- ID:
- ivo://CDS.VizieR/J/A+A/616/A94
- Title:
- KIC red giants radial modes amplitude & lifetime
- Short Name:
- J/A+A/616/A94
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The space-borne missions CoRoT and Kepler have provided photometric observations of unprecedented quality. The study of solar-like oscillations observed in red giant stars by these satellites allows a better understanding of the different physical processes occurring in their interiors. In particular, the study of the mode excitation and damping is a promising way to improve our understanding of stellar physics that has, so far, been performed only on a limited number of targets. The recent asteroseismic characterization of the evolutionary status for a large number of red giants allows us to study the physical processes acting in the interior of red giants and how they are modified during stellar evolution. In this work, we aim to obtain information on the excitation and damping of pressure modes through the measurement of the stars' pressure mode widths and amplitudes and to analyze how they are modified with stellar evolution. The objective is to bring observational constraints on the modeling of the physical processes behind mode excitation and damping. We fit the frequency spectra of red giants with well-defined evolutionary status using Lorentzian functions to derive the pressure mode widths and amplitudes. To strengthen our conclusions, we used two different fitting techniques. Pressure mode widths and amplitudes were determined for more than 5000 red giants. With a stellar sample two orders of magnitude larger than previous results, we confirmed that the mode width depends on stellar evolution and varies with stellar effective temperature. In addition, we discovered that the mode width depends on stellar mass. We also confirmed observationally the influence of the stellar metallicity on the mode amplitudes, as predicted by models.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/844/102
- Title:
- KIC star parallaxes from asteroseismology vs Gaia
- Short Name:
- J/ApJ/844/102
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a comparison of parallaxes and radii from asteroseismology and Gaia DR1 (TGAS) for 2200 Kepler stars spanning from the main sequence to the red-giant branch. We show that previously identified offsets between TGAS parallaxes and distances derived from asteroseismology and eclipsing binaries have likely been overestimated for parallaxes <~5-10mas (~90%-98% of the TGAS sample). The observed differences in our sample can furthermore be partially compensated by adopting a hotter Teff scale (such as the infrared flux method) instead of spectroscopic temperatures for dwarfs and subgiants. Residual systematic differences are at the ~2% level in parallax across three orders of magnitude. We use TGAS parallaxes to empirically demonstrate that asteroseismic radii are accurate to ~5% or better for stars between ~0.8-8R_{sun}_. We find no significant offset for main- sequence (<~1.5R_{sun}_) and low-luminosity RGB stars (~3-8R_{sun}_), but seismic radii appear to be systematically underestimated by ~5% for subgiants (~1.5-3R_{sun}_). We find no systematic errors as a function of metallicity between [Fe/H]~-0.8 to +0.4dex, and show tentative evidence that corrections to the scaling relation for the large frequency separation ({Delta}{nu}) improve the agreement with TGAS for RGB stars. Finally, we demonstrate that beyond ~3kpc asteroseismology will provide more precise distances than end-of-mission Gaia data, highlighting the synergy and complementary nature of Gaia and asteroseismology for studying galactic stellar populations.
- ID:
- ivo://CDS.VizieR/J/A+A/543/A54
- Title:
- 61 main-sequence and subgiant oscillations
- Short Name:
- J/A+A/543/A54
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Solar-like oscillations have been observed by Kepler and CoRoT in several solar-type stars, thereby providing a way to probe the stars using asteroseismology We provide the mode frequencies of the oscillations of various stars required to perform a comparison with those obtained from stellar modelling. We used a time series of nine months of data for each star. The 61 stars observed were categorised in three groups: simple, F-like, and mixed-mode. The simple group includes stars for which the identification of the mode degree is obvious. The F-like group includes stars for which the identification of the degree is ambiguous. The mixed-mode group includes evolved stars for which the modes do not follow the asymptotic relation of low-degree frequencies. Following this categorisation, the power spectra of the 61 main-sequence and subgiant stars were analysed using both maximum likelihood estimators and Bayesian estimators, providing individual mode characteristics such as frequencies, linewidths, and mode heights. We developed and describe a methodology for extracting a single set of mode frequencies from multiple sets derived by different methods and individual scientists. We report on how one can assess the quality of the fitted parameters using the likelihood ratio test and the posterior probabilities. We provide the mode frequencies of 61 stars (with their 1-{sigma} error bars), as well as their associated echelle diagrams.
- ID:
- ivo://CDS.VizieR/J/AJ/160/18
- Title:
- M giant stars asteroseismology with Kepler and APOGEE
- Short Name:
- J/AJ/160/18
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Evolved stars near the tip of the red giant branch show solar-like oscillations with periods spanning hours to months and amplitudes ranging from ~1mmag to ~100mmag. The systematic detection of the resulting photometric variations with ground-based telescopes would enable the application of asteroseismology to a much larger and more distant sample of stars than is currently accessible with space-based telescopes such as Kepler or the ongoing Transiting Exoplanet Survey Satellite mission. We present an asteroseismic analysis of 493 M giants using data from two ground-based surveys: the Asteroid Terrestrial-impact Last Alert System (ATLAS) and the All-Sky Automated Survey for Supernovae (ASAS-SN). By comparing the extracted frequencies with constraints from Kepler, the Sloan Digital Sky Survey Apache Point Observatory Galaxy Evolution Experiment, and Gaia we demonstrate that ground-based transient surveys allow accurate distance measurements to oscillating M giants with a precision of ~15%. Using stellar population synthesis models we predict that ATLAS and ASAS-SN can provide asteroseismic distances to ~2x106 galactic M giants out to typical distances of 20-50kpc, vastly improving the reach of Gaia and providing critical constraints for Galactic archeology and galactic dynamics.
- ID:
- ivo://CDS.VizieR/J/A+A/619/A116
- Title:
- New variables and 2 delta Scuti pulsations
- Short Name:
- J/A+A/619/A116
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Dome C in Antarctica is a promising site for photometric observations thanks to the continuous night during the Antarctic winter and favorable weather conditions. We developed instruments to assess the quality of this site for photometry in the visible and to detect and characterize variable objects through the Antarctic Search for Transiting ExoPlanets (ASTEP) project. Here, we present the full analysis of four winters of data collected with ASTEP South, a 10cm refractor pointing continuously toward the celestial south pole. We achieved nearly continuous observations over the winters. We improved the instrument over the years and developed specific data reduction methods. We measure an average sky background of 20mag/arcsec^2^ in the 579-642nm bandpass. We built the lightcurves of 6000 stars and developed a model to infer the photometric quality of Dome C from the lightcurves themselves. The weather is photometric 67.1+/-4.2% of the time and veiled 21.8+/-2.0% of the time. The remaining time corresponds to poor quality data or winter storms.We analyzed the lightcurves of Oct and HD 184465 and find that the amplitude of their main frequency varies by a factor of 3.5 and 6.7 over the four years, respectively. We also identify 34 new variable stars and eight new eclipsing binaries with periods ranging from 0.17 to 81 days. The phase coverage that we achieved with ASTEP South is exceptional for a ground-based instrument and the data quality enables the detection and study of variable objects. These results demonstrate the high quality of Dome C for photometry in the visible and for time series observations in general.
- ID:
- ivo://CDS.VizieR/J/A+A/640/A36
- Title:
- OB stars TESS phot. & high-resolution spectroscopy
- Short Name:
- J/A+A/640/A36
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Massive stars are predicted to excite internal gravity waves (IGWs) by turbulent core convection and from turbulent pressure fluctuations in their near-surface layers. These IGWs are extremely efficient at transporting angular momentum and chemical species within stellar interiors, but they remain largely unconstrained observationally. We aim to characterise the photometric detection of IGWs across a large number of O and early-B stars in the Hertzsprung-Russell diagram, and explain the ubiquitous detection of stochastic variability in the photospheres of massive stars. We combined high-precision time-series photometry from the NASA Transiting Exoplanet Survey Satellite with high-resolution ground-based spectroscopy of 70 stars with spectral types O and B to probe the relationship between the photometric signatures of IGWs and parameters such as spectroscopic mass, luminosity, and macroturbulence. A relationship is found between the location of a star in the spectroscopic Hertzsprung-Russell diagram and the amplitudes and frequencies of stochastic photometric variability in the light curves of massive stars. Furthermore, the properties of the stochastic variability are statistically correlated with macroturbulent velocity broadening in the spectral lines of massive stars. The common ensemble morphology for the stochastic low-frequency variability detected in space photometry and its relationship to macroturbulence is strong evidence for IGWs in massive stars, since these types of waves are unique in providing the dominant tangential velocity field required to explain the observed spectroscopy.
- ID:
- ivo://CDS.VizieR/J/ApJ/889/L34
- Title:
- Oscillations in red giants from TESS data
- Short Name:
- J/ApJ/889/L34
- Date:
- 17 Jan 2022 00:14:58
- Publisher:
- CDS
- Description:
- Since the onset of the "space revolution" of high-precision high-cadence photometry, asteroseismology has been demonstrated as a powerful tool for informing Galactic archeology investigations. The launch of the NASA Transiting Exoplanet Survey Satellite (TESS) mission has enabled seismic-based inferences to go full sky-providing a clear advantage for large ensemble studies of the different Milky Way components. Here we demonstrate its potential for investigating the Galaxy by carrying out the first asteroseismic ensemble study of red giant stars observed by TESS. We use a sample of 25 stars for which we measure their global asteroseimic observables and estimate their fundamental stellar properties, such as radius, mass, and age. Significant improvements are seen in the uncertainties of our estimates when combining seismic observables from TESS with astrometric measurements from the Gaia mission compared to when the seismology and astrometry are applied separately. Specifically, when combined we show that stellar radii can be determined to a precision of a few percent, masses to 5%-10%, and ages to the 20% level. This is comparable to the precision typically obtained using end-of-mission Kepler data.
- ID:
- ivo://CDS.VizieR/J/ApJ/858/L7
- Title:
- Red clump stars selected from LAMOST and APOGEE
- Short Name:
- J/ApJ/858/L7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Core helium-burning red clump (RC) stars are excellent standard candles in the Milky Way. These stars may have more precise distance estimates from spectrophotometry than from Gaia parallaxes beyond 3kpc. However, RC stars have values of Teff and logg that are very similar to some red giant branch (RGB) stars. Especially for low-resolution spectroscopic studies where Teff, logg, and [Fe/H] can only be estimated with limited precision, separating RC stars from RGB through established methods can incur ~20% contamination. Recently, Hawkins+ (2018ApJ...853...20H) demonstrated that the additional information in single-epoch spectra, such as the C/N ratio, can be exploited to cleanly differentiate RC and RGB stars. In this second paper of the series, we establish a data-driven mapping from spectral flux space to independently determined asteroseismic parameters, the frequency and the period spacing. From this, we identify 210371 RC stars from the publicly available LAMOST DR3 and APOGEE DR14 data, with ~9% of contamination. We provide an RC sample of 92249 stars with a contamination of only ~3%, by restricting the combined analysis to LAMOST stars with S/N_pix_>=75. This demonstrates that high-signal-to-noise ratio (S/N), low-resolution spectra covering a broad wavelength range can identify RC samples at least as pristine as their high- resolution counterparts. As coming and ongoing surveys such as TESS, DESI, and LAMOST will continue to improve the overlapping training spectroscopic-asteroseismic sample, the method presented in this study provides an efficient and straightforward way to derive a vast yet pristine sample of RC stars to reveal the three-dimensional (3D) structure of the Milky Way.
- ID:
- ivo://CDS.VizieR/J/MNRAS/466/3344
- Title:
- Red-giant stars classification
- Short Name:
- J/MNRAS/466/3344
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Determining the ages of red-giant stars is a key problem in stellar astrophysics. One of the difficulties in this determination is to know the evolutionary state of the individual stars - i.e. have they started to burn Helium in their cores? That is the topic of this paper. Asteroseismic data provide a route to achieving this information. What we present here is a highly autonomous way of determining the evolutionary state from an analysis of the power spectrum of the light curve. The method is fast and efficient and can provide results for a large number of stars. It uses the structure of the dipole-mode oscillations, which have a mixed character in red-giant stars, to determine some measures that are used in the categorization. It does not require that all the individual components of any given mode be separately characterized. Some 6604 red-giant stars have been classified. Of these, 3566 are determined to be on the red-giant branch, 2077 are red-clump and 439 are secondary-clump stars. We do not specifically identify the low-metallicity, horizontal-branch stars. The difference between red-clump and secondary-clump stars is dependent on the manner in which Helium burning is first initiated. We discuss that the way the boundary between these classifications is set may lead to mis-categorization in a small number of stars. The remaining 522 stars were not classified either because they lacked sufficient power in the dipole modes (so-called depressed dipole modes) or because of conflicting values in the parameters.
- ID:
- ivo://CDS.VizieR/J/ApJ/888/34
- Title:
- Robo-AO Kepler asteroseismic survey. II.
- Short Name:
- J/ApJ/888/34
- Date:
- 25 Oct 2021 10:08:41
- Publisher:
- CDS
- Description:
- The Kepler Space Telescope observed over 15000 stars for asteroseismic studies. Of these, 75% of dwarfs (and 8% of giants) were found to show anomalous behavior, such as suppressed oscillations (low amplitude) or no oscillations at all. The lack of solar-like oscillations may be a consequence of multiplicity, due to physical interactions with spectroscopic companions or due to the dilution of oscillation amplitudes from "wide" (AO detected; visual) or spectroscopic companions introducing contaminating flux. We present a search for stellar companions to 327 of the Kepler asteroseismic sample, which were expected to display solar-like oscillations. We used direct imaging with Robo-AO, which can resolve secondary sources at ~0.15", and followed up detected companions with Keck AO. Directly imaged companion systems with both separations of <=0.5" and amplitude dilutions >10% all have anomalous primaries, suggesting these oscillation signals are diluted by a sufficient amount of excess flux. We also used the high-resolution spectrometer ESPaDOnS at the Canada-France-Hawai'i Telescope to search for spectroscopic binaries. We find tentative evidence for a higher fraction of spectroscopic binaries with high radial velocity scatter in anomalous systems, which would be consistent with previous results suggesting that oscillations are suppressed by tidal interactions in close eclipsing binaries.
- « Previous
- Next »
- 1
- 2
- 3
- 4
