- ID:
- ivo://CDS.VizieR/J/MNRAS/418/863
- Title:
- NLTE corrections for Mg and Ca lines
- Short Name:
- J/MNRAS/418/863
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate NLTE effects for magnesium and calcium in the atmospheres of late-type giant and supergiant stars. The aim of this paper is to provide a grid of NLTE/LTE equivalent width ratios W/W* of Mg and Ca lines for the following range of stellar parameters: Teff in [3500,5250]K, log(g) in [0.5,2.0]dex and [Fe/H] in [-4.0,0.5]dex. We use realistic model atoms with the best physics available and taking into account the fine structure. The Mg and Ca lines of interest are in optical and near IR ranges. A special interest concerns the lines in the Gaia spectrograph (RVS) wavelength domain [847,874]nm. The NLTE corrections are provided as function of stellar parameters in an electronic table as well as in a polynomial form for the Gaia/RVS lines.
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- ID:
- ivo://CDS.VizieR/J/A+A/541/A143
- Title:
- NLTE Corrections of the Ca lines
- Short Name:
- J/A+A/541/A143
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Extremely metal-poor stars contain the fossil records of the chemical composition of the early Galaxy and it is important to compare Ca abundance with abundances of other light elements, that are supposed to be synthesized in the same stellar evolution phases. The NLTE profiles of the calcium lines were computed with a modified version of the program MULTI, which allows a very good description of the radiation field.
- ID:
- ivo://CDS.VizieR/J/ApJ/847/16
- Title:
- NLTE spectroscopy. II. Galactic metal-poor stars
- Short Name:
- J/ApJ/847/16
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- From exploratory studies and theoretical expectations it is known that simplifying approximations in spectroscopic analysis (local thermodynamic equilibrium (LTE), 1D) lead to systematic biases of stellar parameters and abundances. These biases depend strongly on surface gravity, temperature and, in particular, for LTE versus non-LTE (NLTE), on metallicity of the stars. Here we analyze the [Mg/Fe] and [Fe/H] plane of a sample of 326 stars, comparing LTE and NLTE results obtained using 1D hydrostatic models and averaged <3D> models. We show that compared to the <3D> NLTE benchmark, the other three methods display increasing biases toward lower metallicities, resulting in false trends of [Mg/Fe] against [Fe/H], which have profound implications for interpretations by chemical evolution models. In our best <3D> NLTE model, the halo and disk stars show a clearer behavior in the [Mg/Fe]-[Fe/H] plane, from the knee in abundance space down to the lowest metallicities. Our sample has a large fraction of thick disk stars and this population extends down to at least [Fe/H]~-1.6dex, further than previously proven. The thick disk stars display a constant [Mg/Fe]~0.3dex, with a small intrinsic dispersion in [Mg/Fe] that suggests that a fast SN Ia channel is not relevant for the disk formation. The halo stars reach higher [Mg/Fe] ratios and display a net trend of [Mg/Fe] at low metallicities, paired with a large dispersion in [Mg/Fe]. These indicate the diverse origin of halo stars from accreted low-mass systems to stochastic/inhomogeneous chemical evolution in the Galactic halo.
- ID:
- ivo://CDS.VizieR/J/ApJ/864/144
- Title:
- N/O and Ne/O ratios of SDSS dwarf galaxies
- Short Name:
- J/ApJ/864/144
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study how the void environment affects the chemical evolution of galaxies in the universe by comparing the oxygen and nitrogen abundances of dwarf galaxies in voids with dwarf galaxies in denser regions. Using spectroscopic observations from the Sloan Digital Sky Survey Data Release 7, we estimate the oxygen, nitrogen, and neon abundances of 889 void dwarf galaxies and 672 dwarf galaxies in denser regions. We use the Direct T_e_ method for calculating the gas-phase chemical abundances in the dwarf galaxies because it is best suited for low-metallicity, low-mass (dwarf) galaxies. A substitute for the [OII]{lambda}3727 doublet is developed, permitting oxygen abundance estimates of SDSS dwarf galaxies at all redshifts with the Direct T_e_ method. We find that void dwarf galaxies have about the same oxygen abundance and Ne/O ratio as dwarf galaxies in denser environments. However, we find that void dwarf galaxies have slightly higher neon (~10%) abundances than dwarf galaxies in denser environments. The opposite trend is seen in both the nitrogen abundance and N/O ratio: void dwarf galaxies have slightly lower nitrogen abundances (~5%) and lower N/O ratios (~7%) than dwarf galaxies in denser regions. Therefore, we conclude that the void environment has a slight influence on dwarf galaxy chemical evolution. Our mass-N/O relationship shows that the secondary production of nitrogen commences at a lower stellar mass in void dwarf star-forming galaxies than in dwarf star-forming galaxies in denser environments. We also find that star-forming void dwarf galaxies have higher HI masses than the star-forming dwarf galaxies in denser regions. Our star-forming dwarf galaxy sample demonstrates a strong anti-correlation between the sSFR and N/O ratio, providing evidence that oxygen is produced in higher-mass stars than those which synthesize nitrogen. The lower N/O ratios and smaller stellar mass for secondary nitrogen production seen in void dwarf galaxies may indicate both delayed star formation as predicted by {Lambda}CDM cosmology and a dependence of cosmic downsizing on the large-scale environment. A shift toward slightly higher oxygen abundances and higher HI masses in void dwarf galaxies could be evidence of larger ratios of dark matter halo mass to stellar mass in voids compared with denser regions.
- ID:
- ivo://CDS.VizieR/J/A+A/627/A177
- Title:
- Non-LTE analysis of K I in late-type stars
- Short Name:
- J/A+A/627/A177
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Older models of Galactic chemical evolution (GCE) predict [K/Fe] ratios as much as 1dex lower than those inferred from stellar observations. Abundances of potassium are mainly based on analyses of the 7698{AA} resonance line, and the discrepancy between GCE models and observations is in part caused by the assumption of local thermodynamic equilibrium (LTE) in spectroscopic analyses. We study the statistical equilibrium of KI, focusing on the non-LTE effects on the 7698{AA} line. We aim to determine how non-LTE abundances of potassium can improve the analysis of its chemical evolution, and help to constrain the yields of GCE models. We construct a new model KI atom that employs the most up-to-date atomic data. In particular, we calculate and present inelastic e+K collisional excitation cross-sections from the convergent close-coupling (CCC) and the B-Spline R-matrix (BSR) methods, and H+K collisions from the two-electron model (LCAO). We constructed a fine, extended grid of non-LTE abundance corrections based on 1D MARCS models that span 4000<Teff/=K<8000, 0.50<logg<5.00, -5.00<[Fe/H]<+0.50, and applied the corrections to potassium abundances extracted from the literature.
- ID:
- ivo://CDS.VizieR/J/A+A/373/987
- Title:
- Non-LTE Ga abundance in HgMn stars
- Short Name:
- J/A+A/373/987
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present, for the first time, the Non-LTE gallium equivalent widths for the most prominent gallium transitions as identified in real spectra and in (hot) mercury-manganese star. The common feature of the departure coefficients is to decrease near the stellar surface, the collision rates are dominant in many cases and the Non-LTE equivalent widths are generally smaller. In particular, the abundance difference as derived from UV and visual lines is reduced. The photoionization cross sections were computed by means of standard R-matrix formalism.
- ID:
- ivo://CDS.VizieR/J/A+A/618/A133
- Title:
- Non standard s-process in massive rotating stars
- Short Name:
- J/A+A/618/A133
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent studies show that rotation significantly affects the s-process in massive stars. We provide tables of yields for non-rotating and rotating massive stars between 10 and 150M_{sun}_ at Z=10^-3^([Fe/H]=-1.8). Tables for different mass cuts are provided. The complete s-process is followed during the whole evolution with a network of 737 isotopes, from Hydrogen to Polonium. A grid of stellar models with initial masses of 10, 15, 20, 25, 40, 60, 85, 120 and 150M_{sun}_ and with an initial rotation rate of both 0 or 40% of the critical velocity was computed. Three extra models were computed in order to investigate the effect of faster rotation (70% of the critical velocity) and of a lower ^17^O({alpha},{gamma}) reaction rate. At the considered metallicity, rotation has a strong impact on the production of s-elements for initial masses between 20 and 60M_{sun}_. In this range, the first s-process peak is boosted by 2-3dex if rotation is included. Above 60M_{sun}_, s-element yields of rotating and non-rotating models are similar. Increasing the initial rotation from 40% to 70% of the critical velocity enhances the production of 40<~Z<~60 elements by ~0.5-1dex. Adopting a reasonably lower ^17^O({alpha},{gamma}) rate in the fast rotating model (70% of the critical velocity) boosts again the yields of s-elements with 55<~Z<~82 by about 1dex. In particular, a modest amount of Pb is produced. Together with s-elements, some light elements (particularly fluorine) are strongly overproduced in rotating models.
- ID:
- ivo://CDS.VizieR/J/ApJ/837/42
- Title:
- N/O ratio of dwarf galaxies from SDSS
- Short Name:
- J/ApJ/837/42
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We examine how the cosmic environment affects the chemical evolution of galaxies in the universe by comparing the N/O ratio of dwarf galaxies in voids with that of dwarf galaxies in denser regions. Ratios of the forbidden [OIII] and [SII] transitions provide estimates of a region's electron temperature and number density. We estimate the abundances of oxygen and nitrogen using these temperature and density estimates and the emission-line fluxes [OII]3727, [OIII]4959,5007, and [NII]6548,6584 with the direct T_e_ method. Using spectroscopic observations from the Sloan Digital Sky Survey Data Release 7, we are able to estimate the N/O ratio in 42 void dwarf galaxies and 89 dwarf galaxies in denser regions. The N/O ratio for void dwarfs (M_r_>-17) is slightly lower (~12%) than for dwarf galaxies in denser regions. We also estimate the nitrogen and oxygen abundances of 2050 void galaxies and 3883 galaxies in denser regions with M_r_>-20. These somewhat brighter galaxies (but still fainter than L_*_) also display similar minor shifts in the N/O ratio. The shifts in the average and median element abundance values in all absolute magnitude bins studied are in the same direction, suggesting that the large-scale environment may influence the chemical evolution of galaxies. We discuss possible causes of such a large-scale environmental dependence of the chemical evolution of galaxies, including retarded star formation and a higher ratio of dark matter halo mass to stellar mass in void galaxies.
- ID:
- ivo://CDS.VizieR/J/A+A/576/A94
- Title:
- Northern bright planet host stars parameters
- Short Name:
- J/A+A/576/A94
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work we derive new precise and homogeneous parameters for 37 stars with planets. For this purpose, we analyze high resolution spectra obtained by the NARVAL spectrograph for a sample composed of bright planet host stars in the northern hemisphere. The new parameters are included in the SWEET-Cat online catalogue. To ensure that the catalogue is homogeneous, we use our standard spectroscopic analysis procedure, ARES + MOOG, to derive effective temperatures, surface gravities, and metallicities. These spectroscopic stellar parameters are then used as input to compute the stellar mass and radius, which are fundamental for the derivation of the planetary mass and radius.
- ID:
- ivo://CDS.VizieR/J/ApJ/891/28
- Title:
- N-rich field stars from LAMOST and APOGEE data
- Short Name:
- J/ApJ/891/28
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Interesting chemically peculiar field stars may reflect their stellar evolution history and their possible origin in a different environment from where they are found now; this is one of the most important research fields in Galactic archeology. To explore this further, we have used the CN-CH bands around 4000{AA} to identify N-rich metal-poor field stars in LAMOST DR3. Here we expand our N-rich, metal-poor field star sample to ~100 stars in LAMOST DR5, where 53 of them are newly found in this work. We investigate light elements of common stars between our sample and APOGEE DR14. While Mg, Al, and Si abundances generally agree with the hypothesis that N-rich metal-poor field stars come from enriched populations in globular clusters, it is still inconclusive for C, N, and O. After integrating the orbits of our N-rich field stars and a control sample of normal metal-poor field stars, we find that N-rich field stars have different orbital parameter distributions compared to the control sample-specifically, apocentric distances, maximum vertical amplitude (Zmax), orbital energy, and z-direction angular momentum (Lz). The orbital parameters of N-rich field stars indicate that most of them are inner-halo stars. The kinematics of N-rich field stars support their possible GC origin. The spatial and velocity distributions of our bona fide N-rich field star sample are important observational evidence to constrain simulations of the origin of these interesting objects.
