- ID:
- ivo://CDS.VizieR/J/A+A/589/A61
- Title:
- Stellar parameters and abundances for M30
- Short Name:
- J/A+A/589/A61
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The prediction of the PLANCK-constrained primordial lithium abundance in the Universe is in discordance with the observed Li abundances in warm Population II dwarf and subgiant stars. Among the physically best motivated ideas, it has been suggested that this discrepancy can be alleviated if the stars observed today had undergone photospheric depletion of lithium. The cause of this depletion is investigated by accurately tracing the behaviour of the lithium abundances as a function of effective temperature. Globular clusters are ideal laboratories for such an abundance analysis as the relative stellar parameters of their stars can be precisely determined. We performed a homogeneous chemical abundance analysis of 144 stars in the metal-poor globular cluster M30, ranging from the cluster turnoff point to the tip of the red giant branch. Non-local thermal equilibrium (NLTE) abundances for Li, Ca, and Fe were derived where possible by fitting spectra obtained with VLT/FLAMES-GIRAFFE using the quantitative-spectroscopy package SME. Stellar parameters were derived by matching isochrones to the observed V vs V-I colour-magnitude diagram. Independent effective temperatures were obtained from automated profile fitting of the Balmer lines and by applying colour-Teff calibrations to the broadband photometry.
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- ID:
- ivo://CDS.VizieR/J/A+A/567/A72
- Title:
- Stellar parameters and abundances in NGC 6752
- Short Name:
- J/A+A/567/A72
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Abundance trends in heavier elements with evolutionary phase have been shown to exist in the globular cluster NGC 6752. These trends are a result of atomic diffusion and additional (non-convective) mixing. Studying such trends can provide us with important constraints on the extent to which diffusion modifies the internal structure and surface abundances of solar-type, metal-poor stars. Taking advantage of a larger data sample, we investigate the reality and the size of these abundance trends and address questions and potential biases associated with the various stellar populations that make up NGC 6752. We perform an abundance analysis by combining photometric and spectroscopic data of 194 stars located between the turnoff point and the base of the red giant branch. Stellar parameters are derived from uvby Stromgren photometry. Using the quantitative-spectroscopy package SME, stellar surface abundances for light elements such as Li, Na, Mg, Al, and Si as well as heavier elements such as Ca, Ti, and Fe are derived in an automated way by fitting synthetic spectra to individual lines in the stellar spectra, obtained with the VLT/FLAMES-GIRAFFE spectrograph. Based on uvby Stromgren photometry, we are able to separate three stellar populations in NGC 6752 along the evolutionary sequence from the base of the red giant branch down to the turnoff point. We find weak systematic abundance trends with evolutionary phase for Ca, Ti, and Fe which are best explained by stellar-structure models including atomic diffusion with efficient additional mixing. We derive a new value for the initial lithium abundance of NGC 6752 after correcting for the effect of atomic diffusion and additional mixing which falls slightly below the predicted standard BBN value. We find three stellar populations by combining photometric and spectroscopic data of 194 stars in the globular cluster NGC 6752. Abundance trends for groups of elements, differently affected by atomic diffusion and additional mixing, are identified. Although the statistical significance of the individual trends is weak, they all support the notion that atomic diffusion is operational along the evolutionary sequence of NGC 6752.
- ID:
- ivo://CDS.VizieR/J/MNRAS/411/435
- Title:
- Stellar parameters and extinction
- Short Name:
- J/MNRAS/411/435
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Astrometric surveys provide the opportunity to measure the absolute magnitudes of large numbers of stars, but only if the individual line-of-sight extinctions are known. Unfortunately, extinction is highly degenerate with stellar effective temperature when estimated from broad band optical/infrared photometry. To address this problem, I introduce a Bayesian method for estimating the intrinsic parameters of a star and its line-of-sight extinction.
- ID:
- ivo://CDS.VizieR/J/MNRAS/427/1153
- Title:
- Stellar parameters of giants in {omega} Cen
- Short Name:
- J/MNRAS/427/1153
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have determined stellar parameters and abundances for 221 giant branch stars in the globular cluster omega Centauri. A combination of photometry and lower-resolution spectroscopy was used to determine temperature, gravity, metallicity, [C/Fe], [N/Fe] and [Ba/Fe]. These abundances agree well with those found by previous researchers and expand the analysed sample of the cluster. k-means clustering analysis was used to group the stars into four homogeneous groups based upon these abundances. These stars show the expected anticorrelation in [C/Fe] to [N/Fe]. We investigated the distribution of CN-weak/strong stars on the colour-magnitude diagram. Asymptotic giant branch stars, which were selected from their position on the colour-magnitude diagram, were almost all CN-weak. This is in contrast to the red giant branch where a large minority were CN-strong. The results were also compared with cluster formation and evolution models. Overall, this study shows that statistically significant elemental and evolutionary conclusions can be obtained from lower resolution spectroscopy.
- 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.
- ID:
- ivo://CDS.VizieR/J/ApJ/788/L9
- Title:
- Stellar parameters of KIC planet-host stars
- Short Name:
- J/ApJ/788/L9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Most extrasolar planets have been detected by their influence on their parent star, typically either gravitationally (the Doppler method) or by the small dip in brightness as the planet blocks a portion of the star (the transit method). Therefore, the accuracy with which we know the masses and radii of extrasolar planets depends directly on how well we know those of the stars, the latter usually determined from the measured stellar surface gravity, log g. Recent work has demonstrated that the short-timescale brightness variations ("flicker") of stars can be used to measure log g to a high accuracy of ~0.1-0.2 dex. Here, we use flicker measurements of 289 bright (Kepmag<13) candidate planet-hosting stars with T_eff_=4500-6650 K to re-assess the stellar parameters and determine the resulting impact on derived planet properties. This re-assessment reveals that for the brightest planet-host stars, Malmquist bias contaminates the stellar sample with evolved stars: nearly 50% of the bright planet-host stars are subgiants. As a result, the stellar radii, and hence the radii of the planets orbiting these stars, are on average 20%-30% larger than previous measurements had suggested.
- ID:
- ivo://CDS.VizieR/J/AJ/158/56
- Title:
- Stellar parameters of M and K dwarfs
- Short Name:
- J/AJ/158/56
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Empirical correlations between stellar parameters such as rotation or radius and magnetic activity diagnostics require estimates of the effective temperatures and the stellar radii. The aim of this study is to propose simple methods that can be applied to large samples of stars in order to derive estimates of the stellar parameters. Good empirical correlations between red/infrared colors (e.g., (R-I)_C_) and effective temperatures have been well established for a long time. The more recent (R-I)_C_ color-T_eff_ correlation using the data of Mann et al. (2015, J/ApJ/804/64, hereafter M15) and Boyajian et al. (2012, J/ApJ/757/112, hereafter B12) shows that this color can be applied as a temperature estimate for large samples of stars. We find that the mean scatter in T_eff_ relative to the (R-I)_C_-T_eff_ relationship of B12 and M15 data is only +/-3{sigma}=44.6 K for K dwarfs and +/-3{sigma}=39.4 K for M dwarfs. These figures are small and show that the (R-I)_C_ color can be used as a first-guess effective temperature estimator for K and M dwarfs. We derive effective temperatures for about 1910 K and M dwarfs using the calibration of (R-I)_C_ color-T_eff_ from B12 and M15 data. We also compiled T_eff_ and metallicity measurements available in the literature using the VizieR database. We determine T_eff_ for 441 stars with previously unknown effective temperatures. We also identified 21 new spectroscopic binaries and one triple system from our high-resolution spectra.
- ID:
- ivo://CDS.VizieR/II/237
- Title:
- Stellar Photometry in Johnson's 11-color system
- Short Name:
- II/237
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This catalogue gives photometric data in the UBVRIJHKLMN colors and some additional information. Data for the JHKLMN bands come from NASA Ref. Pub. 1294 (1993). More complete information is found in Wisconsin Astrophysics 504 (1993) The effective wavelength of the Johsnon filters are: U = 360 nm B = 450 nm V = 555 nm R = 670 nm I = 870 nm J = 1.2 um H = 1.62um K = 2.2 um L = 3.5 um M = 5.0 um N = 9.0 um
- ID:
- ivo://CDS.VizieR/J/A+A/568/A119
- Title:
- Stellar physical parameters for young stars
- Short Name:
- J/A+A/568/A119
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A uvbyH{beta} Stromgren photometric survey covering 16 square degrees in the anticenter direction was carried out using the Wide Field Camera at the Isaac Newton Telescope. Physical parameters like stellar distances and extinctions for the young stars of our survey are presented here. We developed a new method for deriving physical parameters from Stromgren photometry and also implemented and tested it. This is a model-based method that uses the most recent available stellar atmospheric models and evolutionary tracks to interpolate in a 3D grid of the unreddened indexes [m1], [c1] and H{beta}. Distances derived from both this method and the classical pre-Hipparcos calibrations were tested against Hipparcos parallaxes and found to be accurate. Furthermore, a shift in the atmospheric grids in the range Teff=[7000,9000]K was detected and a correction is proposed. The two methods were used to compute distances and reddening for around 12000 OBA-type stars in our Stromgren anticenter survey. Data from the IPHAS and 2MASS catalogs were used to complement the detection of emission line stars and to break the degeneracy between early and late photometric regions. We note that photometric distances can differ by more than 20%, those derived from the empirical calibrations being smaller than those derived with the new method, which agree better with the Hipparcos data.
- ID:
- ivo://CDS.VizieR/J/ApJS/173/104
- Title:
- Stellar population in Chamaeleon I
- Short Name:
- J/ApJS/173/104
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- I present a new census of the stellar population in the ChamaeleonI star-forming region. Using optical and near-IR photometry and follow-up spectroscopy, I have discovered 50 new members of ChamaeleonI, expanding the census of known members to 226 objects. Fourteen of these new members have spectral types later than M6, which doubles the number of known members that are likely to be substellar. I have estimated extinctions, luminosities, and effective temperatures for the known members, used these data to construct an H-R diagram for the cluster, and inferred individual masses and ages with the theoretical evolutionary models of Baraffe and Chabrier. The low-mass stars are more widely distributed than members at other masses in the northern subcluster, but this is not the case in the southern subcluster. Meanwhile, the brown dwarfs have the same spatial distribution as the stars out to a radius of 3{deg} (8.5pc) from the center of ChamaeleonI.
