542 research outputs found
The APOKASC Catalog: An Asteroseismic and Spectroscopic Joint Survey of Targets in the Kepler Fields
We present the first APOKASC catalog of spectroscopic and asteroseismic
properties of 1916 red giants observed in the Kepler fields. The spectroscopic
parameters provided from the Apache Point Observatory Galactic Evolution
Experiment project are complemented with asteroseismic surface gravities,
masses, radii, and mean densities determined by members of the Kepler
Asteroseismology Science Consortium. We assess both random and systematic
sources of error and include a discussion of sample selection for giants in the
Kepler fields. Total uncertainties in the main catalog properties are of order
80 K in Teff , 0.06 dex in [M/H], 0.014 dex in log g, and 12% and 5% in mass
and radius, respectively; these reflect a combination of systematic and random
errors. Asteroseismic surface gravities are substantially more precise and
accurate than spectroscopic ones, and we find good agreement between their mean
values and the calibrated spectroscopic surface gravities. There are, however,
systematic underlying trends with Teff and log g. Our effective temperature
scale is between 0-200 K cooler than that expected from the Infrared Flux
Method, depending on the adopted extinction map, which provides evidence for a
lower value on average than that inferred for the Kepler Input Catalog (KIC).
We find a reasonable correspondence between the photometric KIC and
spectroscopic APOKASC metallicity scales, with increased dispersion in KIC
metallicities as the absolute metal abundance decreases, and offsets in Teff
and log g consistent with those derived in the literature. We present mean
fitting relations between APOKASC and KIC observables and discuss future
prospects, strengths, and limitations of the catalog data.Comment: 49 pages. ApJSupp, in press. Full machine-readable ascii files
available under ancillary data. Categories: Kepler targets, asteroseismology,
large spectroscopic survey
They are Small Worlds After All: Revised Properties of Kepler M Dwarf Stars and their Planets
We classified the reddest () stars observed by the NASA
mission into main sequence dwarf or evolved giant stars and determined the
properties of 4216 M dwarfs based on a comparison of available photometry with
that of nearby calibrator stars, as well as available proper motions and
spectra. We revised the properties of candidate transiting planets using the
stellar parameters, high-resolution imaging to identify companion stars, and,
in the case of binaries, fitting light curves to identify the likely planet
host. In 49 of 54 systems we validated the primary as the host star. We
inferred the intrinsic distribution of M dwarf planets using the method of
iterative Monte Carlo simulation. We compared several models of planet orbital
geometry and clustering and found that one where planets are exponentially
distributed and almost precisely coplanar best describes the distribution of
multi-planet systems. We determined that M dwarfs host an average of
planets with radii of 1-4 and orbital periods of
1.5-180 d. The radius distribution peaks at and is
essentially zero at , although we identify three giant planet
candidates other than the previously confirmed Kepler-45b. There is suggestive
but not significant evidence that the radius distribution varies with orbital
period. The distribution with logarithmic orbital period is flat except for a
decline for orbits less than a few days. Twelve candidate planets, including
two Jupiter-size objects, experience an irradiance below the threshold level
for a runaway greenhouse on an Earth-like planet and are thus in a "habitable
zone".Comment: MNRAS, in press. Tables 1, 3, and 4 are available in electronic form
in the "anc" director
Characterizing two solar-type Kepler subgiants with asteroseismology: KIC10920273 and KIC11395018
Determining fundamental properties of stars through stellar modeling has
improved substantially due to recent advances in asteroseismology. Thanks to
the unprecedented data quality obtained by space missions, particularly CoRoT
and Kepler, invaluable information is extracted from the high-precision stellar
oscillation frequencies, which provide very strong constraints on possible
stellar models for a given set of classical observations. In this work, we have
characterized two relatively faint stars, KIC10920273 and KIC11395018, using
oscillation data from Kepler photometry and atmospheric constraints from
ground-based spectroscopy. Both stars have very similar atmospheric properties;
however, using the individual frequencies extracted from the Kepler data, we
have determined quite distinct global properties, with increased precision
compared to that of earlier results. We found that both stars have left the
main sequence and characterized them as follows: KIC10920273 is a
one-solar-mass star (M=1.00 +/- 0.04 M_sun), but much older than our Sun
(t=7.12 +/- 0.47 Gyr), while KIC11395018 is significantly more massive than the
Sun (M=1.27 +/- 0.04 M_sun) with an age close to that of the Sun (t=4.57 +/-
0.23 Gyr). We confirm that the high lithium abundance reported for these stars
should not be considered to represent young ages, as we precisely determined
them to be evolved subgiants. We discuss the use of surface lithium abundance,
rotation and activity relations as potential age diagnostics.Comment: 12 pages, 3 figures, 5 tables. Accepted by Ap
Automated preparation of Kepler time series of planet hosts for asteroseismic analysis
One of the tasks of the Kepler Asteroseismic Science Operations Center
(KASOC) is to provide asteroseismic analyses on Kepler Objects of Interest
(KOIs). However, asteroseismic analysis of planetary host stars presents some
unique complications with respect to data preprocessing, compared to pure
asteroseismic targets. If not accounted for, the presence of planetary transits
in the photometric time series often greatly complicates or even hinders these
asteroseismic analyses. This drives the need for specialised methods of
preprocessing data to make them suitable for asteroseismic analysis. In this
paper we present the KASOC Filter, which is used to automatically prepare data
from the Kepler/K2 mission for asteroseismic analyses of solar-like planet host
stars. The methods are very effective at removing unwanted signals of both
instrumental and planetary origins and produce significantly cleaner
photometric time series than the original data. The methods are automated and
can therefore easily be applied to a large number of stars. The application of
the filter is not restricted to planetary hosts, but can be applied to any
solar-like or red giant stars observed by Kepler/K2.Comment: Accepted for publication in MNRA
Verifying asteroseismically determined parameters of Kepler stars using hipparcos parallaxes: self-consistent stellar properties and distances
Accurately determining the properties of stars is of prime importance for
characterizing stellar populations in our Galaxy. The field of asteroseismology
has been thought to be particularly successful in such an endeavor for stars in
different evolutionary stages. However, to fully exploit its potential, robust
methods for estimating stellar parameters are required and independent
verification of the results is mandatory. With this purpose, we present a new
technique to obtain stellar properties by coupling asteroseismic analysis with
the InfraRed Flux Method. By using two global seismic observables and
multi-band photometry, the technique allows us to obtain masses, radii,
effective temperatures, bolometric fluxes, and hence distances for field stars
in a self-consistent manner. We apply our method to 22 solar-like oscillators
in the Kepler short-cadence sample, that have accurate Hipparcos parallaxes.
Our distance determinations agree to better than 5%, while measurements of
spectroscopic effective temperatures and interferometric radii also validate
our results. We briefly discuss the potential of our technique for stellar
population analysis and models of Galactic Chemical Evolution.Comment: 28 pages, 5 figures, ApJ, accepte
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