation of active regions. Based on the current data, we conclude that BD+03 2562 has a bona fide planetary companion while for HD 103485 we cannot totally exclude that the best explanation for the RV signal modulations is not the existence of a planet but stellar activity. If, the interpretation remains that both stars have planetary companions they represent systems orbiting very evolved stars with very low metallicities, a challenge to the conditions required for the formation of massive giant gas planets.

Giant Planets Can Act As Stabilizing Agents on Debris Disks

Giant Planets Can Act As Stabilizing Agents on Debris Disks

Authors:

Muñoz-Gutiérrez et al

Abstract:
We have explored the evolution of a cold debris disk under the gravitational influence of dwarf planet sized objects (DPs), both in the presence and absence of an interior giant planet. Through detailed long-term numerical simulations, we demonstrate that, when the giant planet is not present, DPs can stir the eccentricities and inclinations of disk particles, in linear proportion to the total mass of the DPs; on the other hand, when the giant planet is included in the simulations, the stirring is approximately proportional to the mass squared. This creates two regimes: below a disk mass threshold (defined by the total mass of DPs), the giant planet acts as a stabilizing agent of the orbits of cometary nucleii, diminishing the effect of the scatterers; above the threshold, the giant contributes to the dispersion of the particles.

MOA-2016-BLG-227Lb: A Massive Planet Characterized by Combining Light-curve Analysis and Keck AO Imaging

MOA-2016-BLG-227Lb: A Massive Planet Characterized by Combining Light-curve Analysis and Keck AO Imaging 

Authors:

Koshimoto et al 

Abstract:
We report the discovery of a microlensing planet—MOA-2016-BLG-227Lb—with a large planet/host mass ratio of q sime 9 × 10−3. This event was located near the K2 Campaign 9 field that was observed by a large number of telescopes. As a result, the event was in the microlensing survey area of a number of these telescopes, and this enabled good coverage of the planetary light-curve signal. High angular resolution adaptive optics images from the Keck telescope reveal excess flux at the position of the source above the flux of the source star, as indicated by the light-curve model. This excess flux could be due to the lens star, but it could also be due to a companion to the source or lens star, or even an unrelated star. We consider all these possibilities in a Bayesian analysis in the context of a standard Galactic model. Our analysis indicates that it is unlikely that a large fraction of the excess flux comes from the lens, unless solar-type stars are much more likely to host planets of this mass ratio than lower mass stars. We recommend that a method similar to the one developed in this paper be used for other events with high angular resolution follow-up observations when the follow-up observations are insufficient to measure the lens–source relative proper motion.

HD 20794 has at Least Three Exoplanets

Evidence for at least three planet candidates orbiting HD20794

Authors:

Feng et al

Abstract:

We explore the feasibility of detecting Earth analogs around Sun-like stars using the radial velocity method by investigating one of the largest radial velocities datasets for the one of the most stable radial-velocity stars HD20794. We proceed by disentangling the Keplerian signals from correlated noise and activity-induced variability. We diagnose the noise using the differences between radial velocities measured at different wavelength ranges, so-called "differential radial velocities". We apply this method to the radial velocities measured by HARPS, and identify four signals at 18, 89, 147 and 330 d. The two signals at periods of 18 and 89 d are previously reported and are better quantified in this work. The signal at a period of about 147 d is reported for the first time, and corresponds to a super-Earth with a minimum mass of 4.59 Earth mass located 0.51 AU from HD20794. We also find a significant signal at a period of about 330 d corresponding to a super-Earth or Neptune in the habitable zone. Since this signal is close to the annual sampling period and significant periodogram power in some noise proxies are found close to this signal, further observations and analyses are required to confirm it. The analyses of the eccentricity and consistency of signals provide weak evidence for the existence of the previously reported 43 d signal and a new signal at a period of about 11.9 d with a semi amplitude of 0.4 m/s. We find that the detection of a number of signals with radial velocity variations around 0.5\,m/s likely caused by low mass planet candidates demonstrates the important role of noise modeling in searching for Earth analogs.

HD 3167d: Another SuperEarth/Mini Neptune in the System?

Three's Company: An additional non-transiting super-Earth in the bright HD 3167 system, and masses for all three planets

Authors:

Christiansen et al

Abstract:

HD 3167 is a bright (V = 8.9), nearby K0 star observed by the NASA K2 mission (EPIC 220383386), hosting two small, short-period transiting planets. Here we present the results of a multi-site, multi-instrument radial velocity campaign to characterize the HD 3167 system. The masses of the transiting planets are 5.02+/-0.38 MEarth for HD 3167 b, a hot super-Earth with a likely rocky composition (rho_b = 5.60+2.15-1.43 g/cm^3), and 9.80+1.30-1.24 MEarth for HD 3167 c, a warm sub-Neptune with a likely substantial volatile complement (rho_c = 1.97+0.94-0.59 g/cm^3). We explore the possibility of atmospheric composition analysis and determine that planet c is amenable to transmission spectroscopy measurements, and planet b is a potential thermal emission target. We detect a third, non-transiting planet, HD 3167 d, with a period of 8.509+/-0.045 d (between planets b and c) and a minimum mass of 6.90+/-0.71 MEarth. We are able to constrain the mutual inclination of planet d with planets b and c: we rule out mutual inclinations below 1.3 degrees as we do not observe transits of planet d. From 1.3-40 degrees, there are viewing geometries invoking special nodal configurations which result in planet d not transiting some fraction of the time. From 40-60 degrees, Kozai-Lidov oscillations increase the system's instability, but it can remain stable for up to 100Myr. Above 60 degrees, the system is unstable. HD 3167 promises to be a fruitful system for further study and a preview of the many exciting systems expected from the upcoming NASA TESS mission.

HD 3167 System has a SuperEarth & Mini Neptune

The transiting multi-planet system HD3167: a 5.7 MEarth Super-Earth and a 8.3 MEarth mini-Neptune

Authors:

Gandolfi et al

Abstract: 

HD3167 is a bright (V=8.9 mag) K0V star observed by the NASA's K2 space mission during its Campaign 8. It has been recently found to host two small transiting planets, namely, HD3167b, an ultra short period (0.96 d) super-Earth, and HD3167c, a mini-Neptune on a relatively long-period orbit (29.85 d). Here we present an intensive radial velocity follow-up of HD3167 performed with the FIES@NOT, HARPS@ESO-3.6m, and HARPS-N@TNG spectrographs. We revise the system parameters and determine radii, masses, and densities of the two transiting planets by combining the K2 photometry with our spectroscopic data. With a mass of 5.69+/-0.44 MEarth, radius of 1.574+/-0.054 REarth, and mean density of 8.00(+1.0)(-0.98) g/cm^3, HD3167b joins the small group of ultra-short period planets known to have a rocky terrestrial composition. HD3167c has a mass of 8.33 (+1.79)(-1.85) MEarth and a radius of 2.740(+0.106)(-0.100) REarth, yielding a mean density of 2.21(+0.56)(-0.53) g/cm^3, indicative of a planet with a composition comprising a solid core surrounded by a thick atmospheric envelope. The rather large pressure scale height (about 350 km) and the brightness of the host star make HD3167c an ideal target for atmospheric characterization via transmission spectroscopy across a broad range of wavelengths. We found evidence of additional signals in the radial velocity measurements but the currently available data set does not allow us to draw any firm conclusion on the origin of the observed variation.

Constraining the Compositions of the TRAPPIST-1 Planets to Trace Snow Lines and Migration in M Dwarf Disks

Constraining the Compositions of the TRAPPIST-1 Planets to Trace Snow Lines and Migration in M Dwarf Disks

Authors:

Unterborn et al

Abstract:

The TRAPPIST-1 system, containing 7 transiting planets with constrained masses and radii, offers a singular opportunity to understand planet formation in another system. Not only can individual planets' bulk compositions be inferred, variations in composition (with respect to distance from the star) probe the composition of the TRAPPIST-1 disk and test models of planet formation. Other studies have shown that many of the TRAPPIST-1 planets are lower in density than rock and must either possess thick atmospheres or substantial liquid water/ice. The small masses of the planets argue against atmospheres. We use our ExoPlex mass-radius software package to constrain the fraction of each planet mass that is water. While we concur that planets f and g contain substantial (>50wt%) water/ice, we find b must be ≥6−8wt% water, but c must be ≤6−8wt% water. Since volatile fraction should increase with distance, the simplest interpretation is that both b and c each contain ≈7wt% water. Planets formed outside the snow line of TRAPPIST-1's disk are expected to contain ∼50wt% water ice like f and g, but the much lower ice abundances of b and c imply they formed inside the snow line. The TRAPPIST-1 system is marked by multiple mean motion resonances; for this and other reasons, substantial inward migration of the planets to their present orbits is inferred. We calculate the location of the snow line in the TRAPPIST-1 disk as a function of time. Depending on how rapidly the planets formed, the TRAPPIST-1 planets are at 1/2 to 1/8 of their starting distances from the star. While we infer that b and c formed inside the snow line, they contain much more water than planets formed inside the snow line in the Solar System (Earth is less than 0.1 wt% water), implying that the volatile gradient in TRAPPIST-1 was more gradual than in the Solar System.

Understanding Oxygen as a Biosignature in the Context of Its Environment

Exoplanet Biosignatures: Understanding Oxygen as a Biosignature in the Context of Its Environment

Authors:

Meadows et al

Abstract:
Here we review how environmental context can be used to interpret whether O2 is a biosignature in extrasolar planetary observations. This paper builds on the overview of current biosignature research discussed in Schwieterman et al. (2017), and provides an in-depth, interdisciplinary example of biosignature identification and observation that serves as a basis for the development of the general framework for biosignature assessment described in Catling et al., (2017). O2 is a potentially strong biosignature that was originally thought to be an unambiguous indicator for life at high-abundance. We describe the coevolution of life with the early Earth's environment, and how the interplay of sources and sinks in the planetary environment may have resulted in suppression of O2 release into the atmosphere for several billion years, a false negative for biologically generated O2. False positives may also be possible, with recent research showing potential mechanisms in exoplanet environments that may generate relatively high abundances of atmospheric O2 without a biosphere being present. These studies suggest that planetary characteristics that may enhance false negatives should be considered when selecting targets for biosignature searches. Similarly our ability to interpret O2 observed in an exoplanetary atmosphere is also crucially dependent on environmental context to rule out false positive mechanisms. We describe future photometric, spectroscopic and time-dependent observations of O2 and the planetary environment that could increase our confidence that any observed O2 is a biosignature, and help discriminate it from potential false positives. By observing and understanding O2 in its planetary context we can increase our confidence in the remote detection of life, and provide a model for biosignature development for other proposed biosignatures.

Is Losing Mass the Solution to the Young Faint Sun Paradox?

The Faint Young Sun and Faint Young Stars Paradox

Author:

Martens

Abstract:
The purpose of this paper is to explore a resolution for the Faint Young Sun Paradox that has been mostly rejected by the community, namely the possibility of a somewhat more massive young Sun with a large mass loss rate sustained for two to three billion years. This would make the young Sun bright enough to keep both the terrestrial and Martian oceans from freezing, and thus resolve the paradox. It is found that a large and sustained mass loss is consistent with the well observed spin-down rate of Sun-like stars, and indeed may be required for it. It is concluded that a more massive young Sun must be considered a plausible hypothesis.

The Flying Saucer: Tomography of the thermal and density gas structure of an edge-on protoplanetary disk

The Flying Saucer: Tomography of the thermal and density gas structure of an edge-on protoplanetary disk

Authors:

Dutrey et al

Abstract:
Determining the gas density and temperature structures of protoplanetary disks is a fundamental task to constrain planet formation theories. This is a challenging procedure and most determinations are based on model-dependent assumptions. We attempt a direct determination of the radial and vertical temperature structure of the Flying Saucer disk, thanks to its favorable inclination of 90 degrees. We present a method based on the tomographic study of an edge-on disk. Using ALMA, we observe at 0.5" resolution the Flying Saucer in CO J=2-1 and CS J=5-4. This edge-on disk appears in silhouette against the CO J=2-1 emission from background molecular clouds in ρ Oph. The combination of velocity gradients due to the Keplerian rotation of the disk and intensity variations in the CO background as a function of velocity provide a direct measure of the gas temperature as a function of radius and height above the disk mid-plane. The overall thermal structure is consistent with model predictions, with a cold (less than 15−12 ~K), CO-depleted mid-plane, and a warmer disk atmosphere. However, we find evidence for CO gas along the mid-plane beyond a radius of about 200\,au, coincident with a change of grain properties. Such a behavior is expected in case of efficient rise of UV penetration re-heating the disk and thus allowing CO thermal desorption or favoring direct CO photo-desorption. CO is also detected up to 3-4 scale heights while CS is confined around 1 scale height above the mid-plane. The limits of the method due to finite spatial and spectral resolutions are also discussed. This method appears to be very promising to determine the gas structure of planet-forming disks, provided that the molecular data have an angular resolution which is high enough, of the order of 0.3−0.1" at the distance of the nearest star forming regions.

Using Ice and Dust Lines to Constrain the Surface Densities of Protoplanetary Disks

Using Ice and Dust Lines to Constrain the Surface Densities of Protoplanetary Disks

Authors:

Powell et al

Abstract:

We present a novel method for determining the surface density of protoplanetary disks through consideration of disk "dust lines," which indicate the observed disk radial scale at different observational wavelengths. This method relies on the assumption that the processes of particle growth and drift control the radial scale of the disk at late stages of disk evolution such that the lifetime of the disk is equal to both the drift timescale and growth timescale of the maximum particle size at a given dust line. We provide an initial proof of concept of our model through an application to the disk TW Hya and are able to estimate the disk dust-to-gas ratio, CO abundance, and accretion rate in addition to the total disk surface density. We find that our derived surface density profile and dust-to-gas ratio are consistent with the lower limits found through measurements of HD gas. The CO ice line also depends on surface density through grain adsorption rates and drift and we find that our theoretical CO ice line estimates have clear observational analogues. We further apply our model to a large parameter space of theoretical disks and find three observational diagnostics that may be used to test its validity. First, we predict that the dust lines of disks other than TW Hya will be consistent with the normalized CO surface density profile shape for those disks. Second, surface density profiles that we derive from disk ice lines should match those derived from disk dust lines. Finally, we predict that disk dust and ice lines will scale oppositely, as a function of surface density, across a large sample of disks.

Disk Masses around Solar-mass Stars are Underestimated by CO Observations

Disk Masses around Solar-mass Stars are Underestimated by CO Observations

Authors:

Yu et al

Abstract:

Gas in protostellar disks provides the raw material for giant planet formation and controls the dynamics of the planetesimal-building dust grains. Accurate gas mass measurements help map the observed properties of planet-forming disks onto the formation environments of known exoplanets. Rare isotopologues of carbon monoxide (CO) have been used as gas mass tracers for disks in the Lupus star-forming region, with an assumed interstellar CO/H2 abundance ratio. Unfortunately, observations of T-Tauri disks show that CO abundance is not interstellar, a finding reproduced by models that show CO abundance decreasing both with distance from the star and as a function of time. Here, we present radiative transfer simulations that assess the accuracy of CO-based disk mass measurements. We find that the combination of CO chemical depletion in the outer disk and optically thick emission from the inner disk leads observers to underestimate gas mass by more than an order of magnitude if they use the standard assumptions of interstellar CO/H2 ratio and optically thin emission. Furthermore, CO abundance changes on million-year timescales, introducing an age/mass degeneracy into observations. To reach a factor of a few accuracy for CO-based disk mass measurements, we suggest that observers and modelers adopt the following strategies: (1) select low-J transitions; (2) observe multiple CO isotopologues and use either intensity ratios or normalized line profiles to diagnose CO chemical depletion; and (3) use spatially resolved observations to measure the CO-abundance distribution.

Collisions between Sintered Icy Aggregates

Collisions between Sintered Icy Aggregates

Authors:

Sirono et al

Abstract:

Collisions between sintered icy dust aggregates are numerically simulated. If the temperature of an icy aggregate is sufficiently high, sintering promotes molecular transport and a neck between adjacent grains grows. This growth changes the mechanical responses of the neck. We included this effect in a simulation code, and conducted collisional simulations. For porous aggregates, the critical velocity for growth, below which the mass of an aggregate increases, decreased from 50 m s−1 for the non-sintered case to 20 m s−1. For compacted aggregates, the main collisional outcome is bouncing. These results come from the fact that the strength of the neck is increased by sintering. The numerical results suggest that the collisional growth of icy grain aggregates is strongly affected by sintering.

Scattering-Produced (Sub)millimeter Polarization in Inclined Disks

Scattering-Produced (Sub)millimeter Polarization in Inclined Disks: Optical Depth Effects, Near-Far Side Asymmetry, and Dust Settling 

Authors:

Yang et al

Abstract:
Disk polarization at (sub)millimeter wavelengths is being revolutionized by ALMA observationally, but its origin remains uncertain. Dust scattering was recently recognized as a potential contributor to polarization, although its basic properties have yet to be thoroughly explored. Here, we quantify the effects of optical depth on the scattering-induced polarization in inclined disks through a combination of analytical illustration, approximate semi-analytical modeling using formal solution to the radiative transfer equation, and Monte Carlo simulations. We find that the near-side of the disk is significantly brighter in polarized intensity than the far-side, provided that the disk is optically thick and that the scattering grains have yet to settle to the midplane. This asymmetry is the consequence of a simple geometric effect: the near-side of the disk surface is viewed more edge-on than the far-side. It is a robust signature that may be used to distinguish the scattering-induced polarization from that by other mechanisms, such as aligned grains. The asymmetry is weaker for a geometrically thinner dust disk. As such, it opens an exciting new window on dust settling. We find anecdotal evidence from dust continuum imaging of edge-on disks that large grains are not yet settled in the youngest (Class 0) disks, but become more so in older disks. This trend is corroborated by the polarization data in inclined disks showing that younger disks have more pronounced near-far side asymmetry and thus less grain settling. If confirmed, the trend would have far-reaching implications for grain evolution and, ultimately, the formation of planetesimals and planets.

A SOFIA FORCAST Grism Study of the Mineralogy of Dust in the Winds of Proto-planetary Nebulae: RV Tauri Stars and SRd Variables

A SOFIA FORCAST Grism Study of the Mineralogy of Dust in the Winds of Proto-planetary Nebulae: RV Tauri Stars and SRd Variables

Authors:

Arneson et al

Abstract:
We present a SOFIA FORCAST grism spectroscopic survey to examine the mineralogy of the circumstellar dust in a sample of post-asymptotic giant branch yellow supergiants that are believed to be the precursors of planetary nebulae. Our mineralogical model of each star indicates the presence of both carbon rich and oxygen rich dust species-contrary to simple dredge-up models-with a majority of the dust in the form of amorphous carbon and graphite. The oxygen rich dust is primarily in the form of amorphous silicates. The spectra do not exhibit any prominent crystalline silicate emission features. For most of the systems, our analysis suggests that the grains are relatively large and have undergone significant processing, supporting the hypothesis that the dust is confined to a Keplerian disk and that we are viewing the heavily processed, central regions of the disk from a nearly face-on orientation. These results help to determine the physical properties of the post-AGB circumstellar environment and to constrain models of post-AGB mass loss and planetary nebula formation.

The Viewing Geometry of Brown Dwarfs Influences Their Observed Colours and Variability Properties

The Viewing Geometry of Brown Dwarfs Influences Their Observed Colours and Variability Properties

Authors:

Vos et al

Abstract: 

In this paper we study the full sample of known Spitzer [3.6 μm] and J-band variable brown dwarfs. We calculate the rotational velocities, vsini, of 16 variable brown dwarfs using archival Keck NIRSPEC data and compute the inclination angles of 19 variable brown dwarfs. 

The results obtained show that all objects in the sample with mid-IR variability detections are inclined at an angle >20∘, while all objects in the sample displaying J-band variability have an inclination angle >35∘. J-band variability appears to be more affected by inclination than \textit{Spitzer} [3.6 μm] variability, and is strongly attenuated at lower inclinations. Since J-band observations probe deeper into the atmosphere than mid-IR observations, this effect may be due to the increased atmospheric path length of J-band flux at lower inclinations. 

We find a statistically significant correlation between the colour anomaly and inclination of our sample, where field objects viewed equator-on appear redder than objects viewed at lower inclinations. Considering the full sample of known variable L, T and Y spectral type objects in the literature, we find that the variability properties of the two bands display notably different trends, due to both intrinsic differences between bands and the sensitivity of ground-based versus space-based searches. However, in both bands we find that variability amplitude may reach a maximum at ∼7−9 hr periods. Finally, we find a strong correlation between colour anomaly and variability amplitude for both the J-band and mid-IR variability detections, where redder objects display higher variability amplitudes.

The Young L Dwarf 2MASS J11193254-1137466 is a Planetary-Mass Binary

The Young L Dwarf 2MASS J11193254-1137466 is a Planetary-Mass Binary

Authors:

Best et al

Abstract:
We have discovered that the extremely red, low-gravity L7 dwarf 2MASS J11193254-1137466 is a 0.14" (3.6 AU) binary using Keck laser guide star adaptive optics imaging. 2MASS J11193254-1137466 has previously been identified as a likely member of the TW Hydrae Association (TWA). Using our updated photometric distance and proper motion, a kinematic analysis based on the BANYAN II model gives an 82% probability of TWA membership. At TWA's 10±3 Myr age and using hot-start evolutionary models, 2MASS J11193254-1137466AB is a pair of 3.7+1.2−0.9 MJup brown dwarfs, making it the lowest-mass binary discovered to date. We estimate an orbital period of 90+80−50 years. One component is marginally brighter in K band but fainter in J band, making this a probable flux-reversal binary, the first discovered with such a young age. We also imaged the spectrally similar TWA L7 dwarf WISEA J114724.10-204021.3 with Keck and found no sign of binarity. Our evolutionary model-derived Teff estimate for WISEA J114724.10-204021.3 is ≈230 K higher than for 2MASS J11193254-1137466AB, at odds with their spectral similarity. This discrepancy suggests that WISEA J114724.10-204021.3 may actually be a tight binary with masses and temperatures very similar to 2MASS J11193254-1137466AB, or further supporting the idea that near-infrared spectra of young ultracool dwarfs are shaped by factors other than temperature and gravity. 2MASS J11193254-1137466AB will be an essential benchmark for testing evolutionary and atmospheric models in the young planetary-mass regime.

JVLA Observations of Young Brown Dwarfs

JVLA Observations of Young Brown Dwarfs

Authors:

Rodríguez et al

Abstract:
We present sensitive 3.0 cm JVLA radio continuum observations of six regions of low-mass star formation that include twelve young brown dwarfs (BDs) and four young BD candidates. We detect a total of 49 compact radio sources in the fields observed, of which 24 have no reported counterparts and are considered new detections. Twelve of the radio sources show variability in timescales of weeks to months, suggesting gyrosynchrotron emission produced in active magnetospheres. Only one of the target BDs, FU Tau A, was detected. However, we detected radio emission associated with two of the BD candidates, WL 20S and CHLT 2. The radio flux densities of the sources associated with these BD candidates are more than an order of magnitude larger than expected for a BD and suggest a revision of their classification. In contrast, FU Tau A falls on the well-known correlation between radio luminosity and bolometric luminosity, suggesting that the emission comes from a thermal jet and that this BD seems to be forming as a scaled-down version of low-mass stars.

Tidal dissipation in rotating low-mass stars and implications for the orbital evolution of close-in massive planets.

Tidal dissipation in rotating low-mass stars and implications for the orbital evolution of close-in massive planets. II. Effect of stellar metallicity

Authors:

Bolmont et al

Abstract:
Observations of hot Jupiter type exoplanets suggest that their orbital period distribution depends on the metallicity of their host star. We investigate here whether the impact of the stellar metallicity on the evolution of the tidal dissipation inside the convective envelope of rotating stars and its resulting effect on the planetary migration might be a possible explanation for this observed statistical trend.

We use a frequency-averaged tidal dissipation formalism coupled to an orbital evolution code and to rotating stellar evolution models to estimate the effect of a change of stellar metallicity on the evolution of close-in planets. We consider here two different stellar masses: 0.4 and 1.0 M⊙ evolving from the early pre-main sequence phase up to the red giant branch.

We show that the metallicity of a star has a strong effect on the stellar parameters which in turn strongly influence the tidal dissipation in the convective region. While on the pre-main sequence the dissipation of a metal poor Sun-like star is higher than the dissipation of a metal rich Sun-like star, on the main sequence it is the opposite. However, for the 0.4 M⊙ star, the dependence of the dissipation with metallicity is much less visible.

Using an orbital evolution model, we show that changing the metallicity leads to different orbital evolutions (e.g., planets migrate farther out from an initially fast rotating metal rich star). By using this model, we qualitatively reproduced the observational trends of the population of hot Jupiters with the metallicity of their host stars. However, more steps are needed to improve our model to try to quantitatively fit our results to the observations. Namely, we need to improve the treatment of the rotation evolution in the orbital evolution model and ultimately we need to consistently couple of the orbital model to the stellar evolution model.

Hot Jupiter WASP-12b's Orbit is Decaying

The Apparently Decaying Orbit of WASP-12b

Authors:
Patra et al

Abstract:

We present new transit and occultation times for the hot Jupiter WASP-12b. The data are compatible with a constant period derivative: $\dot{P}=-29\pm 3$ ms yr−1 and $P/\dot{P}=3.2\,\mathrm{Myr}$. However, it is difficult to tell whether we have observed orbital decay or a portion of a 14-year apsidal precession cycle. If interpreted as decay, the star's tidal quality parameter ${Q}_{\star }$ is about $2\times {10}^{5}$. If interpreted as precession, the planet's Love number is 0.44 ± 0.10. Orbital decay appears to be the more parsimonious model: it is favored by ${\rm{\Delta }}{\chi }^{2}=5.5$ despite having two fewer free parameters than the precession model. The decay model implies that WASP-12 was discovered within the final ~0.2% of its existence, which is an unlikely coincidence but harmonizes with independent evidence that the planet is nearing disruption. Precession does not invoke any temporal coincidence, but it does require some mechanism to maintain an eccentricity of $\approx 0.002$ in the face of rapid tidal circularization. To distinguish unequivocally between decay and precession will probably require a few more years of monitoring. Particularly helpful will be occultation timing in 2019 and thereafter.

A population study of hot Jupiter atmospheres

A population study of hot Jupiter atmospheres

Authors:

Tsiaras et al

Abstract:
We present here the analysis of 30 gaseous extrasolar planets, with temperatures between 600 and 2400 K and radii between 0.35 and 1.9 RJup. The quality of the HST/WFC3 spatially-scanned data combined with our specialised analysis tools, allows us to create the largest and most self-consistent sample of exoplanetary transmission spectra to date and study the collective behaviour of warm and hot gaseous planets rather than isolated case-studies. We define a new metric, the Atmospheric Detectability Index (ADI) to evaluate the statistical significance of an atmospheric detection and find statistically significant atmospheres around 16 planets. For most of the Jupiters in our sample we find the detectability of their atmospheres to be dependent on the planetary radius but not on the planetary mass. This indicates that planetary gravity is a secondary factor in the evolution of planetary atmospheres. We detect the presence of water vapour in all the statistically detectable atmospheres and we cannot rule out its presence in the atmospheres of the others. In addition, TiO and/or VO signatures are detected with 4σ confidence in WASP-76 b, and they are most likely present on WASP-121 b. We find no correlation between expected signal-to-noise and atmospheric detectability for most targets. This has important implications for future large-scale surveys.

On The Feasibility of Exomoon Detection Via Exoplanet Phase Curve Spectral Contrast

On The Feasibility of Exomoon Detection Via Exoplanet Phase Curve Spectral Contrast

Authors:

Forgan et al

Abstract:
An exoplanet-exomoon system presents a superposition of phase curves to observers - the dominant component varies according to the planetary period, and the lesser varies according to both the planetary and the lunar period. If the spectra of the two bodies differs significantly, then it is likely there are wavelength regimes where the contrast between the moon and planet is significantly larger. In principle, this effect could be used to isolate periodic oscillations in the combined phase curve. Being able to detect the exomoon component would allow a characterisation of the exomoon radius, and potentially some crude atmospheric data. We run a parameter survey of combined exoplanet-exomoon phase curves, which show that for most sets of planet-moon parameters, the lunar component of the phase curve is undetectable to current state-of-the-art transit observations. Even with future transit survey missions, measuring the exomoon signal will most likely require photometric precision of 10 parts per million or better. The only exception to this is if the moon is strongly tidally heated or in some way self-luminous. In this case, measurements of the phase curve at wavelengths greater than a few microns can be dominated by the lunar contribution. Instruments like the James Webb Space Telescope and its successors are needed to make this method feasible.

HD 106315c: a SubSaturn Detected by K2

Two Small Transiting Planets and a Possible Third Body Orbiting HD 106315

Authors:

Crossfield et al

Abstract:

The masses, atmospheric makeups, spin–orbit alignments, and system architectures of extrasolar planets can be best studied when the planets orbit bright stars. We report the discovery of three bodies orbiting HD 106315, a bright (V = 8.97 mag) F5 dwarf targeted by our K2 survey for transiting exoplanets. Two small transiting planets are found to have radii ${2.23}_{-0.25}^{+0.30}\,{R}_{\oplus }$ and ${3.95}_{-0.39}^{+0.42}\,{R}_{\oplus }$ and orbital periods 9.55 days and 21.06 days, respectively. A radial velocity (RV) trend of 0.3 ± 0.1 m s−1 day−1 indicates the likely presence of a third body orbiting HD 106315 with period gsim160 days and mass gsim45 M ⊕. Transits of this object would have depths gsim0.1% and are definitively ruled out. Although the star has v sin i = 13.2 km s−1, it exhibits a short-timescale RV variability of just 6.4 m s−1. Thus, it is a good target for RV measurements of the mass and density of the inner two planets and the outer object's orbit and mass. Furthermore, the combination of RV noise and moderate v sin i makes HD 106315 a valuable laboratory for studying the spin–orbit alignment of small planets through the Rossiter–McLaughlin effect. Space-based atmospheric characterization of the two transiting planets via transit and eclipse spectroscopy should also be feasible. This discovery demonstrates again the power of K2 to find compelling exoplanets worthy of future study.

OGLE-2013-BLG-1761Lb: A SuperJupiter Orbiting a M/K Dwarf Star

OGLE-2013-BLG-1761Lb: A Massive Planet around an M/K Dwarf 

Authors:
Hirao et al

Abstract:
We report the discovery and the analysis of the planetary microlensing event, OGLE-2013-BLG-1761. There are some degenerate solutions in this event because the planetary anomaly is only sparsely sampled. However, the detailed light-curve analysis ruled out all stellar binary models and shows the lens to be a planetary system. There is the so-called close/wide degeneracy in the solutions with the planet/host mass ratio of q ~ (7.0 ± 2.0) × 10−3 and q ~ (8.1 ± 2.6) × 10−3 with the projected separation in Einstein radius units of s = 0.95 (close) and s = 1.18 (wide), respectively. The microlens parallax effect is not detected, but the finite source effect is detected. Our Bayesian analysis indicates that the lens system is located ${D}_{{\rm{L}}}={6.9}_{-1.2}^{+1.0}\,\mathrm{kpc}$ away from us and the host star is an M/K dwarf with a mass of ${\text{}}{M}_{{\rm{L}}}={0.33}_{-0.19}^{+0.32}\,{\text{}}{M}_{\odot }$ orbited by a super-Jupiter mass planet with a mass of ${\text{}}{m}_{{\rm{P}}}={2.7}_{-1.5}^{+2.5}\,{M}_{\mathrm{Jup}}$ at the projected separation of ${a}_{\perp }={1.8}_{-0.5}^{+0.5}\,\mathrm{au}$. The preference of the large lens distance in the Bayesian analysis is due to the relatively large observed source star radius. The distance and other physical parameters may be constrained by the future high-resolution imaging by large ground telescopes or HST. If the estimated lens distance is correct, then this planet provides another sample for testing the claimed deficit of planets in the Galactic bulge.

K2-106 System: A Exoplanetary System With Two Very Different Worlds of the Same Mass

K2-106, a system containing a metal rich planet and a planet of lower density

Authors:

Guenther et al

Abstract:
Aims:

Planets in the mass-range from 2 to 15 MEarth are very diverse. Some of them have very low, others very high densities.

Method:

We determined the masses, radii and the densities for the two transiting planets orbiting K2-106, which have been previously found. The inner one is an ultra-short period planet with an orbital period of 0.57 days. The outer planet has orbital period of 13.3 days.

Results:

The two planets have similar masses, though very different densities. For K2-106b we derive M_p=7.69+/-0.82 MEarth, Rp=1.52+/-0.16 REarth, and a high density of 12.0 -3.2+4.8 gcm-3. For K2-106c, we find 6.79+/-2.29 MEarth, R_p=2.59+/-0.27 REarth and a relatively low density of 2.4-1.1+1.6 gcm-3.

Conclusions:

Since the systems contains two planets of almost the same mass, but different distances from the host star, it is an excellent laboratory to study atmospheric escape. Comparing the mass and radius of the inner planet with composition models implies that it has an iron core containing at least 50% of its mass. Such a high metal content is surprising, particularly given that the star has solar abundance. We discuss various formation scenarios for this unusual planet.

Formation of Close-in SuperEarths by Giant Impacts

Formation of Close-in Super-Earths by Giant Impacts: Effects of Initial Eccentricities and Inclinations of Protoplanets

Authors:
Matsumoto et al

Abstract:
Recent observations have revealed the eccentricity and inclination distributions of close-in super-Earths. These distributions have the potential to constrain their formation processes. In the in-situ formation scenario, the eccentricities and inclinations of planets are determined by gravitational scattering and collisions between protoplanets on the giant impact stage. We investigate the effect of the initial eccentricities and inclinations of protoplanets on the formation of close-in super-Earths. We perform N-body simulations of protoplanets in gas-free disks, changing the initial eccentricities and inclinations systematically. We find that while the eccentricities of protoplanets are well relaxed through their evolution, the inclinations are not. When the initial inclinations are small, they are not generally pumped up since scattering is less effective and collisions occur immediately after orbital crossing. On the other hand, when the initial inclinations are large, they tend to be kept large since collisional damping is less effective. Not only the resultant inclinations of planets, but also their number, eccentricities, angular momentum deficit, and orbital separations are affected by the initial inclinations of protoplanets.

MOA-2012-BLG-505Lb: A SuperEarth probably in the Galactic bulge

MOA-2012-BLG-505Lb: A super-Earth mass planet probably in the Galactic bulge

Authors:
Nagakane et al

Abstract:

We report the discovery of a super-Earth mass planet in the microlensing event MOA-2012-BLG-505. This event has the second shortest event timescale of tE=10±1 days where the observed data show evidence of planetary companion. Our 15 minute high cadence survey observation schedule revealed the short subtle planetary signature. The system shows the well known close/wide degeneracy. The planet/host-star mass ratio is q=2.1×10−4 and the projected separation normalized by the Einstein radius is s = 1.1 or 0.9 for the wide and close solutions, respectively. We estimate the physical parameters of the system by using a Bayesian analysis and find that the lens consists of a super-Earth with a mass of 6.7+10.7−3.6M⊕ orbiting around a brown-dwarf or late M-dwarf host with a mass of 0.10+0.16−0.05M⊙ with a projected star-planet separation of 0.9+0.3−0.2AU. The system is at a distance of 7.2±1.1 kpc, i.e., it is likely to be in the Galactic bulge. The small angular Einstein radius (θE=0.12±0.02 mas) and short event timescale are typical for a low-mass lens in the Galactic bulge. Such low-mass planetary systems in the Bulge are rare because the detection efficiency of planets in short microlensing events is relatively low. This discovery may suggest that such low mass planetary systems are abundant in the Bulge and currently on-going high cadence survey programs will detect more such events and may reveal an abundance of such planetary systems.

On the Spin States of Habitable Zone Exoplanets Around M Dwarfs: The Effect of a Near-Resonant Companion

On the Spin States of Habitable Zone Exoplanets Around M Dwarfs: The Effect of a Near-Resonant Companion


Authors:

Vinson et al

Abstract:
One longstanding problem for the potential habitability of planets within M dwarf systems is their likelihood to be tidally locked in a synchronously rotating spin state. This problem thus far has largely been addressed only by considering two objects: the star and the planet itself. However, many systems have been found to harbor multiple planets, with some in or very near to mean-motion resonances. The presence of a planetary companion near a mean-motion resonance can induce oscillatory variations in the mean-motion of the planet, which we demonstrate can have significant effects on the spin-state of an otherwise synchronously rotating planet. In particular, we find that a planetary companion near a mean-motion resonance can excite the spin states of planets in the habitable zone of small, cool stars, pushing otherwise synchronously rotating planets into higher amplitude librations of the spin state, or even complete circulation resulting in effective stellar days with full surface coverage on the order of years or decades. This increase in illuminated area can have potentially dramatic influences on climate, and thus on habitability. We also find that the resultant spin state can be very sensitive to initial conditions due to the chaotic nature of the spin state at early times within certain regimes. We apply our model to two hypothetical planetary systems inspired by the K00255 and TRAPPIST-1 systems, which both have Earth-sized planets in mean-motion resonances orbiting cool stars.

Habitable Moist Atmospheres On Terrestrial Planets Near the Inner Edge Of the Habitable Zone Around M-dwarfs

Habitable Moist Atmospheres On Terrestrial Planets Near the Inner Edge Of the Habitable Zone Around M-dwarfs

Authors:

Kopparapu et al

Abstract:
Terrestrial planets in the habitable zones (HZs) of low-mass stars and cool dwarfs have received significant scrutiny recently because their shorter orbital periods increase their chances of detection and characterization compared to planets around G-dwarfs. As these planets are likely tidal-locked, improved 3D numerical simulations of such planetary atmospheres are needed to guide target selection. Here we use a 3-D climate system model, updated with new water-vapor absorption coefficients derived from the HITRAN 2012 database, to study ocean covered planets at the inner edge of the HZ around late-M to mid-K stars (2600 K <= Teff <= 4500K). Our results indicate that these updated water-vapor coefficients result in significant warming compared to previous studies, so the inner HZ around M-dwarfs is not as close as suggested by earlier work. Assuming synchronously rotating planets, we find that planets at the inner HZ of stars with Teff > 3000K undergo the classical "moist-greenhouse" (H2O mixing ratio > 10-3 in the stratosphere) at significantly lower surface temperature (~ 280K) in our 3-D model compared with 1-D climate models (~ 340K). This implies that some planets around low mass stars can simultaneously undergo water-loss and remain habitable. However, for star with Teff <= 3000K, planets at the inner HZ may directly transition to a runaway state, while bypassing the moist greenhouse water-loss entirely. We analyze transmission spectra of planets in a moist green- house regime, and find that there are several prominent H2O features, including a broad feature between 5-8 microns, within JWST MIRI instrument range. Thus, relying only upon standard Earth-analog spectra with 24-hour rotation period around M-dwarfs for habitability studies will miss the strong H2O features that one would expect to see on synchronously rotating planets around M-dwarf stars, with JWST.

Is Kepler-452b Habitable?

Quantitative estimates of the surface habitability of Kepler-452b

Authors:

Silva et al

Abstract:
Kepler-452b is currently the best example of an Earth-size planet in the habitable zone of a sun-like star, a type of planet whose number of detections is expected to increase in the future. Searching for biosignatures in the supposedly thin atmospheres of these planets is a challenging goal that requires a careful selection of the targets. Under the assumption of a rocky-dominated nature for Kepler-452b, we considered it as a test case to calculate a temperature-dependent habitability index, h050, designed to maximize the potential presence of biosignature-producing activity (Silva et al.\ 2016). The surface temperature has been computed for a broad range of climate factors using a climate model designed for terrestrial-type exoplanets (Vladilo et al.\ 2015). After fixing the planetary data according to the experimental results (Jenkins et al.\ 2015), we changed the surface gravity, CO2 abundance, surface pressure, orbital eccentricity, rotation period, axis obliquity and ocean fraction within the range of validity of our model. For most choices of parameters we find habitable solutions with h050>0.2 only for CO2 partial pressure pCO2≲0.04\,bar. At this limiting value of CO2 abundance the planet is still habitable if the total pressure is p≲2\,bar. In all cases the habitability drops for eccentricity e≳0.3. Changes of rotation period and obliquity affect the habitability through their impact on the equator-pole temperature difference rather than on the mean global temperature. We calculated the variation of h050 resulting from the luminosity evolution of the host star for a wide range of input parameters. Only a small combination of parameters yield habitability-weighted lifetimes ≳2\,Gyr, sufficiently long to develop atmospheric biosignatures still detectable at the present time.

Analytic Expressions for the Inner-Rim Structure of Passively Heated Protoplanetary Disks

Analytic Expressions for the Inner-Rim Structure of Passively Heated Protoplanetary Disks

Authors:

Ueda et al

Abstract:
We analytically derive the expressions for the structure of the inner region of protoplanetary disks based on the results from the recent hydrodynamical simulations. The inner part of a disk can be divided into four regions: dust-free region with gas temperature in the optically thin limit, optically thin dust halo, optically thick condensation front and the classical optically thick region in order from the inside. We derive the dust-to-gas mass ratio profile in the dust halo using the fact that partial dust condensation regulates the temperature to the dust evaporation temperature. Beyond the dust halo, there is an optically thick condensation front where all the available silicate gas condenses out. The curvature of the condensation surface is determined by the condition that the surface temperature must be nearly equal to the characteristic temperature ∼1200K. We derive the mid-plane temperature in the outer two regions using the two-layer approximation with the additional heating by the condensation front for the outermost region. As a result, the overall temperature profile is step-like with steep gradients at the borders between the outer three regions. The borders might act as planet traps where the inward migration of planets due to gravitational interaction with the gas disk stops. The temperature at the border between the two outermost regions coincides with the temperature needed to activate magnetorotational instability, suggesting that the inner edge of the dead zone must lie at this border. The radius of the dead-zone inner edge predicted from our solution is ∼ 2-3 times larger than that expected from the classical optically thick temperature.

Exploring dust around HD 142527 down to 0.025" / 4au using SPHERE/ZIMPOL

Exploring dust around HD142527 down to 0.025" / 4au using SPHERE/ZIMPOL

Authors:

Avenhaus et al

Abstract:

We have observed the protoplanetary disk of the well-known young Herbig star HD 142527 using ZIMPOL Polarimetric Differential Imaging with the VBB (Very Broad Band, ~600-900nm) filter. We obtained two datasets in May 2015 and March 2016. Our data allow us to explore dust scattering around the star down to a radius of ~0.025" (~4au). The well-known outer disk is clearly detected, at higher resolution than before, and shows previously unknown sub-structures, including spirals going inwards into the cavity. Close to the star, dust scattering is detected at high signal-to-noise ratio, but it is unclear whether the signal represents the inner disk, which has been linked to the two prominent local minima in the scattering of the outer disk, interpreted as shadows. An interpretation of an inclined inner disk combined with a dust halo is compatible with both our and previous observations, but other arrangements of the dust cannot be ruled out. Dust scattering is also present within the large gap between ~30 and ~140au. The comparison of the two datasets suggests rapid evolution of the inner regions of the disk, potentially driven by the interaction with the close-in M-dwarf companion, around which no polarimetric signal is detected.

In situ accretion of gaseous envelopes on to planetary cores embedded in evolving protoplanetary discs

In situ accretion of gaseous envelopes on to planetary cores embedded in evolving protoplanetary discs

Authors:

Coleman et al

Abstract:
The core accretion hypothesis posits that planets with significant gaseous envelopes accreted them from their protoplanetary discs after the formation of rocky/icy cores. Observations indicate that such exoplanets exist at a broad range of orbital radii, but it is not known whether they accreted their envelopes in situ, or originated elsewhere and migrated to their current locations. We consider the evolution of solid cores embedded in evolving viscous discs that undergo gaseous envelope accretion in situ with orbital radii in the range 0.1−10au. Additionally, we determine the long-term evolution of the planets that had no runaway gas accretion phase after disc dispersal. We find: (i) Planets with 5M⊕ cores never undergo runaway accretion. The most massive envelope contained 2.8M⊕ with the planet orbiting at 10au. (ii) Accretion is more efficient onto 10M⊕ and 15M⊕ cores. For orbital radii ap≥0.5au, 15M⊕ cores always experienced runaway gas accretion. For ap≥5au, all but one of the 10M⊕ cores experienced runaway gas accretion. No planets experienced runaway growth at ap=0.1au. (iii) We find that, after disc dispersal, planets with significant gaseous envelopes cool and contract on Gyr time-scales, the contraction time being sensitive to the opacity assumed. Our results indicate that Hot Jupiters with core masses ≲15M⊕ at ≲0.1au likely accreted their gaseous envelopes at larger distances and migrated inwards. Consistently with the known exoplanet population, Super-Earths and mini-Neptunes at small radii during the disc lifetime, accrete only modest gaseous envelopes.

Binary Star Formation and the Outflows from their Disks

Binary Star Formation and the Outflows from their Discs

Authors:

Kuruwita et al

Abstract:
We carry out magnetohydrodynamical simulations with FLASH of the formation of a single, a tight binary (a∼2.5 AU) and a wide binary star (a∼45 AU). We study the outflows and jets from these systems to understand the contributions the circumstellar and circumbinary discs have on the efficiency and morphology of the outflow. In the single star and tight binary case we obtain a single pair of jets launched from the system, while in the wide binary case two pairs of jets are observed. This implies that in the tight binary case the contribution of the circumbinary disc on the outflow is greater than that in the wide binary case. We also find that the single star case is the most efficient at transporting mass, linear and angular momentum from the system, while the wide binary case is less efficient (∼50%,∼33%,∼42% of the respective quantities in the single star case). The tight binary's efficiency falls between the other two cases (∼71%,∼66%,∼87% of the respective quantities in the single star case). By studying the magnetic field structure we deduce that the outflows in the single star and tight binary star case are magnetocentrifugally driven, whereas in the wide binary star case the outflows are driven by a magnetic pressure gradient.

HD far infrared emission as a measure of protoplanetary disk mass

HD far infrared emission as a measure of protoplanetary disk mass

Authors:

Trapman et al

Abstract:
Protoplanetary disks around young stars are the sites of planet formation. While the dust mass can be estimated using standard methods, determining the gas mass - and thus the amount of material available to form giant planets - has proven to be very difficult. Hydrogen deuteride (HD) is a promising alternative to the commonly-used gas mass tracer, CO. We aim to examine the robustness of HD as tracer of the disk gas mass, specifically the effect of gas mass on the HD FIR emission and its sensitivity to the vertical structure. Deuterium chemistry reactions relevant for HD were implemented in the thermochemical code DALI and models were run for a range of disk masses and vertical structures. The HD J=1-0 line intensity depends directly on the gas mass through a sublinear power law relation with a slope of ~0.8. Assuming no prior knowledge about the vertical structure of a disk and using only the HD 1-0 flux, gas masses can be estimated to within a factor of 2 for low mass disks (Mdisk less than 10−3 M⊙). For more massive disks, this uncertainty increases to more than an order of magnitude. Adding the HD 2-1 line or independent information about the vertical structure can reduce this uncertainty to a factor of ~3 for all disk masses. For TW Hya, using the radial and vertical structure from Kama et al. 2016b the observations constrain the gas mass to 6⋅10−3 M⊙ less than Mdisk less than 9⋅10−3 M⊙. Future observations require a 5σ sensitivity of 1.8⋅10−20 W m−2 (2.5⋅10−20 W m−2) and a spectral resolving power R greater than 300 (1000) to detect HD 1-0 (HD 2-1) for all disk masses above 10−5 M⊙ with a line-to-continuum ratio greater than 0.01. These results show that HD can be used as an independent gas mass tracer with a relatively low uncertainty and should be considered as an important science goal for future FIR missions.

Increased H2CO production in the outer disk around HD 163296

Increased H2CO production in the outer disk around HD 163296

Authors:

Hallam et al

Abstract:
It is known that an embedded massive planet will open a gap in a protoplanetary disc via angular momentum exchange with the disc material. The resulting surface density profile of the disc is investigated for one dimensional and two dimensional disc models and, in agreement with previous work, it is found that one dimensional gaps are significantly deeper than their two dimensional counterparts for the same initial conditions. We find, by applying one dimensional torque density distributions to two dimensional discs containing no planet, that the excitement of the Rossby wave instability and the formation of Rossby vortices play a critical role in setting the equilibrium depth of the gap. Being a two dimensional instability, this is absent from one dimensional simulations and does not limit the equilibrium gap depth there. We find similar gap depths between two dimensional gaps formed by torque density distributions, in which the Rossby wave instability is present, and two dimensional planet gaps, in which no Rossby wave instability is present. This can be understood if the planet gap is maintained at marginal stability, even when there is no obvious Rossby wave instability present. Further investigation shows the final equilibrium gap depth is very sensitive to the form of the applied torque density distribution, and using improved one dimensional approximations from three dimensional simulations can go even further to reducing the discrepancy between one and two dimensional models, especially for lower mass planets. This behaviour is found to be consistent across discs with varying parameters.

The Viewing Geometry of Brown Dwarfs Influences Their Observed Colours and Variability Properties

The Viewing Geometry of Brown Dwarfs Influences Their Observed Colours and Variability Properties

Authors:

Vos et al

Abstract:
In this paper we study the full sample of known Spitzer [3.6 μm] and J-band variable brown dwarfs. We calculate the rotational velocities, vsini, of 16 variable brown dwarfs using archival Keck NIRSPEC data and compute the inclination angles of 19 variable brown dwarfs.

The results obtained show that all objects in the sample with mid-IR variability detections are inclined at an angle >20∘, while all objects in the sample displaying J-band variability have an inclination angle >35∘. J-band variability appears to be more affected by inclination than \textit{Spitzer} [3.6 μm] variability, and is strongly attenuated at lower inclinations. Since J-band observations probe deeper into the atmosphere than mid-IR observations, this effect may be due to the increased atmospheric path length of J-band flux at lower inclinations.

We find a statistically significant correlation between the colour anomaly and inclination of our sample, where field objects viewed equator-on appear redder than objects viewed at lower inclinations. Considering the full sample of known variable L, T and Y spectral type objects in the literature, we find that the variability properties of the two bands display notably different trends, due to both intrinsic differences between bands and the sensitivity of ground-based versus space-based searches. However, in both bands we find that variability amplitude may reach a maximum at ∼7−9 hr periods. Finally, we find a strong correlation between colour anomaly and variability amplitude for both the J-band and mid-IR variability detections, where redder objects display higher variability amplitudes.

HD 202206: A Circumbinary Brown Dwarf System

HD 202206: A Circumbinary Brown Dwarf System 

Authors:

Benedict et al

Abstract:
Using Hubble Space Telescope Fine Guidance Sensor astrometry and previously published radial velocity measures, we explore the exoplanetary system HD 202206. Our modeling results in a parallax, ${\pi }_{\mathrm{abs}}=21.96\pm 0.12$ milliseconds of arc, a mass for HD 202206 B of ${{ \mathcal M }}_{B}={0.089}_{-0.006}^{+0.007}\,{{ \mathcal M }}_{\odot }$, and a mass for HD 202206 c of ${{ \mathcal M }}_{c}={17.9}_{-1.8}^{+2.9}\,{{ \mathcal M }}_{\mathrm{Jup}}$. HD 202206 is a nearly face-on G + M binary orbited by a brown dwarf. The system architecture that we determine supports past assertions that stability requires a 5:1 mean motion resonance (we find a period ratio, ${P}_{c}/{P}_{B}=4.92\pm 0.04$) and coplanarity (we find a mutual inclination, ${\rm{\Phi }}=6^\circ \pm 2^\circ $).

A survey for planetary-mass brown dwarfs in the Chamaeleon I star-forming region

A survey for planetary-mass brown dwarfs in the Chamaeleon I star-forming region

Authors:
Esplin et al

Abstract:
We have performed a search for planetary-mass brown dwarfs in the Chamaeleon I star-forming region using proper motions and photometry measured from optical and infrared images from the Spitzer Space Telescope, the Hubble Space Telescope, and ground-based facilities. Through near-infrared spectroscopy at Gemini Observatory, we have confirmed six of the candidates as new late-type members of Chamaeleon I >M7.75. One of these objects, Cha J11110675-7636030, has the faintest extinction-corrected M_K among known members, which corresponds to a mass of 3-6 M_Jup according to evolutionary models. That object and two other new members have redder mid-IR colors than young photospheres at greater than M9.5, which may indicate the presence of disks. However, since those objects may be later than M9.5 and the mid-IR colors of young photospheres are ill-defined at those types, we cannot determine conclusively whether color excesses from disks are present. If Cha J11110675-7636030 does have a disk, it would be a contender for the least-massive known brown dwarf with a disk. Since the new brown dwarfs that we have found extend below our completeness limit of 6-10 M_Jup, deeper observations are needed to measure the minimum mass of the initial mass function in Chamaeleon I.

A feature-rich transmission spectrum for WASP-127b

A feature-rich transmission spectrum for WASP-127b

Authors:

Palle et al

Abstract:

WASP-127b is one of the lowest density planets discovered to date. With a sub-Saturn mass (Mp=0.18±0.02MJ) and super-Jupiter radius (Rp=1.37±0.04RJ), it orbits a bright G5 star, which is about to leave the main-sequence. We aim to explore WASP-127b's atmosphere in order to retrieve its main atmospheric components, and to find hints for its intriguing inflation and evolutionary history. We used the ALFOSC spectrograph at the NOT telescope to observe a low resolution (R∼330, seeing limited) long-slit spectroscopic time series during a planetary transit, and present here the first transmission spectrum for WASP-127b. We find the presence of a strong Rayleigh slope at blue wavelengths and a hint of Na absorption, although the quality of the data does not allow us to claim a detection. At redder wavelengths the absorption features of TiO and VO are the best explanation to fit the data. Although higher signal-to-noise ratio observations are needed to conclusively confirm the absorption features, WASP-127b seems to posses a cloud-free atmosphere and is one of the best targets to perform further characterization studies in the near future.

10 Million Year Old Star PDS 110 has a Hot Jupiter

Periodic Eclipses of the Young Star PDS 110 Discovered with WASP and KELT Photometry

Authors:

Osborn et al

Abstract:
We report the discovery of eclipses by circumstellar disc material associated with the young star PDS 110 in the Ori OB1a association using the SuperWASP and KELT surveys. PDS 110 (HD 290380, IRAS 05209-0107) is a rare Fe/Ge-type star, a ~10 Myr-old accreting intermediate-mass star showing strong infrared excess (LIR/Lbol ~ 0.25). Two extremely similar eclipses with a depth of ~30\% and duration ~25 days were observed in November 2008 and January 2011. We interpret the eclipses as caused by the same structure with an orbital period of 808±2 days. Shearing over a single orbit rules out diffuse dust clumps as the cause, favouring the hypothesis of a companion at ~2AU. The characteristics of the eclipses are consistent with transits by an unseen low-mass (1.8-70MJup) planet or brown dwarf with a circum-secondary disc of diameter ~0.3 AU. The next eclipse event is predicted to take place in September 2017 and could be monitored by amateur and professional observatories across the world.

New Insights on Planet Formation in WASP-47 from a Simultaneous Analysis of Radial Velocities and Transit Timing Variations

New Insights on Planet Formation in WASP-47 from a Simultaneous Analysis of Radial Velocities and Transit Timing Variations 

Authors:

Weiss et al

Abstract:
Measuring precise planet masses, densities, and orbital dynamics in individual planetary systems is an important pathway toward understanding planet formation. The WASP-47 system has an unusual architecture that motivates a complex formation theory. The system includes a hot Jupiter ("b") neighbored by interior ("e") and exterior ("d") sub-Neptunes, and a long-period eccentric giant planet ("c"). We simultaneously modeled transit times from the Kepler K2 mission and 118 radial velocities to determine the precise masses, densities, and Keplerian orbital elements of the WASP-47 planets. Combining RVs and TTVs provides a better estimate of the mass of planet d ($13.6\pm 2.0\,{M}_{\oplus }$) than that obtained with only RVs ($12.75\pm 2.70\,{M}_{\oplus }$) or TTVs ($16.1\pm 3.8\,{M}_{\oplus }$). Planets e and d have high densities for their size, consistent with a history of photoevaporation and/or formation in a volatile-poor environment. Through our RV and TTV analysis, we find that the planetary orbits have eccentricities similar to the solar system planets. The WASP-47 system has three similarities to our own solar system: (1) the planetary orbits are nearly circular and coplanar, (2) the planets are not trapped in mean motion resonances, and (3) the planets have diverse compositions. None of the current single-process exoplanet formation theories adequately reproduce these three characteristics of the WASP-47 system (or our solar system). We propose that WASP-47, like the solar system, formed in two stages: first, the giant planets formed in a gas-rich disk and migrated to their present locations, and second, the high-density sub-Neptunes formed in situ in a gas-poor environment.

An upper limit on the mass of the circumplanetary disk for DH Tau b

An upper limit on the mass of the circumplanetary disk for DH Tau b

Authors:

Wolff et al

Abstract:
DH Tau is a young (∼1 Myr) classical T Tauri star. It is one of the few young PMS stars known to be associated with a planetary mass companion, DH Tau b, orbiting at large separation and detected by direct imaging. DH Tau b is thought to be accreting based on copious Hα emission and exhibits variable Paschen Beta emission. NOEMA observations at 230 GHz allow us to place constraints on the disk dust mass for both DH Tau b and the primary in a regime where the disks will appear optically thin. We estimate a disk dust mass for the primary, DH Tau A of 17.2±1.7M⊕, which gives a disk-to-star mass ratio of 0.014 (assuming the usual Gas-to-Dust mass ratio of 100 in the disk). We find a conservative disk dust mass upper limit of 0.42M⊕ for DH Tau b, assuming that the disk temperature is dominated by irradiation from DH Tau b itself. Given the environment of the circumplanetary disk, variable illumination from the primary or the equilibrium temperature of the surrounding cloud would lead to even lower disk mass estimates. A MCFOST radiative transfer model including heating of the circumplanetary disk by DH Tau b and DH Tau A suggests that a mass averaged disk temperature of 22 K is more realistic, resulting in a dust disk mass upper limit of 0.09M⊕ for DH Tau b. We place DH Tau b in context with similar objects and discuss the consequences for planet formation models.

Internal Structure of Giant and Icy Planets: Importance of Heavy Elements and Mixing

Internal Structure of Giant and Icy Planets: Importance of Heavy Elements and Mixing

Authors: 

Helled et al

Abstract:
In this chapter we summarize current knowledge of the internal structure of giant planets. We concentrate on the importance of heavy elements and their role in determining the planetary composition and internal structure, in planet formation, and during the planetary long-term evolution. We briefly discuss how internal structure models are derived, present the possible structures of the outer planets in the Solar System, and summarise giant planet formation and evolution. Finally, we introduce giant exoplanets and discuss how they can be used to better understand giant planets as a class of planetary objects.

Moderately Eccentric Warm Jupiters from Secular Interactions with Exterior Companions

Moderately Eccentric Warm Jupiters from Secular Interactions with Exterior Companions

Authors:

Anderson et al

Abstract:
Recent work suggests that most warm Jupiters (WJs, giant planets with semi-major axes in the range of 0.1-1 AU) probably form in-situ, or arrive in their observed orbits through disk migration. However, both in-situ formation and disk migration, in their simplest flavors, predict WJs to be in low-eccentricity orbits, in contradiction with many observed WJs that are moderately eccentric (e=0.2−0.7). This paper examines the possibility that the WJ eccentricities are raised by secular interactions with exterior giant planet companions. Eccentricity growth may arise from an inclined companion (through Lidov-Kozai cycles), or from an eccentric, nearly coplanar companion. We quantify the necessary conditions (in terms of the eccentricity, semi-major axis and inclination) for external perturbers of various masses to raise the WJ eccentricity. We also consider the sample of eccentric WJs with detected outer companions, and for each system, identify the range of mutual inclinations needed to generate the observed eccentricity. For most systems, we find that relatively high inclinations (at least ∼40∘) are needed so that Lidov-Kozai cycles are induced; the observed outer companions are typically not sufficiently eccentric to generate the observed WJ eccentricity in a low-inclination configuration. The results of this paper place constraints on possibly unseen external companions to eccentric WJs. Observations that probe mutual inclinations of giant planet systems will help clarify the origin of eccentric WJs and the role of external companions.

Compositional imprints in density-distance-time: a rocky composition for close-in low-mass exoplanets from the location of the valley of evaporation

Compositional imprints in density-distance-time: a rocky composition for close-in low-mass exoplanets from the location of the valley of evaporation

Authors:

Jin et al

Abstract:
We use a theoretical end-to-end model that includes planet formation, thermodynamic evolution, and atmospheric escape to investigate how the statistical imprints of evaporation depend on the bulk composition of the planetary cores (rocky vs. icy). We find that the typical population-wide imprints of evaporation like the location of the "evaporation valley" in the distance-radius plane and the corresponding one-dimensional bimodal distribution in planetary radii are clearly different depending on the bulk composition of close-in low-mass planetary cores. Comparison with the observed position of the valley as found recently by Fulton et al. (2017) suggests that Kepler planets in this domain have a predominately Earth-like rocky composition. Combined with the excess of period ratios outside of MMR, this suggests that low-mass Kepler planets formed inside of the iceline, but still undergoing orbital migration. The core radius becomes visible for planets losing all primordial H/He. For such planets in the "triangle of evaporation" in the distance-radius plane, the degeneracy in possible compositions is reduced. In the observed a-R diagram, we identify a trend to more volatile-rich compositions with increasing planet radius and potentially distance (R/R_earth less than 1.6 rocky; 1.6-3.0 H/He and/or ices; > 3: H/He). Moreover, we find that the mass-density distribution contains important information about planet formation and evolution. Evaporation removes close-in low-mass planets with low density in the mass-density space. This causes density and orbital distance to be anti-correlated for low-mass planets, in contrast to giant planets, where closer planets are less dense, due to inflation mechanisms. The temporal evolution of the statistical properties of the population reported here will be of particular interest for the future PLATO 2.0 mission which will be able to observe the temporal dimension.

K2-66b and K2-106b: Two Extremely Hot Sub-Neptune-size Planets with High Densities

K2-66b and K2-106b: Two Extremely Hot Sub-Neptune-size Planets with High Densities

Authors:

Sinukoff et al

Abstract:

We report precise mass and density measurements of two extremely hot sub-Neptune-size planets from the K2 mission using radial velocities, K2 photometry, and adaptive optics imaging. K2-66 harbors a close-in sub-Neptune-sized (${2.49}_{-0.24}^{+0.34}$ ${R}_{\oplus }$) planet (K2-66b) with a mass of $21.3\pm 3.6$ ${M}_{\oplus }$. Because the star is evolving up the subgiant branch, K2-66b receives a high level of irradiation, roughly twice the main-sequence value. K2-66b may reside within the so-called "photoevaporation desert," a domain of planet size and incident flux that is almost completely devoid of planets. Its mass and radius imply that K2-66b has, at most, a meager envelope fraction (less than 5%) and perhaps no envelope at all, making it one of the largest planets without a significant envelope. K2-106 hosts an ultra-short-period planet (P = 13.7 hr) that is one of the hottest sub-Neptune-size planets discovered to date. Its radius (${1.82}_{-0.14}^{+0.20}$ ${R}_{\oplus }$) and mass ($9.0\pm 1.6$ ${M}_{\oplus }$) are consistent with a rocky composition, as are all other small ultra-short-period planets with well-measured masses. K2-106 also hosts a larger, longer-period planet (${R}_{{\rm{p}}}$ = ${2.77}_{-0.23}^{+0.37}$ ${R}_{\oplus }$, P = 13.3 days) with a mass less than $24.4$ ${M}_{\oplus }$ at 99.7% confidence. K2-66b and K2-106b probe planetary physics in extreme radiation environments. Their high densities reflect the challenge of retaining a substantial gas envelope in such extreme environments.

Water in SuperEarth 55 Cancri e's Atmosphere

A Search for Water in a Super-Earth Atmosphere: High-resolution Optical Spectroscopy of 55Cancri e 

Authors: 

Esteves et al

Abstract:

We present the analysis of high-resolution optical spectra of four transits of 55Cnc e, a low-density super-Earth that orbits a nearby Sun-like star in under 18 hr. The inferred bulk density of the planet implies a substantial envelope, which, according to mass–radius relationships, could be either a low-mass extended or a high-mass compact atmosphere. Our observations investigate the latter scenario, with water as the dominant species. We take advantage of the Doppler cross-correlation technique, high-spectral resolution, and the large wavelength coverage of our observations to search for the signature of thousands of optical water absorption lines. Using our observations with HDS on the Subaru telescope and ESPaDOnS on the Canada–France–Hawaii Telescope, we are able to place a 3σ lower limit of 10 g mol−1 on the mean-molecular weight of 55Cnc e's water-rich (volume mixing ratio >10%), optically thin atmosphere, which corresponds to an atmospheric scale-height of ~80 km. Our study marks the first high-spectral resolution search for water in a super-Earth atmosphere, and demonstrates that it is possible to recover known water-vapor absorption signals in a nearby super-Earth atmosphere, using high-resolution transit spectroscopy with current ground-based instruments.

Habitability Properties of Circumbinary Planets

Habitability Properties of Circumbinary Planets

Author:

Shevchenko

Abstract:
It is shown that several habitability conditions (in fact, at least seven such conditions) appear to be fulfilled automatically by circumbinary planets of main-sequence stars (CBP-MS), whereas on Earth, these conditions are fulfilled only by chance. Therefore, it looks natural that most of the production of replicating biopolymers in the Galaxy is concentrated on particular classes of CBP-MS, and life on Earth is an outlier, in this sense. In this scenario, Lathe's mechanism for the tidal "chain reaction" abiogenesis on Earth is favored as generic for CBP-MS, due to photo-tidal synchronization inherent to them. Problems with this scenario are discussed in detail.

Frequent Flaring in the TRAPPIST-1 System: Unsuited for Life?

Frequent Flaring in the TRAPPIST-1 System—Unsuited for Life?

Authors:

Vida et al

Abstract:
We analyze the K2 light curve of the TRAPPIST-1 system. The Fourier analysis of the data suggests P rot = 3.295 ± 0.003 days. The light curve shows several flares, of which we analyzed 42 events with integrated flare energies of 1.26 × 1030–1.24 × 1033 erg. Approximately 12% of the flares were complex, multi-peaked eruptions. The flaring and the possible rotational modulation shows no obvious correlation. The flaring activity of TRAPPIST-1 probably continuously alters the atmospheres of the orbiting exoplanets, which makes these less favorable for hosting life.

Cosmic Rays near Proxima Centauri b

Cosmic Rays near Proxima Centauri b

Authors:

Struminsky et al

Abstract:

Cosmic rays are an important factor of space weather determining radiation conditions near the Earth and it seems to be essential to clarify radiation conditions near extrasolar planets too. Last year a terrestrial planet candidate was discovered in an orbit around Proxima Centauri. Here we present our estimates on parameters of stellar wind of the Parker model, possible fluxes and fluencies of galactic and stellar cosmic rays based on the available data of the Proxima Centauri activity and its magnetic field. We found that galactic cosmic rays will be practically absent near Proxima~b up to energies of 1~TeV due to the modulation by the stellar wind. Stellar cosmic rays may be accelerated in Proxima Centauri events, which are able to permanently maintain density of stellar cosmic rays in the astrosphere comparable to low energy cosmic ray density in the heliosphere. Maximal proton intensities in extreme Proxima events should be by 3--4 orders more than in solar events.

Hints for Small Disks around Very Low Mass Stars and Brown Dwarfs

Hints for Small Disks around Very Low Mass Stars and Brown Dwarfs

Authors:

Hendler et al

Abstract:

The properties of disks around brown dwarfs and very low mass stars (hereafter VLMOs) provide important boundary conditions on the process of planet formation and inform us about the numbers and masses of planets than can form in this regime. We use the Herschel Space Observatory PACS spectrometer to measure the continuum and [O i] 63 μm line emission toward 11 VLMOs with known disks in the Taurus and Chamaeleon I star-forming regions. We fit radiative transfer models to the spectral energy distributions of these sources. Additionally, we carry out a grid of radiative transfer models run in a regime that connects the luminosity of our sources with brighter T Tauri stars. We find that VLMO disks with sizes 1.3–78 au, smaller than typical T Tauri disks, fit well the spectral energy distributions assuming that disk geometry and dust properties are stellar mass independent. Reducing the disk size increases the disk temperature, and we show that VLMOs do not follow previously derived disk temperature–stellar luminosity relationships if the disk outer radius scales with stellar mass. Only 2 out of 11 sources are detected in [O i] despite a better sensitivity than was achieved for T Tauri stars, suggesting that VLMO disks are underluminous. Using thermochemical models, we show that smaller disks can lead to the unexpected [O i] 63 μm nondetections in our sample. The disk outer radius is an important factor in determining the gas and dust observables. Hence, spatially resolved observations with ALMA—to establish if and how disk radii scale with stellar mass—should be pursued further.

Vertical Distribution and Kinematics of Protoplanetary Nebulae in the Galaxy

Vertical Distribution and Kinematics of Protoplanetary Nebulae in the Galaxy

Authors:

Bobylev et al

Abstract:

The catalogue of protoplanetary nebulae by Vickers et al. has been supplemented with the line-of-sight velocities and proper motions of their central stars from the literature. Based on an exponential density distribution, we have estimated the vertical scale height from objects with an age less than 3 Gyr belonging to the Galactic thin disk (luminosities higher than 5000 Lo) to be h=146+/-15 pc, while from a sample of older objects (luminosities lower than 5000 Lo) it is h=568+/-42 pc. We have produced a list of 147 nebulae in which there are only the line-of-sight velocities for 55 nebulae, only the proper motions for 25 nebulae, and both line-of-sight velocities and proper motions for 67 nebulae. Based on this kinematic sample, we have estimated the Galactic rotation parameters and the residual velocity dispersions of protoplanetary nebulae as a function of their age. We have established that there is a good correlation between the kinematic properties of nebulae and their separation in luminosity proposed by Vickers. Most of the nebulae are shown to be involved in the Galactic rotation, with the circular rotation velocity at the solar distance being V_0=227+/-23 km/s. The following principal semiaxes of the residual velocity dispersion ellipsoid have been found: (sigma1, sigma2, sigma3) = (47, 41, 29) km/s from a sample of young protoplanetary nebulae (with luminosities higher than 5000 Lo), (sigma1, sigma2, sigma3) = (50, 38, 28) km/s from a sample of older protoplanetary nebulae (with luminosities of 4000 Lo or 3500 Lo), and (sigma1, sigma_2, sigma3) = (91, 49, 36) km/s from a sample of halo nebulae (with luminosities of 1700 Lo).

An Analytical Model for the Evolution of the Protoplanetary Disks

An Analytical Model for the Evolution of the Protoplanetary Disks

Authors:
Khajenabi et al

Abstract:
We obtain a new set of analytical solutions for the evolution of a self-gravitating accretion disk by holding the Toomre parameter close to its threshold and obtaining the stress parameter from the cooling rate. In agreement with the previous numerical solutions, furthermore, the accretion rate is assumed to be independent of the disk radius. Extreme situations where the entire disk is either optically thick or optically thin are studied independently, and the obtained solutions can be used for exploring the early or the final phases of a protoplanetary disk evolution. Our solutions exhibit decay of the accretion rate as a power-law function of the age of the system, with exponents −0.75 and −1.04 for optically thick and thin cases, respectively. Our calculations permit us to explore the evolution of the snow line analytically. The location of the snow line in the optically thick regime evolves as a power-law function of time with the exponent −0.16; however, when the disk is optically thin, the location of the snow line as a function of time with the exponent −0.7 has a stronger dependence on time. This means that in an optically thin disk inward migration of the snow line is faster than an optically thick disk.

A Complete ALMA Map of the Fomalhaut Debris Disk

A Complete ALMA Map of the Fomalhaut Debris Disk

Authors:

MacGregor et al

Abstract:

We present ALMA mosaic observations at 1.3 mm (223 GHz) of the Fomalhaut system with a sensitivity of 14 μJy/beam. These observations provide the first millimeter map of the continuum dust emission from the complete outer debris disk with uniform sensitivity, enabling the first conclusive detection of apocenter glow. We adopt a MCMC modeling approach that accounts for the eccentric orbital parameters of a collection of particles within the disk. The outer belt is radially confined with an inner edge of 136.3±0.9 AU and width of 13.5±1.8 AU. We determine a best-fit eccentricity of 0.12±0.01. Assuming a size distribution power law index of q=3.46±0.09, we constrain the dust absorptivity power law index β to be 0.9<β<1.5. The geometry of the disk is robustly constrained with inclination 65.∘6±0.∘3, position angle 337.∘9±0.∘3, and argument of periastron 22.∘5±4.∘3. Our observations do not confirm any of the azimuthal features found in previous imaging studies of the disk with HST, SCUBA, and ALMA. However, we cannot rule out structures ≤10AU in size or which only affect smaller grains. The central star is clearly detected with a flux density of 0.75±0.02 mJy, significantly lower than predicted by current photospheric models. We discuss the implications of these observations for the directly imaged Fomalhaut b and the inner dust belt detected at infrared wavelengths.