89 research outputs found
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
( mas yr, or km s), but our RVs reveal
significant orbital velocity ( km s) and acceleration
( m s yr). We determine a highly eccentric stellar
orbit () that brings the tight M dwarf pair within
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 ABC 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 2 AU. This truncated disk would have been severely depleted of
solid material from which to form the total 1.5 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 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 yr, 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
M for the companion with a robust lower limit of 30.5
M at the 4- level. Gl 758 B is on an eccentric orbit
( = 0.26-0.67 at 95% confidence) with a semimajor axis of =
AU and an orbital period of = yr,
which takes it within 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 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 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
object separated by AU (40")
from a relatively close ( AU, 0.04") pair of
and objects. 2MASSJ0249-0557AB is
one of the few ultracool binaries to be discovered in a young moving group and
the first confirmed in the Pic moving group ( Myr). The mass,
absolute magnitudes, and spectral type of 2MASSJ0249-0557 c (L2 VL-G) are
remarkably similar to those of the planet Pic b (L2,
). We also find that the free-floating object
2MASSJ2208+2921 (L3 VL-G) is another possible Pic moving group member
with colors and absolute magnitudes similar to Pic b and
2MASSJ0249-0557 c. 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
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