LHS6343C: A Transiting Field Brown Dwarf Discovered by the Kepler Mission

We report the discovery of a brown dwarf that transits one member of the M+M binary system LHS6343AB every 12.71 days. The transits were discovered using photometric data from the Kelper public data release. The LHS6343 stellar system was previously identified as a single high-proper-motion M dwarf. We use high-contrast imaging to resolve the system into two low-mass stars with masses 0.45 Msun and 0.36 Msun, respectively, and a projected separation of 55 arcsec. High-resolution spectroscopy shows that the more massive component undergoes Doppler variations consistent with Keplerian motion, with a period equal to the transit period and an amplitude consistent with a companion mass of M_C = 62.8 +/- 2.3 Mjup. Based on an analysis of the Kepler light curve we estimate the radius of the companion to be R_C = 0.832 +/- 0.021 Rjup, which is consistent with theoretical predictions of the radius of a > 1 Gyr brown dwarf.Comment: Our previous analysis neglected the dependence of the scaled semimajor axis, a/R, on the transit depth. By not correcting a/R for the third-light contamination, we overestimated the mass of Star A, which led to an overestimate the mass and radius of the LHS6343

Orbital Architectures of Planet-Hosting Binaries:I. Forming Five Small Planets in the Truncated Disk of Kepler-444A

We present the first results from our Keck program investigating the orbital architectures of planet-hosting multiple star systems. Kepler-444 is a metal-poor triple star system that hosts five sub-Earth-sized planets orbiting the primary star (Kepler-444A), as well as a spatially unresolved pair of M dwarfs (Kepler-444BC) at a projected distance of 1.8" (66 AU). We combine our Keck/NIRC2 adaptive optics astrometry with multi-epoch Keck/HIRES RVs of all three stars to determine a precise orbit for the BC pair around A, given their empirically constrained masses. We measure minimal astrometric motion ($1.0\pm0.6$ mas yr$^{-1}$, or $0.17\pm0.10$ km s$^{-1}$), but our RVs reveal significant orbital velocity ($1.7\pm0.2$ km s$^{-1}$) and acceleration ($7.8\pm0.5$ m s$^{-1}$ yr$^{-1}$). We determine a highly eccentric stellar orbit ($e=0.864\pm0.023$) that brings the tight M dwarf pair within $5.0^{+0.9}_{-1.0}$ AU of the planetary system. We validate that the system is dynamically stable in its present configuration via n-body simulations. We find that the A$-$BC orbit and planetary orbits are likely aligned (98%) given that they both have edge-on orbits and misalignment induces precession of the planets out of transit. We conclude that the stars were likely on their current orbits during the epoch of planet formation, truncating the protoplanetary disk at $\approx$2 AU. This truncated disk would have been severely depleted of solid material from which to form the total $\approx$1.5 $M_{\rm Earth}$ of planets. We thereby strongly constrain the efficiency of the conversion of dust into planets and suggest that the Kepler-444 system is consistent with models that explain the formation of more typical close-in Kepler planets in normal, not truncated, disks.Comment: accepted to Ap

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 um 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 PaBeta emission (EW=-11.4 +/- 0.3 A) 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 MJup, 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-sigma) excess at 22 um using WISE photometry.Comment: 25 pages, 13 figures; Accepted by Ap

Direct images and spectroscopy of a giant protoplanet driving spiral arms in MWC 758

Understanding the driving forces behind spiral arms in protoplanetary disks remains a challenge due to the faintness of young giant planets. MWC 758 hosts such a protoplanetary disk with a two-armed spiral pattern that is suggested to be driven by an external giant planet. We present new thermal infrared observations that are uniquely sensitive to redder (i.e., colder or more attenuated) planets than past observations at shorter wavelengths. We detect a giant protoplanet, MWC 758c, at a projected separation of ~100 au from the star. The spectrum of MWC 758c is distinct from the rest of the disk and consistent with emission from a planetary atmosphere with Teff = 500 +/- 100 K for a low level of extinction (AV<30), or a hotter object with a higher level of extinction. Both scenarios are commensurate with the predicted properties of the companion responsible for driving the spiral arms. MWC 758c provides evidence that spiral arms in protoplanetary disks can be caused by cold giant planets or by those whose optical emission is highly attenuated. MWC 758c stands out both as one of the youngest giant planets known, and also as one of the coldest and/or most attenuated. Furthermore, MWC 758c is among the first planets to be observed within a system hosting a protoplanetary disk.Comment: Published in Nature Astronom

Orbit and Dynamical Mass of the Late-T Dwarf Gl 758 B

Gl 758 B is a late-T dwarf orbiting a metal-rich Sun-like star at a projected separation of $\rho$ $\approx$ 1.6" (25 AU). We present four epochs of astrometry of this system with NIRC2 at Keck Observatory spanning 2010 to 2017 together with 630 radial velocities (RVs) of the host star acquired over the past two decades from McDonald Observatory, Keck Observatory, and the Automated Planet Finder at Lick Observatory. The RVs reveal that Gl 758 is accelerating with an evolving rate that varies between 2-5 m s$^{-1}$ yr$^{-1}$, consistent with the expected influence of the imaged companion Gl 758 B. A joint fit of the RVs and astrometry yields a dynamical mass of 42$^{+19}_{-7}$ M$_\mathrm{Jup}$ for the companion with a robust lower limit of 30.5 M$_\mathrm{Jup}$ at the 4-$\sigma$ level. Gl 758 B is on an eccentric orbit ($e$ = 0.26-0.67 at 95% confidence) with a semimajor axis of $a$ = $21.1_{-1.3}^{+2.7}$ AU and an orbital period of $P$ = $96_{-9}^{+21}$ yr, which takes it within $\approx$9 AU from its host star at periastron passage. Substellar evolutionary models generally underpredict the mass of Gl 758 B for nominal ages of 1-6 Gyr that have previously been adopted for the host star. This discrepancy can be reconciled if the system is older---which is consistent with activity indicators and recent isochrone fitting of the host star---or alternatively if the models are systematically overluminous by $\approx$0.1-0.2 dex. Gl 758 B is currently the lowest-mass directly imaged companion inducing a measured acceleration on its host star. In the future, bridging RVs and high-contrast imaging with the next generation of extremely large telescopes and space-based facilities will open the door to the first dynamical mass measurements of imaged exoplanets.Comment: AJ, accepte

The Hawaii Infrared Parallax Program. III. 2MASS J0249-0557 c:A Wide Planetary-mass Companion to a Low-mass Binary in the β Pic Moving Group

We have discovered a wide planetary-mass companion to the $\beta$ Pic moving group member 2MASSJ02495639-0557352 (M6 VL-G) using CFHT/WIRCam astrometry from the Hawaii Infrared Parallax Program. In addition, Keck laser guide star adaptive optics aperture-masking interferometry shows that the host is itself a tight binary. Altogether, 2MASSJ0249-0557ABc is a bound triple system with an $11.6^{+1.0}_{-1.3}$ $M_{\rm Jup}$ object separated by $1950\pm200$ AU (40") from a relatively close ($2.17\pm0.22$ AU, 0.04") pair of $48^{+12}_{-13}$ $M_{\rm Jup}$ and $44^{+11}_{-14}$ $M_{\rm Jup}$ objects. 2MASSJ0249-0557AB is one of the few ultracool binaries to be discovered in a young moving group and the first confirmed in the $\beta$ Pic moving group ($22\pm6$ Myr). The mass, absolute magnitudes, and spectral type of 2MASSJ0249-0557 c (L2 VL-G) are remarkably similar to those of the planet $\beta$ Pic b (L2, $13.0^{+0.4}_{-0.3}$ $M_{\rm Jup}$). We also find that the free-floating object 2MASSJ2208+2921 (L3 VL-G) is another possible $\beta$ Pic moving group member with colors and absolute magnitudes similar to $\beta$ Pic b and 2MASSJ0249-0557 c. $\beta$ Pic b is the first directly imaged planet to have a "twin," namely an object of comparable properties in the same stellar association. Such directly imaged objects provide a unique opportunity to measure atmospheric composition, variability, and rotation across different pathways of assembling planetary-mass objects from the same natal material.Comment: Accepted to AJ, only change is color scheme of figure