- ID:
- ivo://CDS.VizieR/J/ApJ/869/157
- Title:
- ASTRAL: reference spectra for evolved M stars
- Short Name:
- J/ApJ/869/157
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Hubble Space Telescope (HST) Treasury Program Advanced Spectral Library Project: Cool Stars was designed to collect representative, high-quality UV spectra of eight evolved F-M type cool stars. The Space Telescope Imaging Spectrograph (STIS) echelle spectra of these objects enable investigations of a broad range of topics, including stellar and interstellar astrophysics. This paper provides a guide to the spectra of the two evolved M stars, the M2 Iab supergiant {alpha}Ori and the M3.4 giant {gamma}Cru, with comparisons to the prototypical K1.5 giant {alpha}Boo. It includes identifications of the significant atomic and molecular emission and absorption features and discusses the character of the photospheric and chromospheric continua and line spectra. The fluorescent processes responsible for a large portion of the emission-line spectrum, the characteristics of the stellar winds, and the available diagnostics for hot and cool plasmas are also summarized. This analysis will facilitate the future study of the spectra, outer atmospheres, and winds, not only of these objects but of numerous other cool, low-gravity stars, for years to come.
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- ID:
- ivo://CDS.VizieR/J/AJ/140/1911
- Title:
- Astrometric Grid Giant Star Survey. III.
- Short Name:
- J/AJ/140/1911
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results of high-resolution (~55000) spectral observations of 830 photometrically pre-selected candidate red giants in the magnitude range of V=9-12. We develop a pipeline for automated determination of the stellar atmospheric parameters from these spectra and estimate Teff, logg, [Fe/H], microturbulence velocity, and projected rotational velocities, vsin i, for the stars. The analysis confirms that the candidate selection procedure yielded red giants with very high success rate. We show that most of these stars are G and K giants with slightly subsolar metallicity ([Fe/H]~-0.3dex). An analysis of Mg abundances in the sample results in consistency of the [Mg/Fe] vs [Fe/H] trend with published results.
- ID:
- ivo://CDS.VizieR/J/ApJS/231/15
- Title:
- Astrometric monitoring of ultracool dwarf binaries
- Short Name:
- J/ApJS/231/15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the full results of our decade-long astrometric monitoring programs targeting 31 ultracool binaries with component spectral types M7-T5. Joint analysis of resolved imaging from Keck Observatory and Hubble Space Telescope and unresolved astrometry from CFHT/WIRCam yields parallactic distances for all systems, robust orbit determinations for 23 systems, and photocenter orbits for 19 systems. As a result, we measure 38 precise individual masses spanning 30-115M_Jup_. We determine a model-independent substellar boundary that is ~70M_Jup_ in mass (~L4 in spectral type), and we validate Baraffe et al. evolutionary model predictions for the lithium-depletion boundary (60M_Jup_ at field ages). Assuming each binary is coeval, we test models of the substellar mass-luminosity relation and find that in the L/T transition, only the Saumon & Marley (2008ApJ...689.1327S) "hybrid" models accounting for cloud clearing match our data. We derive a precise, mass-calibrated spectral type-effective temperature relation covering 1100-2800K. Our masses enable a novel direct determination of the age distribution of field brown dwarfs spanning L4-T5 and 30-70M_Jup_. We determine a median age of 1.3Gyr, and our population synthesis modeling indicates our sample is consistent with a constant star formation history modulated by dynamical heating in the Galactic disk. We discover two triple-brown-dwarf systems, the first with directly measured masses and eccentricities. We examine the eccentricity distribution, carefully considering biases and completeness, and find that low-eccentricity orbits are significantly more common among ultracool binaries than solar-type binaries, possibly indicating the early influence of long-lived dissipative gas disks. Overall, this work represents a major advance in the empirical view of very low-mass stars and brown dwarfs.
- ID:
- ivo://CDS.VizieR/J/AJ/154/147
- Title:
- Astrometry&photometry for late-type dwarfs&subdwarfs
- Short Name:
- J/AJ/154/147
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New, updated, and/or revised CCD parallaxes determined with the Strand Astrometric Reflector at the Naval Observatory Flagstaff Station are presented. Included are results for 309 late-type dwarf and subdwarf stars observed over the 30+ years that the program operated. For 124 of the stars, parallax determinations from other investigators have already appeared in the literature and we compare the different results. Also included here are new or updated VI photometry on the Johnson-Kron-Cousins system for all but a few of the faintest targets. Together with 2MASS JHK_s_ near-infrared photometry, a sample of absolute magnitude versus color and color versus color diagrams are constructed. Because large proper motion was a prime criterion for targeting the stars, the majority turn out to be either M-type subdwarfs or late M-type dwarfs. The sample also includes 50 dwarf or subdwarf L-type stars, and four T dwarfs. Possible halo subdwarfs are identified in the sample based on tangential velocity, subluminosity, and spectral type. Residuals from the solutions for parallax and proper motion for several stars show evidence of astrometric perturbations.
- ID:
- ivo://CDS.VizieR/J/A+AS/126/267
- Title:
- Atlas of Synthetic Spectra
- Short Name:
- J/A+AS/126/267
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A library of 711 cool star synthetic spectra in the wavelength range 485-540nm is presented. The coverage in the parameter space span in surface gravity from 1.0 to 5.0dex at a step of 0.5dex. The range in effective temperature covers from 4000 to 6000K at a step of 250K plus the spectra for 7000 and 8000K. The global chemical compositions are [M/H]=-1.0, -0.5, 0.0, +0.1, +0.2, +0.3 and +0.5. The adopted value of microturbulent velocity is 2km/s but for two sets of nine spectra each. All the spectra are computed at a resolving power =250,000. For each wavelength point the continuum and line blanketed absolute fluxes per unit frequency are given.
- ID:
- ivo://CDS.VizieR/J/A+A/616/A112
- Title:
- Atmospheric param. & abundances of red giants
- Short Name:
- J/A+A/616/A112
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent observational results have demonstrated an increase in the surface Na abundance that correlates with stellar mass for red giants between 2 and 3M_{sun}_. This trend supports evolutionary mixing processes as the explanation for Na overabundances seen in some red giants. In this same mass range, the surface Al abundance was shown to be constant. Our main aim was to extend the investigation of the Na and Al surface abundances to giants more massive than 3M_{sun}_. We sought to establish accurately whether the Na abundances keep increasing with stellar mass or a plateau is reached. In addition, we investigated whether mixing can affect the surface abundance of Al in giants more massive than 3M_{sun}_. We obtained new high-resolution spectra of 20 giants in the field of 10 open clusters; 17 of these stars were found to be members of 9 clusters. The giants have masses between 2.5M_{sun}_ and 5.6M_{sun}_. A model atmosphere analysis was performed and abundances of up to 22 elements were derived using equivalent widths. Additionally, abundances of C, N, and O were determined using spectrum synthesis. The abundances of Na and Al were corrected for non-local thermodynamic equilibrium (non-LTE) effects. Moreover, to extend the mass range of our sample, we collected from the literature high-quality C, N, O, and Na abundances of 32 Galactic Cepheids with accurate masses in the range between 3M_{sun}_ and 14M_{sun}_. The surface abundances of C, N, O, Na, and Al were compared to predictions of stellar evolution models with and without the inclusion of rotation-induced mixing. The surface abundances of most giants and Cepheids of the sample can be explained by models without rotation. For giants above ~2.5M_{sun}_, the Na abundances reach a plateau level of about [Na/Fe]~0.20-0.25dex (in non-LTE). This is true for both Cepheids and giants in open clusters. Regarding Al, the non-LTE [Al/Fe] ratios are mostly close to solar and suggest that Al is not affected by the first dredge-up up to ~5.0M_{sun}_. Our results support previous works that found models with rotation to overestimate the mixing effects in intermediate-mass stars.
- ID:
- ivo://CDS.VizieR/J/MNRAS/429/126
- Title:
- Atmospheric parameters from Fe lines
- Short Name:
- J/MNRAS/429/126
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a comprehensive analysis of different techniques available for the spectroscopic analysis of FGK stars and provide a recommended methodology which efficiently estimates accurate stellar atmospheric parameters for large samples of stars. Our analysis includes a simultaneous equivalent width analysis of FeI and FeII spectral lines, and for the first time, utilizes on-the-fly non-local thermodynamic equilibrium (NLTE) corrections of individual FeI lines. We further investigate several temperature scales, finding that estimates from Balmer line measurements provide the most accurate effective temperatures at all metallicities. We apply our analysis to a large sample of both dwarf and giant stars selected from the Radial Velocity Experiment (RAVE) survey. We then show that the difference between parameters determined by our method and that by the standard 1D LTE excitation-ionization balance of Fe reveals substantial systematic biases: up to 400K in effective temperature, 1.0dex in surface gravity and 0.4dex in metallicity for stars with [Fe/H]~-2.5. This has large implications for the study of the stellar populations in the Milky Way.
- ID:
- ivo://CDS.VizieR/J/ApJS/169/430
- Title:
- Atmospheric parameters of 1907 metal-rich stars
- Short Name:
- J/ApJS/169/430
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report high-precision atmospheric parameters for 1907 stars in the N2K low-resolution spectroscopic survey, designed to identify metal-rich FGK dwarfs likely to harbor detectable planets. Of these stars, 284 are in the ideal temperature range for planet searches, T_eff_<=6000K, and have a 10% or greater probability of hosting planets based on their metallicities. This catalog contains measurements of [Fe/H] (sigma_[Fe/H]_=0.07dex), T_eff_(sigma_Teff=82K), and logg (sigma_logg_=0.13dex). Atmospheric parameters are derived from Lick index measurements, as described in Robinson et al. (2006, Cat. <J/ApJ/637/1102>). Lick indices are measured from spectra obtained with the GCAM spectrograph on the 2.1m telescope at KPNO.
- ID:
- ivo://CDS.VizieR/J/PASJ/57/27
- Title:
- Atmospheric parameters of nearby F-K stars
- Short Name:
- J/PASJ/57/27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Based on a collection of high-dispersion spectra obtained at Okayama Astrophysical Observatory, the atmospheric parameters (Teff, logg, vt, and [Fe/H]) of 160 mid-F through early-K stars were extensively determined by the spectroscopic method using the equivalent widths of Fe I and Fe II lines along with the numerical technique of Takeda et al. (2002PASJ...54..451T). The results are comprehensively discussed and compared with the parameter values derived by different approaches (e.g., photometric colors, theoretical evolutionary tracks, Hipparcos parallaxes, etc.) as well as with the published values found in various literature. It has been confirmed that our purely spectroscopic approach yields fairly reliable and consistent results.
- ID:
- ivo://CDS.VizieR/J/A+A/645/A106
- Title:
- Atomic data for the Gaia-ESO Survey
- Short Name:
- J/A+A/645/A106
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We describe the atomic data that were used for the abundance analyses of FGK-type stars carried out within the Gaia-ESO Public Spectroscopic Survey in the years 2012 to 2019. The Gaia-ESO survey is one among several current and future stellar spectroscopic surveys producing abundances for Milky-Way stars on an industrial scale. We present an unprecedented effort to create a homogeneous common line list, which was used by several abundance analysis groups using different radiative transfer codes to calculate synthetic spectra and equivalent widths. The atomic data are accompanied by quality indicators and detailed references to the sources. An overview of molecular data is also given. Among a subset of over 1300 lines of 35 elements in the wavelength ranges from 475nm to 685nm and from 850nm to 895nm we identified about 200 lines of 24 species which have accurate gf-values and are free of blends in the spectra of the Sun and Arcturus.
