120 research outputs found
Mixed-mode Ensemble Asteroseismology of Low-Luminosity Kepler Red Giants
We present measurements of the dipole mode asymptotic period spacing
(), the coupling factor between p- and g- modes (), the g-mode
phase offset (), and the mixed-mode frequency rotational splitting
() for 1,074 low-luminosity red giants from the
Kepler mission. Using oscillation mode frequencies extracted from each star, we
apply Bayesian optimization to estimate from the power spectrum
of the stretched period spectrum and to perform the subsequent forward
modelling of the mixed-mode frequencies. With our measurements, we show that
the mode coupling factor shows significant anti-correlation with both
stellar mass and metallicity, and can reveal highly metal-poor stars. We
present the evolution of up the lower giant branch up to before
the luminosity bump, and find no significant trends in or
with stellar mass and metallicity in our sample.
Additionally, we identify six new red giants showing anomalous distortions in
their g-mode pattern. Our data products, code, and results are provided in a
public repository.Comment: Accepted in the Astrophysical Journal. Code repository is at
https://github.com/jsk389/BOChaMM and associated peakbagging data is publicly
available at https://zenodo.org/record/788863
Asteroseismology of 16000 Kepler Red Giants: Global Oscillation Parameters, Masses, and Radii
The Kepler mission has provided exquisite data to perform an ensemble
asteroseismic analysis on evolved stars. In this work we systematically
characterize solar-like oscillations and granulation for 16,094 oscillating red
giants, using end-of-mission long-cadence data. We produced a homogeneous
catalog of the frequency of maximum power (typical uncertainty
=1.6\%), the mean large frequency separation
(=0.6\%), oscillation amplitude (=4.7\%),
granulation power (=8.6\%), power excess width (=8.8\%), seismically-derived stellar mass (=7.8\%),
radius (=2.9\%), and thus surface gravity (=0.01 dex). Thanks to the large red giant sample, we confirm that
red-giant-branch (RGB) and helium-core-burning (HeB) stars collectively differ
in the distribution of oscillation amplitude, granulation power, and width of
power excess, which is mainly due to the mass difference. The distribution of
oscillation amplitudes shows an extremely sharp upper edge at fixed , which might hold clues to understand the excitation and damping
mechanisms of the oscillation modes. We find both oscillation amplitude and
granulation power depend on metallicity, causing a spread of 15\% in
oscillation amplitudes and a spread of 25\% in granulation power from
[Fe/H]=-0.7 to 0.5 dex. Our asteroseismic stellar properties can be used as
reliable distance indicators and age proxies for mapping and dating galactic
stellar populations observed by Kepler. They will also provide an excellent
opportunity to test asteroseismology using Gaia parallaxes, and lift
degeneracies in deriving atmospheric parameters in large spectroscopic surveys
such as APOGEE and LAMOST.Comment: Accepted for publication in ApJS. Both table 1 and 2 are available
for download as ancillary file
HD-TESS: An Asteroseismic Catalog of Bright Red Giants within TESS Continuous Viewing Zones
We present HD-TESS, a catalog of 1,709 bright () red giants from
the Henry Draper (HD) Catalog with asteroseismic measurements based on
photometry from NASA's Transiting Exoplanet Survey Satellite (TESS). Using
light curves spanning at least six months across a single TESS observing cycle,
we provide measurements of global asteroseismic parameters
( and ) and evolutionary state for each star in
the catalog. We adopt literature values of atmospheric stellar parameters to
estimate the masses and radii of the giants in our catalog using asteroseismic
scaling relations, and observe that HD-TESS giants on average have larger
masses compared to Kepler red giants. Additionally, we present the discovery of
oscillations in 99 red giants in astrometric binary systems, including those
with subdwarf or white dwarf companions. Finally, we benchmark radii from
asteroseismic scaling relations against those measured using long-baseline
interferometry for 18 red giants and find that correction factors to the
scaling relations improve the agreement between asteroseismic and
interferometric radii to approximately 3%.Comment: 20 pages, 12 figures. Accepted for publication in the Astronomical
Journal. Table of asteroseismic masses and radii is available as an ancillary
fil
A Unified Exploration of the Chronology of the Galaxy
The Milky Way has distinct structural stellar components linked to its
formation and subsequent evolution, but disentangling them is nontrivial. With
the recent availability of high-quality data for a large numbers of stars in
the Milky Way, it is a natural next step for research in the evolution of the
Galaxy to perform automated explorations with unsupervised methods of the
structures hidden in the combination of large-scale spectroscopic, astrometric,
and asteroseismic data sets. We determine precise stellar properties for 21,076
red giants, mainly spanning 2-15 kpc in Galactocentric radii, making it the
largest sample of red giants with measured asteroseismic ages available to
date. We explore the nature of different stellar structures in the Galactic
disc by using Gaussian mixture models as an unsupervised clustering method to
find substructure in the combined chemical, kinematic, and age subspace. The
best-fit mixture model yields four distinct physical Galactic components in the
stellar disc: the thin disc, the kinematically heated thin disc, the thick
disc, and the stellar halo. We find hints of an age asymmetry between the
Northern and Southern hemisphere and we measure the vertical and radial age
gradient of the Galactic disc using the asteroseismic ages extended to further
distances than previous studies.Comment: 18 pages, 12 figures, accepted for publication in MNRA
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