- ID:
- ivo://CDS.VizieR/J/A+A/517/A3
- Title:
- Stellar parameters of Kepler early-type targets
- Short Name:
- J/A+A/517/A3
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Stellar pulsation offers a unique opportunity to constrain the intrinsic parameters of stars and to unveil their inner structure. Kepler satellite is collecting a huge amount of data of unprecedent photometric precision, that will allow us to test theory and obtain a very precise tomography of stellar interiors. Aiming at providing the stars' fundamental parameters (Teff, logg, vsini, and luminosity) which are needed for computing asteroseismic models and interpreting Kepler data, we report spectroscopic observations of 23 early-type Kepler asteroseismic targets and 13 other stars in the Kepler field, but not selected to be observed. The cross-correlation with template spectra was used for measuring the radial velocity with the aim of identifying non-single stars. Spectral synthesis has been performed in order to derive the stellar parameters for our target stars. State-of-art LTE atmospheric models have been computed. For all the stars of our sample, we derive the radial velocity, Teff, logg, vsini, and luminosities. Further, for 12 stars, we perform a detailed abundance analysis of 20 species; for 16, we could derive only the [Fe/H] ratio. A spectral classification has been also performed for 17 stars in the sample. We found two double-lined spectroscopic binaries, HIP96299 and HIP98551, the former of which is an already known eclipsing binary, and two single-lined spectroscopic binaries, HIP97254 and HIP97724. We also report two suspected spectroscopic binaries, HIP92637 and HIP96762, and the detection of a possible variability of the radial velocity of HIP96277. Two of our program stars turn out to be chemically peculiar, namely HIP93941, which we classify as B2 He-weak, and HIP96210, which we classify as B6Mn. Finally, we find that HIP93522, HIP93941, HIP93943, HIP96210 and HIP96762, are very slow rotators (vsini<20km/s) which makes them very interesting and promising targets for an asteroseismic modeling.
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Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/159/193
- Title:
- Stellar parameters of ~30000 LAMOST DR1 M dwarfs
- Short Name:
- J/AJ/159/193
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- M-dwarfs are the most common type of star in the Galaxy, and because of their small size are favored targets for searches of Earth-sized transiting exoplanets. Current and upcoming all-sky spectroscopic surveys, such as the Large Sky Area Multi Fiber Spectroscopic Telescope (LAMOST), offer an opportunity to systematically determine physical properties of many more M dwarfs than has been previously possible. Here, we present new effective temperatures, radii, masses, and luminosities for 29678 M dwarfs with spectral types M0-M6 in the first data release (DR1) of LAMOST. We derived these parameters from the supervised machine-learning code, The Cannon, trained with 1388 M-dwarfs in the Transiting Exoplanet Survey Satellite Cool Dwarf Catalog that were also present in LAMOST with high signal-to-noise ratio (>250) spectra. Our validation tests show that the output parameter uncertainties are strongly correlated with the signal-to-noise of the LAMOST spectra, and we achieve typical uncertainties of 110K in T_eff_(~3%), 0.065R_{sun}_(~14%) in radius, 0.054M_{sun}_(~12%) in mass, and 0.012L_{sun}_(~20%) in luminosity. The model presented here can be rapidly applied to future LAMOST data releases, significantly extending the samples of well-characterized M dwarfs across the sky using new and exclusively data-based modeling methods.
- ID:
- ivo://CDS.VizieR/J/ApJ/750/L37
- Title:
- Stellar parameters of low-mass KOIs
- Short Name:
- J/ApJ/750/L37
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report stellar parameters for late-K and M-type planet-candidate host stars announced by the Kepler Mission. We obtained medium-resolution, K-band spectra of 84 cool (T_eff_<~4400K) Kepler Objects of Interest (KOIs) from Borucki et al (2011, Cat. J/ApJ/728/117). We identified one object as a giant (KOI 977); for the remaining dwarfs, we measured effective temperatures (T_eff_) and metallicities [M/H] using the K-band spectral indices of Rojas-Ayala et al (2012, Cat. J/ApJ/748/93). We determine the masses (M_*_) and radii (R_*_) of the cool KOIs by interpolation onto the Dartmouth evolutionary isochrones. The resultant stellar radii are significantly less than the values reported in the Kepler Input Catalog and, by construction, correlate better with T_eff_. Applying the published KOI transit parameters to our stellar radius measurements, we report new physical radii for the planet candidates. Recalculating the equilibrium temperatures of the planet-candidates assuming Earth's albedo and re-radiation fraction, we find that three of the planet-candidates are terrestrial sized with orbital semimajor axes that lie within the habitable zones of their host stars (KOI 463.01, KOI 812.03, and KOI 854.01).
- ID:
- ivo://CDS.VizieR/J/A+A/658/A194
- Title:
- Stellar parameters of 18 M dwarfs
- Short Name:
- J/A+A/658/A194
- Date:
- 24 Feb 2022 06:38:20
- Publisher:
- CDS
- Description:
- Deriving metallicities for solar-like stars follows well-established methods, but for cooler stars such as M dwarfs, the determination is much more complicated due to forests of molecular lines that are present. Several methods have been developed in recent years to determine accurate stellar parameters for these cool stars (Teff<4000K). However, significant differences can be found at times when comparing metallicities for the same star derived using different methods. In this work, we determine the effective temperatures, surface gravities, and metallicities of 18 well-studied M dwarfs observed with the CARMENES high-resolution spectrograph following different approaches, including synthetic spectral fitting, analysis of pseudo-equivalent widths, and machine learning. We analyzed the discrepancies in the derived stellar parameters, including metallicity, in several analysis runs. Our goal is to minimize these discrepancies and find stellar parameters that are more consistent with the literature values. We attempted to achieve this consistency by standardizing the most commonly used components, such as wavelength ranges, synthetic model spectra, continuum normalization methods, and stellar parameters. We conclude that although such modifications work quite well for hotter main-sequence stars, they do not improve the consistency in stellar parameters for M dwarfs, leading to mean deviations of around 50-200K in temperature and 0.1-0.3dex in metallicity. In particular, M dwarfs are much more complex and a standardization of the aforementioned components cannot be considered as a straightforward recipe for bringing consistency to the derived parameters. Further in-depth investigations of the employed methods would be necessary in order to identify and correct for the discrepancies that remain.
- ID:
- ivo://CDS.VizieR/J/A+A/614/A146
- Title:
- Stellar parameters of NGC3201 RGB stars
- Short Name:
- J/A+A/614/A146
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The origin of the globular cluster (GC) NGC3201 is under debate. Its retrograde orbit points to an extragalactic origin, but no further chemical evidence supports this idea. Light-element chemical abundances are useful to tag GCs and can be used to shed light in this discussion. Recently it was shown that the CN and CH indices are useful to identify anomalous GCs out of typical Milky Way GCs. A possible origin of anomalous clusters is the merger of two GCs and/or nucleus of a dwarf galaxy. We aim at deriving CN and CH band strengths for red giant stars in NGC3201 and compare with photometric indices and high-resolution spectroscopy and discuss in the context of GC chemical tagging. We measure molecular band indices of S(3839) and G4300 for CN and CH, respectively from low-resolution spectra of red giant stars. Gravity and temperature effects are removed. Photometric indices are used to indicate further chemical information on C+N+O or s-process element abundances, not derived from low-resolution spectra. We found three groups on the CN-CH distribution. A main sequence (S1), a secondary less-populated sequence (S2), and a group of peculiar (pec) CN-weak and CH-weak stars, one of which was previously known. The three groups seem to have different C+N+O and/or s-process element abundances, to be confirmed by high-resolution spectroscopy. These are typical characteristics of anomalous GCs. The CN distribution of NGC3201 is quadrimodal, which is more common in anomalous clusters. However, NGC3201 does not belong to the trend of anomalous GCs in the mass-size relation. NGC3201 shows signs that it can be chemically tagged as anomalous: unusual CN-CH relation, indications that pec-S1-S2 is an increasing sequence of C+N+O or s-process element abundances, and a multimodal CN distribution that seems to correlate with s-process element abundances. The differences are: it has a debatable Fe-spread and it does not follow the trend of mass-size of all anomalous clusters. Three scenarios are postulated here: (i) if the sequence pec-S1-S2 has increasing C+N+O and s-process element abundances, NGC3201 would be the first anomalous GC out of the mass-size relation; (ii) if the abundances are almost constant, NGC3201 would be the first non-anomalous GC with multiple CN-CH anti-correlation groups, or (iii) it would be the first anomalous GC without variations in C+N+O and s-process element abundances. In all cases, the definition of anomalous clusters and the scenario where they have an extragalactic origin must be revised.
- ID:
- ivo://CDS.VizieR/J/A+A/474/1081
- Title:
- Stellar population gradients in bulges. I
- Short Name:
- J/A+A/474/1081
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This is the first paper presenting our long-term project aimed at studying the nature of bulges through analyzing their stellar population gradients. We present deep spectroscopic observations along the minor axis and the data reduction for a sample of 32 bulges of edge-on spiral galaxies. We explain in detail our procedures for measuring their dynamical parameters (rotation curves and velocity dispersion profiles) and line-strength indices, including the conversion to the Lick/IDS system. Tables giving the values of the dynamical parameters and line-strength indices at each galactocentric radius are presented (in electronic form) for each galaxy of the sample. The derived line-strength gradients from this dataset will be analyzed in a forthcoming paper to set constraints on the different scenarios for the formation of the bulges.
- ID:
- ivo://CDS.VizieR/J/ApJ/764/154
- Title:
- Stellar populations in the central 0.5pc. I.
- Short Name:
- J/ApJ/764/154
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new high angular resolution near-infrared spectroscopic observations of the nuclear star cluster surrounding the Milky Way's central supermassive black hole. Using the integral-field spectrograph OSIRIS on Keck II behind the laser-guide-star adaptive optics system, this spectroscopic survey enables us to separate early-type (young, 4-6Myr) and late-type (old, >1Gyr) stars with a completeness of 50% down to K'=15.5mag, which corresponds to ~10M_{sun}_ for the early-type stars. This work increases the radial extent of reported OSIRIS/Keck measurements by more than a factor of three from 4" to 14" (0.16 to 0.56pc), along the projected disk of young stars. For our analysis, we implement a new method of completeness correction using a combination of star-planting simulations and Bayesian inference. We assign probabilities for the spectral type of every source detected in deep imaging down to K'=15.5mag using information from spectra, simulations, number counts, and the distribution of stars. The inferred radial surface-density profiles, {Sigma}(R){prop.to}R^-{Gamma}^, for the young stars and late-type giants are consistent with earlier results ({Gamma}_early_=0.93+/-0.09, {Gamma}_late_=0.16+/-0.07). The late-type surface-density profile is approximately flat out to the edge of the survey. While the late-type stellar luminosity function is consistent with the Galactic bulge, the completeness-corrected luminosity function of the early-type stars has significantly more young stars at faint magnitudes compared with previous surveys with similar depth. This luminosity function indicates that the corresponding mass function of the young stars is likely less top-heavy than that inferred from previous surveys.
- ID:
- ivo://CDS.VizieR/J/MNRAS/409/1455
- Title:
- Stellar populations of early-type galaxies
- Short Name:
- J/MNRAS/409/1455
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The influence of environment on the formation and evolution of early-type galaxies is, as yet, an unresolved issue. Constraints can be placed on models of early-type galaxy formation and evolution by examining their stellar populations as a function of environment. We present a catalogue of galaxies well suited to such an investigation. The magnitude-limited (b_J_<=19.45) sample was drawn from four clusters (Coma, A1139, A3558 and A930 at <z>=0.04) and their surrounds. The catalogue contains luminosities, redshifts, velocity dispersions and Lick line strengths for 416 galaxies, of which 245 are classified as early types. Luminosity-weighted ages, metallicities and {alpha}-element abundance ratios have been estimated for 219 of these early types. We also outline the steps necessary for measuring fully calibrated Lick indices and estimating the associated stellar population parameters using up-to-date methods and stellar population models. In a subsequent paper we perform a detailed study of the stellar populations of early-type galaxies in clusters and investigate the effects of environment.
- ID:
- ivo://CDS.VizieR/J/A+A/618/A156
- Title:
- Stellar populations of the central region of M31
- Short Name:
- J/A+A/618/A156
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We continue the analysis of the data set of our spectroscopic observation campaign of M31, whose ultimate goal is to provide an understanding of the three-dimensional structure of the bulge, its formation history, and composition in terms of a classical bulge, boxy-peanut bulge, and bar contributions. We derive simple stellar population (SSP) properties, such as age metallicity and alpha-element overabundance, from the measurement of Lick/IDS absorption line indices. We describe their two-dimensional maps taking into account the dust distribution in M31. We found 80% of the values of our age measurements are larger than 10Gyr. The central 100-arcsec of M31 are dominated by the stars of the classical bulge of M31. These stars are old (11-13Gyr), metal-rich (as high as [Z/H]~0.35dex) at the center with a negative gradient outward and enhanced in alpha-elements ([alpha/Fe]~0.28+/-0.01dex). The bar stands out in the metallicity map, where an almost solar value of [Z/H] (~0.02+/-0.01dex) with no gradient is observed along the bar position angle (55.7{deg}) out to 600 arcsec from the center. In contrast, no signature of the bar is seen in the age and [alpha/Fe] maps, which are approximately axisymmetric, delivering a mean age and overabundance for the bar and boxy-peanut bulge of 10-13Gyr and 0.25-0.27dex, respectively. The boxy-peanut bulge has almost solar metallicity (-0.04+/-0.01dex). The mass-to-light ratio of the three components is approximately constant at M/LV~4.4-4.7M_{sun}_/L_{sun}_. The disk component at larger distances is made of a mixture of stars, as young as 3-4Gyr, with solar metallicity and smaller M/LV (~3+/-0.1M_{sun}_/L_{sun}_). We propose a two-phase formation scenario for the inner region of M31, where most of the stars of the classical bulge come into place together with a proto-disk, where a bar develops and quickly transforms it into a boxy-peanut bulge. Star formation continues in the bulge region, producing stars younger than 10Gyr, in particular along the bar, thereby enhancing its metallicity. The disk component appears to build up on longer timescales.
- ID:
- ivo://CDS.VizieR/J/ApJ/648/591
- Title:
- Stellar rotation in young clusters. II.
- Short Name:
- J/ApJ/648/591
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We derive the effective temperatures and gravities of 461 OB stars in 19 young clusters by fitting the H{gamma} profile in their spectra. We use synthetic model profiles for rotating stars to develop a method to estimate the polar gravity for these stars, which we argue is a useful indicator of their evolutionary status. We combine these results with projected rotational velocity measurements obtained in a previous paper on these same open clusters.
