1,549 research outputs found
Orbital Parameter Determination for Wide Stellar Binary Systems in the Age of Gaia
The orbits of binary stars and planets, particularly eccentricities and
inclinations, encode the angular momentum within these systems. Within stellar
multiple systems, the magnitude and (mis)alignment of angular momentum vectors
among stars, disks, and planets probes the complex dynamical processes guiding
their formation and evolution. The accuracy of the \textit{Gaia} catalog can be
exploited to enable comparison of binary orbits with known planet or disk
inclinations without costly long-term astrometric campaigns. We show that
\textit{Gaia} astrometry can place meaningful limits on orbital elements in
cases with reliable astrometry, and discuss metrics for assessing the
reliability of \textit{Gaia} DR2 solutions for orbit fitting. We demonstrate
our method by determining orbital elements for three systems (DS Tuc AB, GK/GI
Tau, and Kepler-25/KOI-1803) using \textit{Gaia} astrometry alone. We show that
DS Tuc AB's orbit is nearly aligned with the orbit of DS Tuc Ab, GK/GI Tau's
orbit might be misaligned with their respective protoplanetary disks, and the
Kepler-25/KOI-1803 orbit is not aligned with either component's transiting
planetary system. We also demonstrate cases where \textit{Gaia} astrometry
alone fails to provide useful constraints on orbital elements. To enable
broader application of this technique, we introduce the python tool
\texttt{lofti\_gaiaDR2} to allow users to easily determine orbital element
posteriors.Comment: 18 pages, 10 figures, accepted for publication in Ap
The gold standard: accurate stellar and planetary parameters for eight Kepler M dwarf systems enabled by parallaxes
We report parallaxes and proper motions from the Hawaii Infrared Parallax Program for eight nearby M dwarf stars with transiting exoplanets discovered by Kepler. We combine our directly measured distances with mass-luminosity and radiusâluminosity relationships to significantly improve constraints on the host starsâ properties. Our astrometry enables the identification of wide stellar companions to the planet hosts. Within our limited sample, all the multi-transiting planet hosts (three of three) appear to be single stars, while nearly all (four of five) of the systems with a single detected planet have wide stellar companions. By applying strict priors on average stellar density from our updated radius and mass in our transit fitting analysis, we measure the eccentricity probability distributions for each transiting planet. Planets in single-star systems tend to have smaller eccentricities than those in binaries, although this difference is not significant in our small sample. In the case of Kepler-42bcd, where the eccentricities are known to be â0, we demonstrate that such systems can serve as powerful tests of M dwarf evolutionary models by working in Lâ â Ïâ space. The transit-fit density for Kepler- 42bcd is inconsistent with model predictions at 2.1Ï (22%), but matches more empirical estimates at 0.2Ï (2%), consistent with earlier results showing model radii of M dwarfs are underinflated. Gaia will provide high-precision parallaxes for the entire Kepler M dwarf sample, and TESS will identify more planets transiting nearby, late-type stars, enabling significant improvements in our understanding of the eccentricity distribution of small planets and the parameters of late-type dwarfs.Support for Program number HST-HF2-51364.001-A was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555.Some of the data presented in this paper were obtained from the Mikulski Archive for Space Telescopes (MAST). STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NNX09AF08G and by other grants and contracts. This paper includes data collected by the Kepler mission. Funding for the Kepler mission is provided by the NASA Science Mission directorate. The authors acknowledge the Texas Advanced Computing Center (TACC) at The University of Texas at Austin for providing HPC resources that have contributed to the research results reported within this paper. URL: http://www.tacc.utexas.edu. (HST-HF2-51364.001-A - NASA through Space Telescope Science Institute; NAS5-26555 - NASA; NNX09AF08G - NASA Office of Space Science; NASA Science Mission directorate
Boyajian's Star B::The co-moving stellar companion to KIC 8462852 A
The light curve of KIC 8462852, a.k.a Boyajian's Star, undergoes deep dips
the origin of which remains unclear. A faint star 2\arcsec to the east
was discovered in Keck/NIRC2 imaging in Boyajian et al. (2016), but its status
as a binary, and possible contribution to the observed variability, was
unclear. Here, we use three epochs of Keck/NIRC2 imaging, spanning five years,
in JHK near-infrared bands to obtain 1-mas precision astrometry. We show that
the two objects exhibit common proper motion, measure a relative velocity of
mas yr ( km s) and conclude
that they are a binary pair at AU projected separation. There is
marginal detection of possible orbital motion, but our astrometry is
insufficient to characterize the orbit. We show that two other point sources
are not associated with KIC 8462852. We recommend that attempts to model KIC
8462852 A's light curve should revisit the possibility that the bound stellar
companion may play a role in causing the irregular brightness variations, for
example through disruption of the orbits of bodies around the primary due to
long-term orbital evolution of the binary orbit.Comment: 11 pages, 7 figures, 2 tables Accepted for publication in Ap
The Impact of Stellar Multiplicity on Planetary Systems, I.:The Ruinous Influence of Close Binary Companions
The dynamical influence of binary companions is expected to profoundly influence planetary systems. However, the difficulty of identifying planets in binary systems has left the magnitude of this effect uncertain; despite numerous theoretical hurdles to their formation and survival, at least some binary systems clearly host planets. We present high-resolution imaging of 382 Kepler Objects of Interest (KOIs) obtained using adaptive-optics imaging and nonredundant aperture-mask interferometry on the Keck II telescope. Among the full sample of 506 candidate binary companions to KOIs, we super-resolve some binary systems to projected separations of 0.4; we instead only found 23 companions (a 4.6Ï deficit), many of which must be wider pairs that are only close in projection. When the binary population is parametrized with a semimajor axis cutoff a cut and a suppression factor inside that cutoff S bin, we find with correlated uncertainties that inside au, the planet occurrence rate in binary systems is only times that of wider binaries or single stars. Our results demonstrate that a fifth of all solar-type stars in the Milky Way are disallowed from hosting planetary systems due to the influence of a binary companion
HIP 38939B: A New Benchmark T Dwarf in the Galactic Plane Discovered with Pan-STARRS1
We report the discovery of a wide brown dwarf companion to the mildly
metal-poor ([Fe/H]=-0.24), low galactic latitude (b = 1.88 deg) K4V star HIP
38939. The companion was discovered by its common proper motion with the
primary and its red optical (Pan-STARRS1) and blue infrared (2MASS) colors. It
has a projected separation of 1630 AU and a near-infrared spectral type of
T4.5. As such it is one of only three known companions to a main sequence star
which have early/mid-T spectral types (the others being HN Peg B and eps Indi
B). Using chromospheric activity we estimate an age for the primary of
900{+1900,-600} Myr. This value is also in agreement with the age derived from
the star's weak ROSAT detection. Comparison with evolutionary models for this
age range indicates that HIP 38939B falls in the mass range 38+/-20 Mjup with
an effective temperature range of 1090+/-60 K. Fitting our spectrum with
atmospheric models gives a best fitting temperature of 1100 K. We include our
object in an analysis of the population of benchmark T dwarfs and find that
while older atmospheric models appeared to over-predict the temperature of the
coolest objects compared to evolutionary models, more recent atmospheric models
provide better agreement.Comment: ApJ, in press. Tiny changes incorporated into final version: added
analysis of likelihood of companionship, clarified the fitting proceedure,
and updated the benchmark analysis to highlight when the quoted evolutionary
models use the atmospheric model they are being compared to as a boundary
conditio
Testing the models: NIR imaging and spectroscopy of the benchmark T-dwarf binary Eps Indi B
The relative roles of metallicity and surface gravity on the near-infrared
spectra of late-T brown dwarfs are not yet fully understood, and evolutionary
models still need to be calibrated in order to provide accurate estimates of
brown dwarf physical parameters from measured spectra. The T-type brown dwarfs
Eps Indi Ba and Bb forming the tightly bound binary Eps Indi B, which orbits
the K4V star Eps Indi A, are nowadays the only such benchmark T dwarfs for
which all important physical parameters such as metallicity, age and mass are
(or soon will be) known. We present spatially resolved VLT/NACO images and low
resolution spectra of Eps Indi B in the J, H and K near-infrared bands. The
spectral types of Eps Indi Ba and Bb are determined by direct comparison of the
flux-calibrated JHK spectra with T dwarf standard template spectra and also by
NIR spectral indices. Eps Indi Bb is confirmed as a T6 while the spectral type
of Eps Indi Ba is T1.5 so somewhat later than the previously reported T1.
Constrained values for surface gravity and effective temperature are derived by
comparison with model spectra. The evolutionary models predict masses around
about 53 M_J for Eps Indi Ba and about 34 M_J for Eps Indi Bb, slightly higher
than previously reported values. The suppressed J-band and enhanced K-band flux
of Eps Indi Ba indicates that a noticeable cloud layer is still present in a
T1.5 dwarf while no clouds are needed to model the spectrum of Eps Indi Bb.Comment: 7 pages, 5 figures, accepted by Ap
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