- ID:
- ivo://CDS.VizieR/J/ApJ/749/152
- Title:
- Asteroseismic analysis of 22 solar-type stars
- Short Name:
- J/ApJ/749/152
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Asteroseismology with the Kepler space telescope is providing not only an improved characterization of exoplanets and their host stars, but also a new window on stellar structure and evolution for the large sample of solar-type stars in the field. We perform a uniform analysis of 22 of the brightest asteroseismic targets with the highest signal-to-noise ratio observed for 1 month each during the first year of the mission, and we quantify the precision and relative accuracy of asteroseismic determinations of the stellar radius, mass, and age that are possible using various methods. We present the properties of each star in the sample derived from an automated analysis of the individual oscillation frequencies and other observational constraints using the Asteroseismic Modeling Portal (AMP), and we compare them to the results of model-grid-based methods that fit the global oscillation properties. We find that fitting the individual frequencies typically yields asteroseismic radii and masses to ~1% precision, and ages to ~2.5% precision (respectively, 2, 5, and 8 times better than fitting the global oscillation properties). The absolute level of agreement between the results from different approaches is also encouraging, with model-grid-based methods yielding slightly smaller estimates of the radius and mass and slightly older values for the stellar age relative to AMP, which computes a large number of dedicated models for each star. The sample of targets for which this type of analysis is possible will grow as longer data sets are obtained during the remainder of the mission.
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- ID:
- ivo://CDS.VizieR/J/AJ/158/227
- Title:
- Asteroseismic parameters of RGB stars
- Short Name:
- J/AJ/158/227
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Every Sun-like star will eventually evolve into a red giant, a transition which can profoundly affect the evolution of a surrounding planetary system. The timescale of dynamical planet evolution and orbital decay has important implications for planetary habitability, as well as post-main-sequence star and planet interaction, evolution, and internal structure. Here, we investigate these effects by estimating planet occurrence around 2476 low-luminosity red giant branch (LLRGB) stars observed by the NASA K2 mission. We measure stellar masses and radii using asteroseismology, with median random uncertainties of 3.7% in mass and 2.2% in radius. We compare this planet population to the known population of planets around dwarf Sun-like stars, accounting for detection efficiency differences between the stellar populations. We find that 0.49%+/-0.28% of LLRGB stars host planets larger than Jupiter with orbital periods less than 10 days, tentatively higher than main-sequence stars hosting similar planets (0.15%+/-0.06%). Our results suggest that the effects of stellar evolution on the occurrence of close-in planets larger than Jupiter are not significant until stars have begun ascending substantially up the red giant branch (>~5-6 R_{sun}_).
- ID:
- ivo://CDS.VizieR/J/ApJ/767/127
- Title:
- Asteroseismic solutions for 77 Kepler stars
- Short Name:
- J/ApJ/767/127
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used asteroseismology to determine fundamental properties for 66 Kepler planet-candidate host stars, with typical uncertainties of 3% and 7% in radius and mass, respectively. The results include new asteroseismic solutions for four host stars with confirmed planets (Kepler-4, Kepler-14, Kepler-23 and Kepler-25) and increase the total number of Kepler host stars with asteroseismic solutions to 77. A comparison with stellar properties in the planet-candidate catalog by Batalha et al. (2013, J/ApJS/204/24) shows that radii for subgiants and giants obtained from spectroscopic follow-up are systematically too low by up to a factor of 1.5, while the properties for unevolved stars are in good agreement. We furthermore apply asteroseismology to confirm that a large majority of cool main-sequence hosts are indeed dwarfs and not misclassified giants. Using the revised stellar properties, we recalculate the radii for 107 planet candidates in our sample, and comment on candidates for which the radii change from a previously giant-planet/brown-dwarf/stellar regime to a sub-Jupiter size or vice versa. A comparison of stellar densities from asteroseismology with densities derived from transit models in Batalha et al. assuming circular orbits shows significant disagreement for more than half of the sample due to systematics in the modeled impact parameters or due to planet candidates that may be in eccentric orbits. Finally, we investigate tentative correlations between host-star masses and planet-candidate radii, orbital periods, and multiplicity, but caution that these results may be influenced by the small sample size and detection biases.
- ID:
- ivo://CDS.VizieR/J/ApJS/236/42
- Title:
- Asteroseismology of ~16000 Kepler red giants
- Short Name:
- J/ApJS/236/42
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- 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 16094 oscillating red giants, using end-of-mission long-cadence data. We produced a homogeneous catalog of the frequency of maximum power (typical uncertainty {sigma}_{nu}max_=1.6% ), the mean large frequency separation ({sigma}_{Delta}{nu}_=0.6%), oscillation amplitude ({sigma}_A_=4.7%), granulation power ({sigma}_gran_=8.6% ), power excess width ({sigma}_width_=8.8%), seismically derived stellar mass ({sigma}_M_=7.8%), radius ({sigma}_R_=2.9% ), and thus surface gravity ({sigma}_logg_=0.01dex). 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 {nu}_max_, which might hold clues for understanding the excitation and damping mechanisms of the oscillation modes. We find that 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 0.5dex. 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.
- ID:
- ivo://CDS.VizieR/J/ApJS/219/33
- Title:
- BANYAN. VII. Candidate YMG members from BASS
- Short Name:
- J/ApJS/219/33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a near-infrared (NIR) spectroscopic follow-up survey of 182 M4-L7 low-mass stars and brown dwarfs (BDs) from the BANYAN All-Sky Survey (BASS) for candidate members of nearby, young moving groups (YMGs). We confirm signs of low gravity for 42 new BD discoveries with estimated masses between 8 and 75M_Jup_ and identify previously unrecognized signs of low gravity for 24 known BDs. We refine the fraction of low-gravity dwarfs in the high-probability BASS sample to ~82%. We use this unique sample of 66 young BDs, supplemented with 22 young BDs from the literature, to construct new empirical NIR absolute magnitude and color sequences for low-gravity BDs. We show that low-resolution NIR spectroscopy alone cannot differentiate between the ages of YMGs younger than ~120Myr, and that the BT-Settl atmosphere models do not reproduce well the dust clouds in field or low-gravity L-type dwarfs. We obtain a spectroscopic confirmation of low gravity for 2MASS J14252798-3650229, which is a new ~27M_Jup_, L4 {gamma} bona fide member of AB Doradus. We identify a total of 19 new low-gravity candidate members of YMGs with estimated masses below 13M_Jup_, 7 of which have kinematically estimated distances within 40pc. These objects will be valuable benchmarks for a detailed atmospheric characterization of planetary-mass objects with the next generation of instruments. We find 16 strong candidate members of the Tucana-Horologium association with estimated masses between 12.5 and 14M_Jup_, a regime where our study was particularly sensitive. This would indicate that for this association there is at least one isolated object in this mass range for every 17.5_-5.0_^+6.6^ main-sequence stellar member, a number significantly higher than expected based on standard log-normal initial mass function, however, in the absence of radial velocity and parallax measurements for all of them, it is likely that this over-density is caused by a number of young interlopers from other associations.
- ID:
- ivo://CDS.VizieR/J/A+A/630/A135
- Title:
- Beyond the exoplanet mass-radius relation
- Short Name:
- J/A+A/630/A135
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The mass and radius are two fundamental properties to characterize exoplanets but only for a relatively small fraction of exoplanets are they both available. The mass is often derived from radial velocity measurements while the radius is almost always measured with the transit method. For a large number of exoplanets, either the radius or the mass is unknown, while the host star has been characterized. Several mass-radius relations dependent on the planet's type have been published which often allow to predict the radius, as well as a bayesian code which forecasts the radius of an exoplanet given the mass or vice versa. Our goal is to derive the radius of exoplanets using only observables extracted from spectra used primarily to determine radial velocities and spectral parameters. Our objective is to obtain a mass-radius relation that is independent of the planet's type. We work with a database of confirmed exoplanets with known radii and masses as well as the planets from our Solar System. Using random forests, a machine learning algorithm, we compute the radius of exoplanets and compare the results to the published radii. Our code, BEM, is available online. On top of this, we also explore how the radius estimates compare to previously published mass-radius relations. The estimated radii reproduces the spread in radius found for high mass planets better than previous mass-radius relations. The average error on the radius is 1.8R_Earth_ across the whole range of radii from 1 to 22R_Earth_. We found that a random forest algorithm is able to derive reliable radii especially for planets between 4 and 20R_Earth_, for which the error is smaller than 25%. The algorithm has a low bias but still a high variance, which could be reduced by limiting the growth of the forest or adding more data. The random forest algorithm is a promising method to derive exoplanet properties. We show that the exoplanet's mass and equilibrium temperature are the relevant properties which constrain the radius, and do it with higher accuracy than the previous methods.
- ID:
- ivo://CDS.VizieR/J/ApJS/244/43
- Title:
- Binary stars parameters from LAMOST & Kepler obs.
- Short Name:
- J/ApJS/244/43
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The parameter distribution of binaries is a fundamental knowledge of the stellar systems. A statistical study on the binary stars is carried out based on the LAMOST spectral and Kepler photometric database. We presented a catalog of 1320 binary stars with plentiful parameters, including period, binary subtype, atmosphere parameters (Teff, [Fe/H], and logg), and the physical properties, such as mass, radius, and age, for the primary component stars. Based on this catalog, the unbiased distribution, rather than the observed distribution, was obtained after the correction of selection biases by the Monte Carlo method considering comprehensive affecting factors. For the first time, the orbital eccentricity distribution of the detached binaries is presented. The distribution differences between the three subtypes of binaries (detached, semidetached, and contact) are demonstrated, which can be explained by the generally accepted evolutional scenarios. Many characteristics of the binary stars, such as huge mass transfer on semidetached binaries, period cutoff on contact binaries, period-temperature relationship of contact binaries, and the evolved binaries, are reviewed by the new database. This work supports a common evolutionary scenario for all subtypes of binary stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/794/35
- Title:
- Binary white dwarfs atmospheric parameters
- Short Name:
- J/ApJ/794/35
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed spectroscopic analysis of 61 low-mass white dwarfs and provide precise atmospheric parameters, masses, and updated binary system parameters based on our new model atmosphere grids and the most recent evolutionary model calculations. For the first time, we measure systematic abundances of He, Ca, and Mg for metal-rich, extremely low mass white dwarfs and examine the distribution of these abundances as a function of effective temperature and mass. Based on our preliminary results, we discuss the possibility that shell flashes may be responsible for the presence of the observed He and metals. We compare stellar radii derived from our spectroscopic analysis to model-independent measurements and find good agreement except for white dwarfs with T_eff_<~10000 K. We also calculate the expected gravitational wave strain for each system and discuss their significance to the eLISA space-borne gravitational wave observatory. Finally, we provide an update on the instability strip of extremely low mass white dwarf pulsators.
- ID:
- ivo://CDS.VizieR/J/AJ/153/16
- Title:
- Calibrator stars catalog for interferometers
- Short Name:
- J/AJ/153/16
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Benchmark stars with known angular diameters are key to calibrating interferometric observations. With the advent of optical interferometry, there is a need for suitably bright, well-vetted calibrator stars over a large portion of the sky. We present a catalog of uniformly computed angular diameters for 1510 stars in the northern hemisphere, brighter than V=6 and with declinations -15{deg}<delta<82{deg}. The median angular stellar diameter is 0.529 mas. The list has been carefully cleansed of all known binary and multiple stellar systems. We derive the angular diameters for each of the stars by fitting spectral templates to the observed spectral energy distributions (SEDs) from literature fluxes. We compare these derived angular diameters against those measured by optical interferometry for 75 of the stars, as well as to 176 diameter estimates from previous calibrator catalogs, finding in general excellent agreement. The final catalog includes our goodness-of-fit metrics as well as an online atlas of our SED fits. The catalog presented here permits selection of the best calibrator stars for current and future visible-light interferometric observations.
- ID:
- ivo://CDS.VizieR/J/A+A/433/1155
- Title:
- Calibrator stars for 200m baseline interferometry
- Short Name:
- J/A+A/433/1155
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of reference stars suitable for calibrating infrared interferometric observations. In the K band, visibilities can be calibrated with a precision of 1% on baselines up to 200 meters for the whole sky, and up to 300 meters for some part of the sky. This work, extending to longer baselines a previous catalog compiled by Borde et al. (2002, Cat. <J/A+A/393/183>), is particularly well adapted to hectometric-class interferometers. We use the absolute spectro-photometric calibration method introduced by Cohen et al. (1999AJ....117.1864C) to derive the angular diameters of our new set of stars.
