- ID:
- ivo://CDS.VizieR/J/ApJ/791/58
- Title:
- C and O abundances across the Hertzsprung gap
- Short Name:
- J/ApJ/791/58
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We derived atmospheric parameters and spectroscopic abundances for C and O for a large sample of stars located in the Hertzsprung gap in the Hertzsprung-Russell diagram in order to detect chemical peculiarities and get a comprehensive overview of the population of stars in this evolutionary state. We have observed and analyzed high-resolution spectra (R = 60,000) of 188 stars in the mass range 2-5 M_{sun}_ with the 2.7 m Harlan J. Smith Telescope at the McDonald Observatory including 28 stars previously identified as Am/Ap stars. We find that the C and O abundances of the majority of stars in the Hertzsprung gap are in accordance with abundances derived for local lower-mass dwarfs but detect expected peculiarities for the Am/Ap stars. The C and O abundances of stars with T_eff_< 6500 K are slightly lower than for the hotter objects but the C/O ratio is constant in the analyzed temperature domain. No indication of an alteration of the C and O abundances of the stars by mixing during the evolution across the Hertzsprung gap could be found before the homogenization of their atmospheres by the first dredge-up.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/628/A102
- Title:
- Carbon-rich (DQ) white dwarfs in SDSS
- Short Name:
- J/A+A/628/A102
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Among the spectroscopically identified white dwarfs, a fraction smaller than 2% have spectra dominated by carbon lines, mainly molecular C_2_, but also in a smaller group by CI and CII lines. These are together called DQ white dwarfs. We derive atmospheric parameters Teff, logg, and carbon abundances for a large sample of these stars and discuss implications for their spectral evolution. Sloan Digital Sky Survey spectra and ugriz photometry were used, together with Gaia Data Release 2 parallaxes and G band photometry. These were fitted to synthetic spectra and theoretical photometry derived from model atmospheres. We found that the DQs hotter than Teff ~10000K have masses ~0.4M_{sun}_ larger than the classical DQ, which have masses typical for the majority of white dwarfs (~0.6M_{sun}_). We found some evidence that the peculiar DQ below 10000K also have significantly larger masses and may thus be the descendants of the hot and warm DQs above 10000K. A significant fraction of the hotter objects with Teff>14500K have atmospheres dominated by carbon.
- ID:
- ivo://CDS.VizieR/J/A+A/390/967
- Title:
- Carbon-rich giants in the HR diagram
- Short Name:
- J/A+A/390/967
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- There are 513 entries corresponding to 513 SEDs of 410 carbon stars and related objects, and 70 Ba II stars. Absolute magnitude bolometric (Col. 7) are given for 348 348 (C & rel.) + 65 (Ba II) entries. Together with the effective temperatures previously obtained (Col. 5), they were used to draw the local HR diagram and the luminosity function for galactic carbon giants and related objects in the Sun vicinity. Also given in column 6, the apparent bolometric magnitudes, and in column 8 as ``remarks'', the variation phase information whenever available, the detection of circumstellar extinction and/or emission, the presence of Tc; the J-type, CH stars, carbon-Cepheids etc., are also shown. Our photometric solutions (photometric type in Col. 3 and interstellar extinction at J in Col. 4: to be multiplied by 1.145 to obtain E(B-V)).
- ID:
- ivo://CDS.VizieR/J/A+A/627/A161
- Title:
- CARMENES stars multi wavelength measurements
- Short Name:
- J/A+A/627/A161
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present precise photospheric parameters of 282 M dwarfs determined from fitting the most recent version of PHOENIX models to high-resolution CARMENES spectra in the visible (0.52-0.96um) and near-infrared wavelength range (0.96-1.71um). With its aim to search for habitable planets around M dwarfs, several planets of different masses have been detected. The characterization of the target sample is important for the ability to derive and constrain the physical properties of any planetary systems that are detected. As a continuation of previous work in this context, we derived the fundamental stellar parameters effective temperature, surface gravity, and metallicity of the CARMENES M-dwarf targets from PHOENIX model fits using a {chi}^2^ method. We calculated updated PHOENIX stellar atmosphere models that include a new equation of state to especially account for spectral features of low-temperature stellar atmospheres as well as new atomic and molecular line lists. We show the importance of selecting magnetically insensitive lines for fitting to avoid effects of stellar activity in the line profiles. For the first time, we directly compare stellar parameters derived from multi wavelength range spectra, simultaneously observed for the same star. In comparison with literature values we show that fundamental parameters derived from visible spectra and visible and near-infrared spectra combined are in better agreement than those derived from the same spectra in the near-infrared alone.
- ID:
- ivo://CDS.VizieR/J/A+A/656/A162
- Title:
- CARMENES stellar atmospheric parameters
- Short Name:
- J/A+A/656/A162
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- We determine effective temperatures, surface gravities, and metallicities for a sample of 343 M dwarfs observed with CARMENES, the double-channel, high-resolution spectrograph installed at the 3.5m telescope at Calar Alto Observatory. We employed SteParSyn, a Bayesian spectral synthesis implementation, along with a grid of synthetic spectra based on BT-Settl model atmospheres and the radiative transfer code turbospectrum. The synthetic grid was computed around 75 magnetically insensitive TiI and FeI along with the TiO gamma- and epsilon-bands. To avoid degeneracies in the parameter space, we imposed Bayesian priors based on multi-band photometric data available for the sample.
- ID:
- ivo://CDS.VizieR/J/A+A/657/A87
- Title:
- CASCADES I. Sample definition and first results
- Short Name:
- J/A+A/657/A87
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Following the first discovery of a planet orbiting a giant star in 2002, we started the CORALIE radial-velocity search for companions around evolved stars (CASCADES). We present the observations of three stars conducted at the 1.2m Leonard Euler Swiss telescope at La Silla Observatory, Chile, using the CORALIE spectrograph. We aim to detect planetary companions to intermediate-mass G- and K- type evolved stars and perform a statistical analysis of this population. We searched for new planetary systems around the stars HD22532 (TIC200851704), HD64121 (TIC264770836), and HD69123 (TIC146264536). We have followed a volume-limited sample of 641 red giants since 2006 to obtain high-precision radial-velocity measurements. We used the Data & Analysis Center for Exoplanets (DACE) platform to perform a radial-velocity analysis to search for periodic signals in the line profile and activity indices, to distinguish between planetary-induced radial-velocity variations and stellar photospheric jitter, and to search for significant signals in the radial-velocity time series to fit a corresponding Keplerian model. In this paper, we present the survey in detail, and we report on the discovery of the first three planets of the sample around the giant stars HD22532, HD64121, and HD69123.
- ID:
- ivo://CDS.VizieR/J/AJ/151/59
- Title:
- Catalog of Earth-Like Exoplanet Survey Targets
- Short Name:
- J/AJ/151/59
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Locating planets in circumstellar habitable zones (HZs) is a priority for many exoplanet surveys. Space-based and ground-based surveys alike require robust toolsets to aid in target selection and mission planning. We present the Catalog of Earth-Like Exoplanet Survey Targets (CELESTA), a database of HZs around 37000 nearby stars. We calculated stellar parameters, including effective temperatures, masses, and radii, and we quantified the orbital distances and periods corresponding to the circumstellar HZs. We gauged the accuracy of our predictions by contrasting CELESTA's computed parameters to observational data. We ascertain a potential return on investment by computing the number of HZs probed for a given survey duration. A versatile framework for extending the functionality of CELESTA into the future enables ongoing comparisons to new observations, and recalculations when updates to HZ models, stellar temperatures, or parallax data become available. We expect to upgrade and expand CELESTA using data from the Gaia mission as the data become available.
- ID:
- ivo://CDS.VizieR/J/AJ/161/189
- Title:
- Catalog of gyro-kinematic ages for ~30000 Kepler stars
- Short Name:
- J/AJ/161/189
- Date:
- 09 Mar 2022 22:00:00
- Publisher:
- CDS
- Description:
- Estimating stellar ages is important for advancing our understanding of stellar and exoplanet evolution and investigating the history of the Milky Way. However, ages for low-mass stars are hard to infer as they evolve slowly on the main sequence. In addition, empirical dating methods are difficult to calibrate for low-mass stars as they are faint. In this work, we calculate ages for Kepler F, G, and crucially K and M-dwarfs, using their rotation and kinematic properties. We apply the simple assumption that the velocity dispersion of stars increases over time and adopt an age-velocity-dispersion relation (AVR) to estimate average stellar ages for groupings of coeval stars. We calculate the vertical velocity dispersion of stars in bins of absolute magnitude, temperature, rotation period, and Rossby number and then convert velocity dispersion to kinematic age via an AVR. Using this method, we estimate gyro-kinematic ages for 29949 Kepler stars with measured rotation periods. We are able to estimate ages for clusters and asteroseismic stars with an rms of 1.22Gyr and 0.26Gyr respectively. With our Astraea machine-learning algorithm, which predicts rotation periods, we suggest a new selection criterion (a weight of 0.15) to increase the size of the McQuillan et al. catalog of Kepler rotation periods by up to 25%. Using predicted rotation periods, we estimated gyro-kinematic ages for stars without measured rotation periods and found promising results by comparing 12 detailed age-element abundance trends with literature values.
- ID:
- ivo://CDS.VizieR/J/A+A/600/A50
- Title:
- Catalog of hot subdwarf stars
- Short Name:
- J/A+A/600/A50
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In preparation for the upcoming all-sky data releases of the Gaia mission we compiled a catalog of known hot subdwarf stars and candidates drawn from the literature and yet unpublished databases. By matching this catalog with astrometric and photometric data from the Gaia mission, we will develop selection criteria to construct a homogeneous, magnitude-limited all-sky catalog of hot subdwarf stars based on Gaia data.
- ID:
- ivo://CDS.VizieR/J/ApJS/232/26
- Title:
- Catalog of Kepler flare stars
- Short Name:
- J/ApJS/232/26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We aim to perform a statistical study of stellar flares observed by Kepler. We want to study the flare amplitude, duration, energy, and occurrence rates, and how they are related to the spectral type and rotation period. To that end, we have developed an automated flare detection and characterization algorithm. We have harvested the stellar parameters from the Kepler input catalog and the rotation periods from McQuillan et al. (2014, Cat. J/ApJS/211/24). We find several new candidate A stars showing flaring activity. Moreover, we find 653 giants with flares. From the statistical distribution of flare properties, we find that the flare amplitude distribution has a similar behavior between F+G types and K+M types. The flare duration and flare energy seem to be grouped between G+K+M types versus F types and giants. We also detect a tail of stars with high flare occurrence rates across all spectral types (but most prominent in the late spectral types), and this is compatible with the existence of "flare stars." Finally, we have found a strong correlation of the flare occurrence rate and the flare amplitude with the stellar rotation period: a quickly rotating star is more likely to flare often and has a higher chance of generating large flares.