93 research outputs found
KOI-3890: A high mass-ratio asteroseismic red-giantM-dwarf eclipsing binary undergoing heartbeat tidal interactions
KOI-3890 is a highly eccentric, 153-day period eclipsing, single-lined
spectroscopic binary system containing a red-giant star showing solar-like
oscillations alongside tidal interactions. The combination of transit
photometry, radial velocity observations, and asteroseismology have enabled the
detailed characterisation of both the red-giant primary and the M-dwarf
companion, along with the tidal interaction and the geometry of the system. The
stellar parameters of the red-giant primary are determined through the use of
asteroseismology and grid-based modelling to give a mass and radius of
and
respectively. When combined with
transit photometry the M-dwarf companion is found to have a mass and radius of
and
. Moreover, through
asteroseismology we constrain the age of the system through the red-giant
primary to be . This provides a constraint on
the age of the M-dwarf secondary, which is difficult to do for other M-dwarf
binary systems. In addition, the asteroseismic analysis yields an estimate of
the inclination angle of the rotation axis of the red-giant star of
degrees. The obliquity of the system\textemdash the
angle between the stellar rotation axis and the angle normal to the orbital
plane\textemdash is also derived to give degrees
showing that the system is consistent with alignment. We observe no radius
inflation in the M-dwarf companion when compared to current low-mass stellar
models.Comment: 11 pages, 5 figures, accepted for publication in MNRA
Bayesian hierarchical inference of asteroseismic inclination angles
The stellar inclination angle-the angle between the rotation axis of a star
and our line of sight-provides valuable information in many different areas,
from the characterisation of the geometry of exoplanetary and eclipsing binary
systems, to the formation and evolution of those systems. We propose a method
based on asteroseismology and a Bayesian hierarchical scheme for extracting the
inclination angle of a single star. This hierarchical method therefore provides
a means to both accurately and robustly extract inclination angles from red
giant stars. We successfully apply this technique to an artificial dataset with
an underlying isotropic inclination angle distribution to verify the method. We
also apply this technique to 123 red giant stars observed with
. We also show the need for a selection function to account
for possible population-level biases, that are not present in individual
star-by-star cases, in order to extend the hierarchical method towards
inferring underlying population inclination angle distributions.Comment: 20 pages, 12 figures, accepted for publication in MNRA
Synergy between asteroseismology and exoplanet science:an outlook
Space-based asteroseismology has been playing an important role in the
characterization of exoplanet-host stars and their planetary systems. The
future looks even brighter, with space missions such as NASA's TESS and ESA's
PLATO ready to take on this legacy. In this contribution, we provide an outlook
on the synergy between asteroseismology and exoplanet science, namely, on the
prospect of conducting a populational study of giant planets around oscillating
evolved stars with the TESS mission.Comment: 8 pages, 11 figures, 1 table; To appear in the Proceedings of PHOST
"Physics of Oscillating Stars" - a conference in honour of Prof. H.
Shibahashi, 2-7 Sep 2018, Banyuls-sur-mer, France; Edited by J. Ballot, S.
Vauclair and G. Vauclai
Kepler-432: a red giant interacting with one of its two long period giant planets
We report the discovery of Kepler-432b, a giant planet ()
transiting an evolved star with an orbital period of days. Radial velocities (RVs) reveal that
Kepler-432b orbits its parent star with an eccentricity of , which we also measure independently with
asterodensity profiling (AP; ), thereby confirming
the validity of AP on this particular evolved star. The well-determined
planetary properties and unusually large mass also make this planet an
important benchmark for theoretical models of super-Jupiter formation.
Long-term RV monitoring detected the presence of a non-transiting outer planet
(Kepler-432c; days), and adaptive optics imaging revealed a nearby
(0\farcs87), faint companion (Kepler-432B) that is a physically bound M dwarf.
The host star exhibits high signal-to-noise asteroseismic oscillations, which
enable precise measurements of the stellar mass, radius and age. Analysis of
the rotational splitting of the oscillation modes additionally reveals the
stellar spin axis to be nearly edge-on, which suggests that the stellar spin is
likely well-aligned with the orbit of the transiting planet. Despite its long
period, the obliquity of the 52.5-day orbit may have been shaped by star-planet
interaction in a manner similar to hot Jupiter systems, and we present
observational and theoretical evidence to support this scenario. Finally, as a
short-period outlier among giant planets orbiting giant stars, study of
Kepler-432b may help explain the distribution of massive planets orbiting giant
stars interior to 1 AU.Comment: 22 pages, 19 figures, 5 tables. Accepted to ApJ on Jan 24, 2015
(submitted Nov 11, 2014). Updated with minor changes to match published
versio
Three years of Fermi GBM Earth Occultation Monitoring: Observations of Hard X-ray/Soft Gamma-Ray Sources
The Gamma ray Burst Monitor (GBM) on board Fermi has been providing
continuous data to the astronomical community since 2008 August 12. In this
paper we present the results of the analysis of the first three years of these
continuous data using the Earth occultation technique to monitor a catalog of
209 sources. From this catalog, we detect 99 sources, including 40 low-mass
X-ray binary/neutron star systems, 31 high-mass X-ray binary neutron star
systems, 12 black hole binaries, 12 active galaxies, 2 other sources, plus the
Crab Nebula, and the Sun. Nine of these sources are detected in the 100-300 keV
band, including seven black-hole binaries, the active galaxy Cen A, and the
Crab. The Crab and Cyg X-1 are also detected in the 300-500 keV band. GBM
provides complementary data to other sky-monitors below 100 keV and is the only
all-sky monitor above 100 keV. Up-to-date light curves for all of the catalog
sources can be found at http://heastro.phys.lsu.edu/gbm/.Comment: 24 pages, 12 figures, accepted for publication in ApJ
The masses of retired A stars with asteroseismology::Kepler and K2 observations of exoplanet hosts
We investigate the masses of "retired A stars" using asteroseismic detections
on seven low-luminosity red-giant and sub-giant stars observed by the NASA
Kepler and K2 Missions. Our aim is to explore whether masses derived from
spectroscopy and isochrone fitting may have been systematically overestimated.
Our targets have all previously been subject to long term radial velocity
observations to detect orbiting bodies, and satisfy the criteria used by
Johnson et al. (2006) to select survey stars that may have had A-type (or early
F-type) main-sequence progenitors. The sample actually spans a somewhat wider
range in mass, from up to . Whilst for five of the seven stars the reported discovery mass from
spectroscopy exceeds the mass estimated using asteroseismology, there is no
strong evidence for a significant, systematic bias across the sample. Moreover,
comparisons with other masses from the literature show that the absolute scale
of any differences is highly sensitive to the chosen reference literature mass,
with the scatter between different literature masses significantly larger than
reported error bars. We find that any mass difference can be explained through
use of differing constraints during the recovery process. We also conclude that
underestimated uncertainties on the input parameters can significantly bias the
recovered stellar masses, which may have contributed to the controversy on the
mass scale for retired A stars.Comment: Accepted MNRAS, 14 pages, 7 Figures, 3 Table
TESS asteroseismology of the known red-giant host stars HD 212771 and HD 203949
International audienc
Revisiting the Red Giant Branch Hosts KOI-3886 and ι Draconis.:Detailed Asteroseismic Modeling and Consolidated Stellar Parameters
Asteroseismology is playing an increasingly important role in the characterization of red giant host stars and their planetary systems. Here, we conduct detailed asteroseismic modeling of the evolved red giant branch (RGB) hosts KOI-3886 and ι Draconis, making use of end-of-mission Kepler (KOI-3886) and multisector TESS (ι Draconis) time-series photometry. We also model the benchmark star KIC 8410637, a member of an eclipsing binary, thus providing a direct test to the seismic determination. We test the impact of adopting different sets of observed modes as seismic constraints. Inclusion of .,"= 1 and 2 modes improves the precision of the stellar parameters, albeit marginally, compared to adopting radial modes alone, with 1.9%-3.0% (radius), 5%-9% (mass), and 19%-25% (age) reached when using all p-dominated modes as constraints. Given the very small spacing of adjacent dipole mixed modes in evolved RGB stars, the sparse set of observed g-dominated modes is not able to provide extra constraints, further leading to highly multimodal posteriors. Access to multiyear time-series photometry does not improve matters, with detailed modeling of evolved RGB stars based on (lower-resolution) TESS data sets attaining a precision commensurate with that based on end-of-mission Kepler data. Furthermore, we test the impact of varying the atmospheric boundary condition in our stellar models. We find the mass and radius estimates to be insensitive to the description of the near-surface layers, at the expense of substantially changing both the near-surface structure of the best-fitting models and the values of associated parameters like the initial helium abundance, Y i . Attempts to measure Y i from seismic modeling of red giants may thus be systematically dependent on the choice of atmospheric physics
AIMS - A new tool for stellar parameter determinations using asteroseismic constraints
A key aspect in the determination of stellar properties is the comparison of
observational constraints with predictions from stellar models. Asteroseismic
Inference on a Massive Scale (AIMS) is an open source code that uses Bayesian
statistics and a Markov Chain Monte Carlo approach to find a representative set
of models that reproduce a given set of classical and asteroseismic
constraints. These models are obtained by interpolation on a pre-calculated
grid, thereby increasing computational efficiency. We test the accuracy of the
different operational modes within AIMS for grids of stellar models computed
with the Li\`ege stellar evolution code (main sequence and red giants) and
compare the results to those from another asteroseismic analysis pipeline,
PARAM. Moreover, using artificial inputs generated from models within the grid
(assuming the models to be correct), we focus on the impact on the precision of
the code when considering different combinations of observational constraints
(individual mode frequencies, period spacings, parallaxes, photospheric
constraints,...). Our tests show the absolute limitations of precision on
parameter inferences using synthetic data with AIMS, and the consistency of the
code with expected parameter uncertainty distributions. Interpolation testing
highlights the significance of the underlying physics to the analysis
performance of AIMS and provides caution as to the upper limits in parameter
step size. All tests demonstrate the flexibility and capability of AIMS as an
analysis tool and its potential to perform accurate ensemble analysis with
current and future asteroseismic data yields.Comment: Accepted for publication in MNRAS. 17 pages, 17 figure
The Occurrence of Rocky Habitable-zone Planets around Solar-like Stars from Kepler Data
We present the occurrence rates for rocky planets in the habitable zones (HZs) of main-sequence dwarf stars based on the Kepler DR25 planet candidate catalog and Gaia-based stellar properties. We provide the first analysis in terms of star-dependent instellation flux, which allows us to track HZ planets. We define η⊕ as the HZ occurrence of planets with radii between 0.5 and 1.5 R⊕ orbiting stars with effective temperatures between 4800 and 6300 K. We find that η⊕ for the conservative HZ is between 0.37^(+0.48)_(−0.21) (errors reflect 68% credible intervals) and 0.60^(+0.90)_(−0.36) planets per star, while the optimistic HZ occurrence is between 0.58^(+0.73)_(−0.33) and 0.88^(+1.28)_(−0.51) planets per star. These bounds reflect two extreme assumptions about the extrapolation of completeness beyond orbital periods where DR25 completeness data are available. The large uncertainties are due to the small number of detected small HZ planets. We find similar occurrence rates between using Poisson likelihood Bayesian analysis and using Approximate Bayesian Computation. Our results are corrected for catalog completeness and reliability. Both completeness and the planet occurrence rate are dependent on stellar effective temperature. We also present occurrence rates for various stellar populations and planet size ranges. We estimate with 95% confidence that, on average, the nearest HZ planet around G and K dwarfs is ~6 pc away and there are ~4 HZ rocky planets around G and K dwarfs within 10 pc of the Sun
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