- ID:
- ivo://CDS.VizieR/J/AJ/157/167
- Title:
- Equivalent widths for RSGs in the MW & LMC/SMC
- Short Name:
- J/AJ/157/167
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Red supergiants (RSGs) are evolved massive stars that represent extremes, in both their physical sizes and their cool temperatures, of the massive star population. The effective temperature (T_eff_) is the most critical physical property needed to place an RSG on the Hertzsprung-Russell Diagram, due to the stars' cool temperatures and resulting large bolometric corrections. Several recent papers have examined the potential utility of atomic line equivalent widths (EWs) in cool supergiant (CSG) spectra for determining T_eff_ and other physical properties and found strong correlations between Ti I and Fe I spectral features and T_eff_ in earlier-type CSGs (G and early K) but poor correlations in M-type stars, a spectral subtype that makes up a significant fraction of RSGs. We have extended this work by measuring the EWs of Ti, Fe, and Ca lines in late K- and M-type RSGs in the Milky Way, Large Magellanic Cloud, and Small Magellanic Cloud, and compared these results to the predictions of the theoretical stellar LTE atmosphere models (MARCS) stellar atmosphere models. Our analyses show a poor correlation between T_eff_ and the Fe I and Ti I lines in our observations (at odds with strong correlations predicted by stellar atmosphere models), but do find statistically significant correlations between T_eff_ and the Ca II triplet (CaT) features of Milky Way RSGs, suggesting that this could be a potential diagnostic tool for determining T_eff_ in M-type supergiants. We also examine correlations between these spectral features and other physical properties of RSGs (including metallicity, surface gravity, and bolometric magnitude), and consider the underlying physics driving the evolution of atomic line spectra in RSGs.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+AS/42/391
- Title:
- Equivalent Widths in Pollux
- Short Name:
- J/A+AS/42/391
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (no description available)
- ID:
- ivo://CDS.VizieR/J/A+A/549/A129
- Title:
- Equivalent widths of cool stars
- Short Name:
- J/A+A/549/A129
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The near-infrared (NIR) wavelength range offers some unique spectral features, and it is less prone to the extinction than the optical one. Recently, the first flux calibrated NIR library of cool stars from the NASA Infrared Telescope Facility (IRTF) have become available, and it has not been fully exploited yet. We want to develop spectroscopic diagnostics for stellar physical parameters based on features in the wavelength range 1-5um. In this work we test the technique in the I and K bands. The study of the Y, J, H, and L bands will be presented in the following paper. An objective method for semi-empirical definition of spectral features sensitive to various physical parameters is applied to the spectra. It is based on sensitivity map - i.e., derivative of the flux in the spectra with respect to the stellar parameters at a fixed wavelength. New optimized indices are defined and their equivalent widths (EWs) are measured.
- ID:
- ivo://CDS.VizieR/J/A+A/503/545
- Title:
- Equivalent widths of Li, Na, Fe, Ca in NGC 6397
- Short Name:
- J/A+A/503/545
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To alleviate the discrepancy between the prediction of the primordial lithium abundance in the universe and the abundances observed in Pop II dwarfs and subgiant stars, it has been suggested that the stars observable today have undergone photospheric depletion of lithium. To identify the cause of such depletion, it is important to accurately establish the behaviour of lithium abundance with effective temperature and evolutionary phase. Stars in globular clusters are ideal objects for such abundance analysis, as relative stellar parameters can be precisely determined. We conduct a homogeneous analysis of a very large sample of stars in the metal-poor globular cluster NGC 6397, covering well all evolutionary phases from below the main sequence turn-off to high up the red giant branch. Non-LTE Li abundances or abundance upper limits are obtained for all stars, and for a size-able sub-set of the targets also Na abundances are obtained. The sodium abundances are used to distinguish stars formed out of pristine material from stars formed out of material affected by pollution from a previous generation of more massive stars. The dwarfs, turn-off, and early subgiant stars in our sample form a thin abundance plateau, disrupted in the middle of the subgiant branch by the lithium dilution caused by the first dredge-up. A second steep abundance drop is seen at the luminosity of the red giant branch bump. The turn-off stars are more lithium-poor, by up to 0.1dex, than subgiants that have not yet undergone dredge-up. In addition, hotter dwarfs are slightly more lithium-poor than cooler dwarfs, which may be a signature of the so-called Li dip in the cluster, commonly seen among PopI stars. The feature is however weak. A considerably large spread in Na abundance confirms that NGC6397 has suffered from intra-cluster pollution in its infancy and a limited number of Na-enhanced and Li-deficient stars strongly contribute to form a significant anti-correlation between the abundances of Na and Li. It is nevertheless seen that lithium abundances are unaffected by relatively high degrees of pollution. Lithium abundance trends with effective temperature and stellar luminosity are compared to predictions from stellar structure models including atomic diffusion and ad-hoc turbulence below the convection zone. We confirm previous findings that some turbulence, with strict limits to its efficiency, is necessary to explain the observations.
- ID:
- ivo://CDS.VizieR/J/A+A/440/1153
- Title:
- Equivalent widths of 7 thin-disk stars
- Short Name:
- J/A+A/440/1153
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In Papers I (del Peloso et al. 2005, Cat. <J/A+A/434/275>) and II (2005A&A...434..301D) we performed the first determination of the age of the Galactic thin disk from Th/Eu nucleocosmochronology. The present work aimed at reducing the age uncertainty by expanding the stellar sample with the inclusion of seven new objects. The Th and Eu abundances used in the dating procedure were obtained through spectral synthesis, and to perform the synthesis it was necessary to know the atmospheric parameters and chemical abundances of contaminating elements.
- ID:
- ivo://CDS.VizieR/J/A+A/594/A106
- Title:
- eta Car velocity-resolved imaging
- Short Name:
- J/A+A/594/A106
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The mass loss from massive stars is not understood well. eta Carinae is a unique object for studying the massive stellar wind during the luminous blue variable phase. It is also an eccentric binary with a period of 5.54yr. The nature of both stars is uncertain, although we know from X-ray studies that there is a wind-wind collision whose properties change with orbital phase. We want to investigate the structure and kinematics of eta Car's primary star wind and wind-wind collision zone with a high spatial resolution of ~6mas (~14au) and high spectral resolution of R=12000. Observations of eta Car were carried out with the ESO Very Large Telescope Interferometer (VLTI) and the AMBER instrument between approximately five and seven months before the August 2014 periastron passage. Velocity-resolved aperture-synthesis images were reconstructed from the spectrally dispersed interferograms. Interferometric studies can provide information on the binary orbit, the primary wind, and the wind collision.
- ID:
- ivo://CDS.VizieR/J/A+A/644/A67
- Title:
- EUV estimates from CaII H&K activity
- Short Name:
- J/A+A/644/A67
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Atmospheric escape is an important factor shaping the exoplanet population and hence drives our understanding of planet formation. Atmospheric escape from giant planets is driven primarily by the stellar X-ray and extreme- ultraviolet (EUV) radiation. Furthermore, EUV and longer wavelength UV radiation power disequilibrium chemistry in the middle and upper atmosphere. Our understanding of atmospheric escape and chemistry, therefore, depends on our knowledge of the stellar UV fluxes. While the far-ultraviolet fluxes can be observed for some stars, most of the EUV range is unobservable due to the lack of a space telescope with EUV capabilities and, for the more distant stars, to interstellar medium absorption. Thus, it becomes essential to have indirect means for inferring EUV fluxes from features observable at other wavelengths. We present here analytic functions for predicting the EUV emission of F, G, K, and M-type stars from the log R'HK activity parameter that is commonly obtained from ground-based optical observations of the Ca II H&K lines. The scaling relations are based on a collection of about 100 nearby stars with published log R'HK and EUV flux values, where the latter are either direct measurements or inferences from high-quality far-ultraviolet (FUV) spectra. The scaling relations presented here return EUV flux values with an accuracy of about three, which is slightly lower than that of other similar methods based on FUV or X-ray measurements.
- ID:
- ivo://CDS.VizieR/J/MNRAS/434/1681
- Title:
- Extremely metal-poor stars CaII triplet
- Short Name:
- J/MNRAS/434/1681
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We extend our previous calibration of the infrared CaII triplet (CaT) as a metallicity indicator to the metal-poor regime by including observations of 55 field stars with [Fe/H] down to -4.0dex. While we previously solved the saturation at high metallicity using a combination of a Lorentzian and a Gaussian to reproduce the line profiles, in this paper we address the non-linearity at low metallicity following the suggestion of Starkenburg et al. of adding two non-linear terms to the relation among the [Fe/H], luminosity and strength of the calcium triplet lines. Our calibration thus extends from -4.0 to +0.5 in metallicity and is presented using four different luminosity indicators: V-V_HB_, M_V_, M_I_ and M_K_. The calibration obtained in this paper results in a tight correlation between [Fe/H] abundances measured from high-resolution spectra and [Fe/H] values derived from the CaT, over the whole metallicity range covered.
- ID:
- ivo://CDS.VizieR/J/A+A/522/A79
- Title:
- Faint, high-Galactic-latitude red clump stars
- Short Name:
- J/A+A/522/A79
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- With this survey we aim to derive accurate, multi-epoch radial velocities and atmospheric parameters (Teff, logg, [M/H] and V_rot_sini) of a large sample of carefully selected red clump (RC) stars located over a great circle at high Galactic latitudes. We acquired data of the program stars of high signal-to-noise ratio and high resolution with the Asiago Echelle spectrograph. We obtained radial velocities by applying cross-correlation and atmospheric parameters via chi2 fitting to a synthetic spectral library. Extensive tests were carried out by re-observing with the same instrument a large number of standard stars taken from a variety of sources in literature.
- ID:
- ivo://CDS.VizieR/J/A+A/527/A40
- Title:
- Faint, high-Galactic-latitude red clump stars
- Short Name:
- J/A+A/527/A40
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The goal of our survey is to provide accurate and multi-epoch radial velocities, atmospheric parameters (Teff, logg and [M/H]), distances, and space velocities of faint red clump (RC) stars. We recorded high signal-to-noise (S/N>=200) spectra of RC stars over the 4750-5950{AA} range at a resolving power 5500. The target stars are distributed across the great circle of the celestial equator. Radial velocities were obtained via cross-correlation with IAU radial velocity standards. Atmospheric parameters were derived via {chi}^2^ fit to a synthetic spectral library. A large number of RC stars from other surveys were re-observed to check the consistency of our results and the absence of offsets and trends.
