- ID:
- ivo://CDS.VizieR/J/ApJ/765/L41
- Title:
- Asteroseismic classification of KIC objects
- Short Name:
- J/ApJ/765/L41
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Of the more than 150000 targets followed by the Kepler Mission, about 10% were selected as red giants. Due to their high scientific value, in particular for Galaxy population studies and stellar structure and evolution, their Kepler light curves were made public in late 2011. More than 13000 (over 85%) of these stars show intrinsic flux variability caused by solar-like oscillations making them ideal for large-scale asteroseismic investigations. We automatically extracted individual frequencies and measured the period spacings of the dipole modes in nearly every red giant. These measurements naturally classify the stars into various populations, such as the red giant branch, the low-mass (M/M_{sun}_<~1.8) helium-core-burning red clump, and the higher-mass (M/M_{sun}_>~1.8) secondary clump. The period spacings also reveal that a large fraction of the stars show rotationally induced frequency splittings. This sample of stars will undoubtedly provide an extremely valuable source for studying the stellar population in the direction of the Kepler field, in particular when combined with complementary spectroscopic surveys.
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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/210/1
- Title:
- Asteroseismic study of solar-type stars
- Short Name:
- J/ApJS/210/1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use asteroseismic data obtained by the NASA Kepler mission to estimate the fundamental properties of more than 500 main-sequence and sub-giant stars. Data obtained during the first 10 months of Kepler science operations were used for this work, when these solar-type targets were observed for one month each in survey mode. Stellar properties have been estimated using two global asteroseismic parameters and complementary photometric and spectroscopic data. Homogeneous sets of effective temperatures, T_eff_, were available for the entire ensemble from complementary photometry; spectroscopic estimates of T_eff_ and [Fe/H] were available from a homogeneous analysis of ground-based data on a subset of 87 stars. We adopt a grid-based analysis, coupling six pipeline codes to 11 stellar evolutionary grids. Through use of these different grid-pipeline combinations we allow implicitly for the impact on the results of stellar model dependencies from commonly used grids, and differences in adopted pipeline methodologies. By using just two global parameters as the seismic inputs we are able to perform a homogeneous analysis of all solar-type stars in the asteroseismic cohort, including many targets for which it would not be possible to provide robust estimates of individual oscillation frequencies (due to a combination of low signal-to-noise ratio and short dataset lengths). The median final quoted uncertainties from consolidation of the grid-based analyses are for the full ensemble (spectroscopic subset) approximately 10.8% (5.4%) in mass, 4.4% (2.2%) in radius, 0.017 dex (0.010 dex) in log g, and 4.3% (2.8%) in mean density. Around 36% (57%) of the stars have final age uncertainties smaller than 1 Gyr. These ages will be useful for ensemble studies, but should be treated carefully on a star-by-star basis. Future analyses using individual oscillation frequencies will offer significant improvements on up to 150 stars, in particular for estimates of the ages, where having the individual frequency data is most important.
- 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/MNRAS/495/2363
- Title:
- Asteroseismology of 36 Kepler subgiants. I.
- Short Name:
- J/MNRAS/495/2363
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The presence of mixed modes makes subgiants excellent targets for asteroseismology, providing a probe for the internal structure of stars. Here we study 36 Kepler subgiants with solar-like oscillations and report their oscillation mode parameters. We performed a so-called peakbagging exercise, i.e. estimating oscillation mode frequencies, linewidths, and amplitudes with a power spectrum model, fitted in the Bayesian framework and sampled with a Markov Chain Monte Carlo algorithm. The uncertainties of the mode frequencies have a median value of 0.180uHz. We obtained seismic parameters from the peakbagging, analysed their correlation with stellar parameters, and examined against scaling relations. The behaviour of seismic parameters (e.g. {Delta}{nu}, {nu}_max_, {epsilon}_p_) is in general consistent with theoretical predictions. We presented the observational p-g diagrams: {gamma}_1_-{Delta}u for early subgiants and {Delta}{Pi}_1_-{Delta}u for late subgiants, and demonstrate their capability to estimate stellar mass. We also found a logg dependence on the linewidths and a mass dependence on the oscillation amplitudes and the widths of oscillation excess. This sample will be valuable constraints for modelling stars and studying mode physics such as excitation and damping.
- ID:
- ivo://CDS.VizieR/J/A+A/580/A27
- Title:
- Asteroseismology of KIC 10526294
- Short Name:
- J/A+A/580/A27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- KIC 10526294 is a very slowly rotating and slowly pulsating late B-type star. Its 19 consecutive dipole gravity modes constitute a series with almost constant period spacing. This unique collection of identified modes probes the near-core environment of this star and holds the potential to reveal the size and structure of the overshooting zone on top of the convective core, as well as the mixing properties of the star. We pursue forward seismic modelling based on adiabatic eigenfrequencies of equilibrium models for eight extensive evolutionary grids tuned to KIC 10526294, by varying the initial mass, metallicity, chemical mixture, and the extent of the overshooting layer on top of the convective core. We examine models for both OP and OPAL opacities and test the occurrence of extra diffusive mixing. We find a tight mass, metallicity relation within the ranges M~3.13 to 3.25M_{sun}_ and Z~0.014 to 0.028. We deduce that an exponentially decaying diffusive core overshooting prescription describes the seismic data better than a step function formulation and derive a value of f_ov between 0.017 and 0.018. Moreover, the inclusion of extra diffusive mixing with a value of log D_mix between 1.75 and 2.00dex (with Dmix in cm^2^/sec) improves the goodness-of-fit based on the observed and modelled frequencies with a factor 11 compared to the case where no extra mixing is considered, irrespective of the (M,Z) combination within the allowed seismic range. The inclusion of diffusive mixing in addition to core overshooting is essential to explain the structure in the observed period spacing pattern of this star. Moreover, we deduce that an exponentially decaying prescription for the core overshooting is to be preferred over a step function. Our best models for KIC 10526294 approach the seismic data to a level that they can serve future inversion of its stellar structure.
- ID:
- ivo://CDS.VizieR/J/MNRAS/463/1297
- Title:
- Asteroseismology of 1523 misclassified red giants
- Short Name:
- J/MNRAS/463/1297
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analysed solar-like oscillations in 1523 Kepler red giants which have previously been misclassified as subgiants, with predicted {nu}_max_ values [based on the Kepler Input Catalogue (KIC)] between 280 and 700{mu}Hz. We report the discovery of 626 new oscillating red giants in our sample, in addition to 897 oscillators that were previously characterized by Hekker et al. from one quarter of Kepler data. Our sample increases the known number of oscillating low-luminosity red giants by 26 per cent (up to >=1900 stars). About three quarters of our sample are classified as ascending red giant branch stars, while the remainder are red-clump stars. A novel scheme was applied to determine {Delta}{nu} for 108 stars with {nu}_max_ close to the Nyquist frequency (387{mu}Hz>{nu}_max_>387{mu}Hz). Additionally, we identified 47 stars oscillating in the super-Nyquist frequency regime, up to 387 {mu}Hz, using long-cadence light curves. We show that the misclassifications are most likely due to large uncertainties in KIC surface gravities, and do not result from the absence of broad-band colours or from different physical properties such as reddening, spatial distribution, mass or metallicity. The sample will be valuable to study oscillations in low-luminosity red giants and to characterize planet candidates around those stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/871/13
- Title:
- Asteroseismology of the WD GD358, 1982-2016
- Short Name:
- J/ApJ/871/13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on the analysis of 34 years of photometric observations of the pulsating helium atmosphere white dwarf GD358. The complete data set includes archival data from 1982 to 2006, and 1195.2hr of new observations from 2007 to 2016. From this data set, we extract 15 frequencies representing g-mode pulsation modes, adding 4 modes to the 11 modes known previously. We present evidence that these 15 modes are l=1 modes, 13 of which belong to a consecutive sequence in radial overtone k. We perform a detailed asteroseismic analysis using models that include parameterized, complex, carbon and oxygen core composition profiles to fit the periods. Recent spectroscopic analyses place GD358 near the red edge of the DBV instability strip, at 24000{+/-}500K and a logg of 7.8{+/-}0.08dex. The surface gravity translates to a mass range of 0.455-0.540M_{sun}_. Our best-fit model has a temperature of 23650K and a mass of 0.5706M_{sun}_. That is slightly more massive than what is suggested by the most recent spectroscopy. We find a pure helium layer mass of 10^-5.50^, consistent with the result of previous studies and the outward diffusion of helium over time.
- ID:
- ivo://CDS.VizieR/J/MNRAS/446/2959
- Title:
- Asterosismology for solar analogues 16 Cyg A/B
- Short Name:
- J/MNRAS/446/2959
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The solar analogues 16 Cyg A and B are excellent asteroseismic targets in the Kepler field of view and together with a red dwarf and a Jovian planet form an interesting system. For these more evolved Sun-like stars we cannot detect surface rotation with the current Kepler data but instead use the technique of asteroseimology to determine rotational properties of both 16 Cyg A and B. We find the rotation periods to be 23.8^1.5^_-1.8_ and 23.2^11.5^_-3.2_ d, and the angles of inclination to be 56^6^_-5_ {deg} and 36^17^_-7_ {deg}, for A and B, respectively. Together with these results we use the published mass and age to suggest that, under the assumption of a solar-like rotation profile, 16 Cyg A could be used when calibrating gyrochronology relations. In addition, we discuss the known 16 Cyg B star-planet eccentricity and measured low obliquity which is consistent with Kozai cycling and tidal theory.
