- ID:
- ivo://CDS.VizieR/J/A+A/425/263
- Title:
- Spectroscopic atlas of HD175640
- Short Name:
- J/A+A/425/263
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a high resolution spectral atlas of the HgMn star HD 175640 covering the 3040-10000{AA} region. UVES spectra observed with 90000-110000 resolving power and signal to noise ratio ranging from 200 to 400 are compared with a synthetic spectrum computed with the SYNTHE code (Kurucz, 1993, CD-ROM, No. 18). The model atmosphere is an ATLAS12 model (Kurucz, 1997, in The 3rd Conf. on Faint Blue Stars, ed. Philip, Liebert & Saffer (Schenectady: L. Davis Press), 33) with parameters Teff=12000K,logg=3.95, vturb=0km/s. The stellar individual abundances in ATLAS12 were derived from an iterative procedure. The starting atomic line lists downloaded from the Kurucz website have been improved and extended by examining different sources in the literature and by comparing the computed profiles with the observed spectrum. The high quality of the data allowed us to study the isotopic and hyperfine structure for several lines of Mn II, Ga II, Ba II, Pt II, Hg I, and Hg II. Numerous weak emission lines from Cr II and Ti II have been identified in the red part of the spectrum, starting at about 5847{AA}. Two emission lines of C I (mult. 10, mult. 9) have been observed for the first time. All Cr II and Ti II emission lines originate from the high excitation states (Elow>89000cm^-1^ for Cr II and Elow>62000cm^-1^ for Ti II) with large transition probabilities (loggf>-1.00). The synthetic spectrum superimposed on the observed spectrum are available at http://wwwuser.oat.ts.astro.it/castelli/stars.html . An extended discussion on each identified ion and related atomic data is available both in the quoted website and in an electronic Appendix to the paper.
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- ID:
- ivo://CDS.VizieR/J/AJ/117/2308
- Title:
- Spectroscopy of hot stars in the halo
- Short Name:
- J/AJ/117/2308
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We discuss a spectroscopic and photometric technique that enables the identification and classification of field horizontal-branch (FHB) and other A-type stars, even from relatively low signal-to-noise ratio medium-resolution spectra. This technique makes use of broadband UBV colors predicted from model atmosphere calculations and Balmer line profiles and Ca II K equivalent widths determined from synthetic spectra to estimate the physical parameters T_eff_, log(g), and [Fe/H] for stars in the effective temperature range 6000 - 10,000 K.
- ID:
- ivo://CDS.VizieR/J/MNRAS/361/1102
- Title:
- Spectrum of {epsilon} Eri
- Short Name:
- J/MNRAS/361/1102
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Measurements of ultraviolet line fluxes from Space Telescope Imaging Spectrograph and Far-Ultraviolet Spectroscopic Explorer spectra of the K2-dwarf eps Eri are reported. These are used to develop new emission measure distributions and semi-empirical atmospheric models for the chromosphere and lower transition region of the star. These models are the most detailed constructed to date for a main-sequence star other than the Sun. New ionization balance calculations, which account for the effect of finite density on dielectronic recombination rates, are presented for carbon, nitrogen, oxygen and silicon. The results of these calculations are significantly different from the standard Arnaud & Rothenflug ion balance, particularly for alkali-like ions. The new atmospheric models are used to place constraints on possible first ionization potential (FIP)-related abundance variations in the lower atmosphere and to discuss limitations of single-component models for the interpretation of certain optically thick line fluxes.
- ID:
- ivo://CDS.VizieR/J/A+A/557/A26
- Title:
- STAGGER-grid of 3D stellar models. I.
- Short Name:
- J/A+A/557/A26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the STAGGER-grid, a comprehensive grid of time-dependent, three-dimensional (3D), hydrodynamic model atmospheres for late-type stars with realistic treatment of radiative transfer, covering a wide range in stellar parameters. All our models were generated with the Stagger-code, using realistic input physics for the equation of state (EOS) and for continuous and line opacities. Our ~220 grid models range in effective temperature, Teff, from 4000 to 7000K in steps of 500K, in surface gravity, logg, from 1.5 to 5.0 in steps of 0.5dex, and metallicity, [Fe/H], from -4.0 to +0.5 in steps of 0.5 and 1.0dex.
- ID:
- ivo://CDS.VizieR/J/A+A/560/A8
- Title:
- STAGGER-grid of 3D stellar models. II.
- Short Name:
- J/A+A/560/A8
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the implications of averaging methods with different reference depth scales for 3D hydrodynamical model atmospheres computed with the Stagger-code. The temporally and spatially averaged (hereafter denoted as <3D>) models are explored in the light of local thermodynamic equilibrium (LTE) spectral line formation by comparing spectrum calculations using full 3D atmosphere structures with those from <3D> averages. We explored methods for computing mean <3D> stratifications from the Stagger-grid time-dependent 3D radiative hydrodynamical atmosphere models by considering four different reference depth scales (geometrical depth, column-mass density, and two optical depth scales). Furthermore, we investigated the influence of alternative averages (logarithmic, enforced hydrostatic equilibrium, flux-weighted temperatures). For the line formation we computed curves of growth for FeI and FeII lines in LTE.
- ID:
- ivo://CDS.VizieR/J/A+A/573/A89
- Title:
- STAGGER-grid of 3D stellar models. III.
- Short Name:
- J/A+A/573/A89
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the relation between 1D atmosphere models that rely on the mixing length theory and models based on full 3D radiative hydrodynamic (RHD) calculations to describe convection in the envelopes of late-type stars. The adiabatic entropy value of the deep convection zone, s_bot_, and the entropy jump, {Delta}s, determined from the 3D RHD models, are matched with the mixing length parameter, {alpha}_MLT_, from 1D hydrostatic atmosphere models with identical microphysics (opacities and equation-of-state). We also derive the mass mixing length, {alpha}_m_, and the vertical correlation length of the vertical velocity, C[V_z_,V_z_], directly from the 3D hydrodynamical simulations of stellar subsurface convection.
- ID:
- ivo://CDS.VizieR/J/A+A/573/A90
- Title:
- STAGGER-grid of 3D stellar models. IV.
- Short Name:
- J/A+A/573/A90
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We compute the emergent stellar spectra from the UV to far infrared for different viewing angles using realistic 3D model atmospheres for a large range in stellar parameters to predict the stellar limb darkening. We have computed full 3D LTE synthetic spectra based on 3D radiative hydrodynamic atmosphere models from the Stagger-grid in the ranges: Teff from 4000 to 7000K, logg from 1.5 to 5.0, and [Fe/H], from -4.0 to +0.5. From the resulting intensities at different wavelength, we derived coefficients for the standard limb darkening laws considering a number of often-used photometric filters. Furthermore, we calculated theoretical transit light curves, in order to quantify the differences between predictions by the widely used 1D model atmosphere and our 3D models.
- ID:
- ivo://CDS.VizieR/J/A+A/611/A11
- Title:
- STAGGER-grid of 3D stellar models. V.
- Short Name:
- J/A+A/611/A11
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have calculated spectra from 1000 to 200000{AA} with a constant resolving power of {lambda}/{Delta}{lambda}=20000 and from 8470 and 8710{AA} (Gaia Radial Velocity Spectrometer - RVS - spectral range) with a constant resolving power of {lambda}/{Delta}{lambda}=300000. This for the Stagger-grid 3D stellar atmosphere models in the ranges: Teff from 4000 to 7000K, logg from 1.5 to 5.0, and [Fe/H], from -4.0 to +0.5. We used synthetic spectra to compute theoretical colours in the Johnson-Cousins UBV(RI)C, SDSS, 2MASS, Gaia, SkyMap- per, Stroemgren systems, and HST-WFC3.
- ID:
- ivo://CDS.VizieR/J/A+A/510/A21
- Title:
- Stellar Limb-Darkening Coefficients
- Short Name:
- J/A+A/510/A21
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Transiting exoplanets provide unparalleled access to the fundamental parameters of both extrasolar planets and their host stars. We present limb-darkening coefficients (LDCs) for the exoplanet hunting CoRot and Kepler missions. The LDCs are calculated with ATLAS stellar atmospheric model grids and span a wide range of T_eff_, logg, and metallically [M/H]. Both CoRot and Kepler use wide nonstandard photometric filters, and are producing a large inventory of high- quality transiting lightcurves, sensitive to stellar limb darkening. Comparing the stellar model limb darkening to results from the first seven CoRot planets, we find better fits are found when two model intensities at the limb are excluded in the coefficient calculations. This calculation method can help to avoid a major deficiency present at the limbs of the 1D stellar models.
- 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.
