- ID:
- ivo://CDS.VizieR/J/AJ/154/259
- Title:
- Fundamental parameters of Tycho-2 & TGAS stars
- Short Name:
- J/AJ/154/259
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present bolometric fluxes and angular diameters for over 1.6 million stars in the Tycho-2 catalog (I/259), determined using previously determined empirical color-temperature and color-flux relations. We vet these relations via full fits to the full broadband spectral energy distributions for a subset of benchmark stars and perform quality checks against the large set of stars for which spectroscopically determined parameters are available from LAMOST, RAVE, and/or APOGEE. We then estimate radii for the 355502 Tycho-2 stars in our sample whose Gaia DR1 (I/337) parallaxes are precise to ~<10%. For these stars, we achieve effective temperature, bolometric flux, and angular diameter uncertainties of the order of 1%-2% and radius uncertainties of order 8%, and we explore the effect that imposing spectroscopic effective temperature priors has on these uncertainties. These stellar parameters are shown to be reliable for stars with T_eff_~<7000 K. The over half a million bolometric fluxes and angular diameters presented here will serve as an immediate trove of empirical stellar radii with the Gaia second data release, at which point effective temperature uncertainties will dominate the radius uncertainties. Already, dwarf, subgiant, and giant populations are readily identifiable in our purely empirical luminosity-effective temperature (theoretical) Hertzsprung-Russell diagrams.
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- ID:
- ivo://CDS.VizieR/J/A+A/573/A67
- Title:
- Fundamental stellar parameters from PolarBase
- Short Name:
- J/A+A/573/A67
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The general context of this study is the inversion of stellar fundamental parameters from high-resolution Echelle spectra. We aim at developing a fast and reliable tool for the post-processing of spectra produced by ESPaDOnS and Narval spectropolarimeters. Our inversion tool relies on principal component analysis. It allows reducing dimensionality and defining a specific metric for the search of nearest neighbours between an observed spectrum and a set of observed spectra taken from the Elodie stellar library. Effective temperature, surface gravity, total metallicity, and projected rotational velocity are derived. Various tests presented in this study that were based solely on information coming from a spectral band centred on the Mgi b-triplet and had spectra from FGK stars are very promising.
- ID:
- ivo://CDS.VizieR/J/AJ/162/126
- Title:
- FUV and optical absorption in 47 Tucanae
- Short Name:
- J/AJ/162/126
- Date:
- 14 Mar 2022 08:43:21
- Publisher:
- CDS
- Description:
- The Bright Star in the globular cluster 47Tucanae (NGC104) is a post-asymptotic giant branch (post-AGB) star of spectral type B8III. The ultraviolet spectra of late-B stars exhibit myriad absorption features, many due to species unobservable from the ground. The Bright Star thus represents a unique window into the chemistry of 47Tuc. We have analyzed observations obtained with the Far Ultraviolet Spectroscopic Explorer, the Cosmic Origins Spectrograph aboard the Hubble Space Telescope, and the Magellan Inamori Kyocera Echelle Spectrograph on the Magellan Telescope. By fitting these data with synthetic spectra, we determine various stellar parameters (Teff=10850{+/-}250K, logg=2.20{+/-}0.13) and the photospheric abundances of 26 elements, including Ne, P, Cl, Ga, Pd, In, Sn, Hg, and Pb, which have not previously been published for this cluster. Abundances of intermediate-mass elements (Mg through Ga) generally scale with Fe, while the heaviest elements (Pd through Pb) have roughly solar abundances. Its low C/O ratio indicates that the star did not undergo third dredge-up and suggests that its heavy elements were made by a previous generation of stars. If so, this pattern should be present throughout the cluster, not just in this star. Stellar-evolution models suggest that the Bright Star is powered by a He-burning shell, having left the AGB during or immediately after a thermal pulse. Its mass (0.54{+/-}0.16M{sun}) implies that single stars in 47Tuc lose 0.1-0.2M{sun} on the AGB, only slightly less than they lose on the red giant branch.
- ID:
- ivo://CDS.VizieR/J/ApJS/236/36
- Title:
- Ga, Ge, As, Kr, Cd, Sn and Pb column densities
- Short Name:
- J/ApJS/236/36
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an extensive analysis of the gas-phase abundances and depletion behaviors of neutron-capture elements in the interstellar medium (ISM). Column densities (or upper limits to the column densities) of Ga II, Ge II, As II, Kr I, Cd II, Sn II, and Pb II are determined for a sample of 69 sight lines with high- and/or medium-resolution archival spectra obtained with the Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope. An additional 59 sight lines with column density measurements reported in the literature are included in our analysis. Parameters that characterize the depletion trends of the elements are derived according to the methodology developed by Jenkins (2009, J/ApJ/700/1299). The depletion patterns exhibited by Ga and Ge comport with expectations based on the depletion results obtained for many other elements. Arsenic exhibits much less depletion than expected, and its abundance in low-depletion sight lines may even be supersolar. We confirm a previous finding by Jenkins that the depletion of Kr increases as the overall depletion level increases from one sight line to another. Cadmium shows no such evidence of increasing depletion. We find a significant amount of scatter in the gas-phase abundances of Sn and Pb. For Sn, at least, the scatter may be evidence of real intrinsic abundance variations due to s-process enrichment combined with inefficient mixing in the ISM.
- ID:
- ivo://CDS.VizieR/J/ApJ/874/138
- Title:
- Gaia and LAMOST DR4 M giant members of Sgr stream
- Short Name:
- J/ApJ/874/138
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use LAMOST DR4 M giants combined with Gaia DR2 proper motions and ALLWISE photometry to obtain an extremely pure sample of Sagittarius (Sgr) stream stars. Using TiO5 and CaH spectral indices as indicators, we selected a large sample of M-giant stars from M-dwarf stars in LAMOST DR4 spectra. Considering the position, distance, proper motion, and angular momentum distribution, we obtained 164 pure Sgr stream stars. We find that the trailing arm has higher energy than the leading arm in the same angular momentum. The trailing arm we detected extends to a heliocentric distance of ~130kpc at {Lambda}_{sun}_~170{deg}, which is consistent with the feature found in RR Lyrae in Sesar+ (2017, J/ApJ/844/L4). Both of these detections of Sgr, in M-giants and in RR Lyrae, imply that the Sgr stream may contain multiple stellar populations with a broad metallicity range.
- ID:
- ivo://CDS.VizieR/J/A+A/598/A5
- Title:
- Gaia-ESO Survey iDR4 calibrators
- Short Name:
- J/A+A/598/A5
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Gaia-ESO survey (GES) is now in its fifth and last year of observations and has produced tens of thousands of high-quality spectra of stars in all Milky Way components. This paper presents the strategy behind the selection of astrophysical calibration targets, ensuring that all GES results on radial velocities, atmospheric parameters, and chemical abundance ratios will be both internally consistent and easily comparable with other literature results, especially from other large spectroscopic surveys and from Gaia. The calibration of GES is particularly delicate because of (i) the large space of parameters covered by its targets, ranging from dwarfs to giants, from O to M stars; these targets have a large wide of metallicities and also include fast rotators, emission line objects, and stars affected by veiling; (ii) the variety of observing setups, with different wavelength ranges and resolution; and (iii) the choice of analyzing the data with many different state-of-the-art methods, each stronger in a different region of the parameter space, which ensures a better understanding of systematic uncertainties. An overview of the GES calibration and homogenization strategy is also given, along with some examples of the usage and results of calibrators in GES iDR4, which is the fourth internal GES data release and will form the basis of the next GES public data release. The agreement between GES iDR4 recommended values and reference values for the calibrating objects are very satisfactory. The average offsets and spreads are generally compatible with the GES measurement errors, which in iDR4 data already meet the requirements set by the main GES scientific goals.
- ID:
- ivo://CDS.VizieR/J/A+A/612/A99
- Title:
- Gaia-ESO Survey in 7 open star cluster fields
- Short Name:
- J/A+A/612/A99
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Determination and calibration of the ages of stars, which heavily rely on stellar evolutionary models, are very challenging, while representing a crucial aspect in many astrophysical areas. We describe the methodologies that, taking advantage of Gaia-DR1 and the Gaia-ESO Survey data, enable the comparison of observed open star cluster sequences with stellar evolutionary models. The final, long-term goal is the exploitation of open clusters as age calibrators. We perform a homogeneous analysis of eight open clusters using the Gaia-DR1 TGAS catalogue for bright members and information from the Gaia-ESO Survey for fainter stars. Cluster membership probabilities for the Gaia-ESO Survey targets are derived based on several spectroscopic tracers. The Gaia-ESO Survey also provides the cluster chemical composition. We obtain cluster parallaxes using two methods. The first one relies on the astrometric selection of a sample of bona fide members, while the other one fits the parallax distribution of a larger sample of TGAS sources. Ages and reddening values are recovered through a Bayesian analysis using the 2MASS magnitudes and three sets of standard models. Lithium depletion boundary (LDB) ages are also determined using literature observations and the same models employed for the Bayesian analysis. For all but one cluster, parallaxes derived by us agree with those presented in Gaia Collaboration (2017A&A...601A..19G, Cat. J/A+A/601/A19), while a discrepancy is found for NGC 2516; we provide evidence supporting our own determination. Inferred cluster ages are robust against models and are generally consistent with literature values. The systematic parallax errors inherent in the Gaia DR1 data presently limit the precision of our results. Nevertheless, we have been able to place these eight clusters onto the same age scale for the first time, with good agreement between isochronal and LDB ages where there is overlap. Our approach appears promising and demonstrates the potential of combining Gaia and ground-based spectroscopic datasets.
- ID:
- ivo://CDS.VizieR/J/A+A/591/A37
- Title:
- Gaia-ESO Survey. Parameters for cluster members
- Short Name:
- J/A+A/591/A37
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The nature of the metallicity gradient inside the solar circle (R_GC_<8kpc) is poorly understood, but studies of Cepheids and a small sample of open clusters suggest that it steepens in the inner disk. We investigate the metallicity gradient of the inner disk using a sample of inner disk open clusters that is three times larger than has previously been studied in the literature to better characterize the gradient in this part of the disk. We used the Gaia-ESO Survey (GES) [Fe/H] values and stellar parameters for stars in 12 open clusters in the inner disk from GES-UVES data. Cluster mean [Fe/H] values were determined based on a membership analysis for each cluster. Where necessary, distances and ages to clusters were determined via comparison to theoretical isochrones. The GES open clusters exhibit a radial metallicity gradient of -0.10+/-0.02dex/kpc, consistent with the gradient measured by other literature studies of field red giant stars and open clusters in the range R_GC_~6-12kpc. We also measure a trend of increasing [Fe/H] with increasing cluster age, as has also been found in the literature. We find no evidence for a steepening of the inner disk metallicity gradient inside the solar circle as earlier studies indicated. The age-metallicity relation shown by the clusters is consistent with that predicted by chemical evolution models that include the effects of radial migration, but a more detailed comparison between cluster observations and models would be premature.
- ID:
- ivo://CDS.VizieR/J/A+A/598/A68
- Title:
- Gaia-ESO Survey. Trumpler 23
- Short Name:
- J/A+A/598/A68
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Trumpler 23 is a moderately populated, intermediate-age open cluster within the solar circle at a R_GC_~6kpc. It is in a crowded field very close to the Galactic plane and the color-magnitude diagram shows significant field contamination and possible differential reddening; it is a relatively understudied cluster for these reasons, but its location makes it a key object for determining Galactic abundance distributions. New data from the Gaia-ESO Survey enable the first ever radial velocity and spectroscopic metallicity measurements for this cluster. We aim to use velocities to isolate cluster members, providing more leverage for determining cluster parameters. Gaia-ESO Survey data for 167 potential members have yielded radial velocity measurements, which were used to determine the systemic velocity of the cluster and membership of individual stars. Atmospheric parameters were also used as a check on membership when available. Literature photometry was used to re-determine cluster parameters based on radial velocity member stars only; theoretical isochrones are fit in the V, V-I diagram. Cluster abundance measurements of ten radial-velocity member stars with high-resolution spectroscopy are presented for 24 elements. These abundances have been compared to local disk stars, and where possible placed within the context of literature gradient studies. We find Trumpler 23 to have an age of 0.80+/-0.10Gyr, significant differential reddening with an estimated mean cluster E(V-I) of 1.02^+0.14^_-0.09_, and an apparent distance modulus of 14.15+/-0.20. We find an average cluster metallicity of [Fe/H]=0.14+/-0.03dex, a solar [{alpha}/Fe] abundance, and notably subsolar [s-process/Fe] abundances.
- ID:
- ivo://CDS.VizieR/J/A+A/582/A81
- Title:
- Gaia FGK benchmark stars: abundances
- Short Name:
- J/A+A/582/A81
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In the current era of large spectroscopic surveys of the Milky Way, reference stars for calibrating astrophysical parameters and chemical abundances are of paramount importance. We determine elemental abundances of Mg, Si, Ca, Sc, Ti, V, Cr, Mn, Co, and Ni for our predefined set of Gaia FGK benchmark stars. By analysing high-resolution spectra with a high signal-to-noise ratio taken from several archive datasets, we combined results of eight different methods to determine abundances on a line-by-line basis. We performed a detailed homogeneous analysis of the systematic uncertainties, such as differential versus absolute abundance analysis. We also assessed errors that are due to non-local thermal equilibrium and the stellar parameters in our final abundances.