Brendan P. Bowler

NEAR-INFRARED SPECTROSCOPY OF THE EXTRASOLAR PLANET HR 8799 b*

We present 2.12-2.23 ?m high contrast integral field spectroscopy of the extrasolar planet HR?8799 b. Our observations were obtained with OSIRIS on the Keck II telescope and sample the 2.2 ?m CH4 feature, which is useful for spectral classification and as a temperature diagnostic for ultracool objects. The spectrum of HR?8799 b is relatively featureless, with little or no methane absorption, and does not exhibit the strong CH4 seen in T dwarfs of similar absolute magnitudes. The spectrum is consistent with field objects from early-L to T4 (3? confidence level), with a best-fitting type of T2. A similar analysis of the published 1-4 ?m photometry shows the infrared spectral energy distribution (SED) matches L5-L8 field dwarfs, especially the reddest known objects which are believed to be young and/or very dusty. Overall, we find that HR?8799 b has a spectral type consistent with L5-T2, although its SED is atypical compared to most field objects. We fit the 2.2 ?m spectrum and the infrared SED using the Hubeny & Burrows, Burrows et?al., and Ames-Dusty model atmosphere grids, which incorporate non-equilibrium chemistry, non-solar metallicities, and clear and cloudy variants. No models agree with all of the data, but those with intermediate clouds produce significantly better fits. The largest discrepancy occurs in the J band, which is highly suppressed in HR?8799 b. Models with high eddy diffusion coefficients and high metallicities are somewhat preferred over those with equilibrium chemistry and solar metallicity. The best-fitting effective temperatures range from 1300 to 1700?K with radii between ~0.3 and 0.5 R Jup. These values are inconsistent with evolutionary model-derived values of 800-900?K and 1.1-1.3 R Jup based on the luminosity of HR?8799 b and the age of HR?8799, a discrepancy that probably results from imperfect atmospheric models or the limited range of physical parameters covered by the models. The low temperature inferred from evolutionary models indicates that HR?8799 b is ~400?K cooler than field L/T transition objects, providing further evidence that the L/T transition is gravity-dependent. With an unusually dusty photosphere, an exceptionally low luminosity for its spectral type, and hints of extreme secondary physical parameters, HR?8799 b appears to be unlike any class of field brown dwarf currently known.

RETIRED A STARS AND THEIR COMPANIONS. III. COMPARING THE MASS-PERIOD DISTRIBUTIONS OF PLANETS AROUND A-TYPE STARS AND SUN-LIKE STARS

We present an analysis of ~5 years of Lick Observatory radial velocity measurements targeting a uniform sample of 31 intermediate-mass (IM) subgiants (1.5 ≾ M_*/M_☉ ≾ 2.0) with the goal of measuring the occurrence rate of Jovian planets around (evolved) A-type stars and comparing the distributions of their orbital and physical characteristics to those of planets around Sun-like stars. We provide updated orbital solutions incorporating new radial velocity measurements for five known planet-hosting stars in our sample; uncertainties in the fitted parameters are assessed using a Markov-Chain Monte Carlo method. The frequency of Jovian planets interior to 3 AU is 26^(+9)_(–8)%, which is significantly higher than the 5%-10% frequency observed around solar-mass stars. The median detection threshold for our sample includes minimum masses down to {0.2, 0.3, 0.5, 0.6, 1.3} M_(Jup) within {0.1, 0.3, 0.6, 1.0, 3.0} AU. To compare the properties of planets around IM stars to those around solar-mass stars we synthesize a population of planets based on the parametric relationship dN ∝ M^α P^β dlnMdlnP, the observed planet frequency, and the detection limits we derived. We find that the values of α and β for planets around solar-type stars from Cumming et al. fail to reproduce the observed properties of planets in our sample at the 4σ level, even when accounting for the different planet occurrence rates. Thus, the properties of planets around A stars are markedly different than those around Sun-like stars, suggesting that only a small (~50%) increase in stellar mass has a large influence on the formation and orbital evolution of planets.

Retired A Stars and Their Companions. VII. 18 New Jovian Planets

We report the detection of 18 Jovian planets discovered as part of our Doppler survey of subgiant stars at Keck Observatory, with follow-up Doppler and photometric observations made at McDonald and Fairborn Observatories, respectively. The host stars have masses 0.927 ≤ M_*/M_☉ ≤ 1.95, radii 2.5 ≤ R_*/R_☉ ≤ 8.7, and metallicities –0.46 ≤ [Fe/H] ≤+0.30. The planets have minimum masses 0.9 M_Jup ≤ M_P sin i ≲ 13 M_Jup and semimajor axes a ≥ 0.76 AU. These detections represent a 50% increase in the number of planets known to orbit stars more massive than 1.5 M_☉ and provide valuable additional information about the properties of planets around stars more massive than the Sun.

A Disk around the Planetary-mass Companion GSC?06214-00210?b: Clues about the Formation of Gas Giants on Wide Orbits

We present Keck OSIRIS 1.1-1.8 ?m adaptive optics integral field spectroscopy of the planetary-mass companion to GSC 06214-00210, a member of the ~5?Myr Upper Scorpius OB association. We infer a spectral type of L0 ? 1, and our spectrum exhibits multiple signs of youth. The most notable feature is exceptionally strong Pa? emission (EW = ?11.4 ? 0.3 ?), which signals the presence of a circumplanetary accretion disk. The luminosity of GSC?06214-00210?b combined with its age yields a model-dependent mass of 14 ? 2 M Jup, making it the lowest-mass companion to show evidence of a disk. With a projected separation of 320?AU, the formation of GSC?06214-00210?b and other very low mass companions on similarly wide orbits is unclear. One proposed mechanism is formation at close separations followed by planet-planet scattering to much larger orbits. Since that scenario involves a close encounter with another massive body, which is probably destructive to circumplanetary disks, it is unlikely that GSC?06214-00210?b underwent a scattering event in the past. This implies that planet-planet scattering is not solely responsible for the population of gas giants on wide orbits. More generally, the identification of disks around young planetary companions on wide orbits offers a novel method to constrain the formation pathway of these objects, which is otherwise notoriously difficult to do for individual systems. We also refine the spectral type of the primary from M1 to K7 and detect a mild (2?) excess at 22 ?m using Wide-Field Infrared Survey Explorer photometry.

Characterizing K2 Planet Discoveries: A Super-Earth Transiting the Bright K Dwarf HIP 116454

We report the first planet discovery from the two-wheeled Kepler (K2) mission: HIP 116454 b. The host star HIP 116454 is a bright (V = 10.1, K = 8.0) K1 dwarf with high proper motion and a parallax-based distance of 55.2 ± 5.4 pc. Based on high-resolution optical spectroscopy, we find that the host star is metal-poor with (Fe/H) =− 0.16 ± 0.08 and has a radius R� = 0.716 ± 0.024 Rand mass M� = 0.775 ± 0.027 M� . The star was observed by the Kepler spacecraft during its Two-Wheeled Concept Engineering Test in 2014 February. During the 9 days of observations, K2 observed a single transit event. Using a new K2 photometric analysis technique, we are able to correct small telescope drifts and recover the observed transit at high confidence, corresponding to a planetary radius of Rp = 2.53 ± 0.18 R⊕. Radial velocity observations with the HARPS-N spectrograph reveal a 11.82 ± 1.33 M⊕ planet in a 9.1 day orbit, consistent with the transit depth, duration, and ephemeris. Follow-up photometric measurements from the MOST satellite confirm the transit observed in the K2 photometry and provide a refined ephemeris, making HIP 116454 b amenable for future follow-up observations of this latest addition to the growing population of transiting super-Earths around nearby, bright stars.

Imaging Extrasolar Giant Planets

High-contrast adaptive optics imaging is a powerful technique to probe the architectures of planetary systems from the outside-in and survey the atmospheres of self-luminous giant planets. Direct imaging has rapidly matured over the past decade and especially the last few years with the advent of high-order adaptive optics systems, dedicated planet-finding instruments with specialized coronagraphs, and innovative observing and post-processing strategies to suppress speckle noise. This review summarizes recent progress in high-contrast imaging with particular emphasis on observational results, discoveries near and below the deuterium-burning limit, and a practical overview of large-scale surveys and dedicated instruments. I conclude with a statistical meta-analysis of deep imaging surveys in the literature. Based on observations of 384 unique and single young (

Retired A Stars and Their Companions. VI. A Pair of Interacting Exoplanet Pairs Around the Subgiants 24 Sextanis and HD?200964

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Retired A Stars and Their Companions. IV. Seven Jovian Exoplanets from Keck Observatory

5--300~Myr) stars spanning stellar masses between 0.1--3.0~\Msun, the overall occurrence rate of 5--13~\Mjup \ companions at orbital distances of 30--300~AU is 0.6

STELLAR AND PLANETARY PROPERTIES OF K2 CAMPAIGN 1 CANDIDATES AND VALIDATION OF 17 PLANETS, INCLUDING A PLANET RECEIVING EARTH-LIKE INSOLATION

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A Search for High Proper Motion T Dwarfs with Pan-STARRS1 + 2MASS + WISE

\% assuming hot-start evolutionary models. The most massive giant planets regularly accessible to direct imaging are about as rare as hot Jupiters are around Sun-like stars. Dividing this sample into individual stellar mass bins does not reveal any statistically-significant trend in planet frequency with host mass: giant planets are found around 2.8