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- ID:
- ivo://CDS.VizieR/J/MNRAS/468/L113
- Title:
- Nitrogen abundance of Seyfert 2 AGN
- Short Name:
- J/MNRAS/468/L113
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We obtained new quantitative determinations of the nitrogen abundance and a consistent relation between the nitrogen and oxygen abundances for a sample of Seyfert 2 galaxies located at redshift z<0.1. We carried out this analysis using the CLOUDY code to build detailed photoionization models. We were able to reproduce observed optical narrow emission line intensities for 44 sources compiled from the literature. Our results show that Seyfert 2 nuclei have nitrogen abundances ranging from ~0.3 to ~7.5 times the solar value. We derived the relation log (N/H)=1.05(+/-0.09)x[log(O/H)]-0.35(+/-0.33). Results for N/O versus O/H abundance ratios derived for Seyfert 2 galaxies are in consonance with those recently derived for a sample of extragalactic disc HII regions with high metallicity.
- ID:
- ivo://CDS.VizieR/J/MNRAS/471/3398
- Title:
- Nitrogen abundances for Be and B stars
- Short Name:
- J/MNRAS/471/3398
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Photospheric nitrogen abundances for a sample of 26 Be stars and 16 normal B stars were found using high-resolution spectra from the Magnetism in Massive Stars (MiMeS) spectroscopic survey. Nitrogen abundances were obtained using non-local-thermodynamic-equilibrium equivalent widths and line profiles, and Monte Carlo simulation was used to determine the error bounds of the measured nitrogen abundances due to uncertainties in the adopted stellar parameters, continuum normalization and atomic data. In addition, the effects of gravitational darkening and disc contamination on the measured Be star nitrogen abundances were investigated. About one third of the sample of Be stars and half of the normal B-type stars have nitrogen enrichment that may be due to rotational mixing in these rapidly rotating objects. Corrections for gravitational darkening and disc contamination do not significantly change the overall results for the Be star sample. The average nitrogen abundance of the B and Be star samples coincides with the solar abundance, although the dispersion in the nitrogen abundances is much larger in the Be star sample. The Be star sample also has a significant fraction of sub-solar nitrogen abundance objects that are not present in significant numbers in the B star sample. This may point to yet unresolved systematic errors in the analysis of the Be stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/658/1203
- Title:
- Nitrogen-enhanced metal-poor stars
- Short Name:
- J/ApJ/658/1203
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Theoretical models of very metal-poor intermediate-mass asymptotic giant branch (AGB) stars predict a large overabundance of primary nitrogen. The very metal-poor, carbon-enhanced, s-process-rich stars, which are thought to be the polluted companions of now extinct AGB stars, provide direct tests of the predictions of these models. Recent studies of the carbon and nitrogen abundances in metal-poor stars have focused on the most carbon-rich stars, leading to a potential selection bias against stars that have been polluted by AGB stars that produced large amounts of nitrogen and hence have small [C/N] ratios. We call these stars nitrogen-enhanced metal-poor (NEMP) stars and define them as having [N/Fe]>+0.5 and [C/N]<-0.5. In this paper we report on the [C/N] abundances of a sample of 21 carbon-enhanced stars, all but three of which have [C/Fe]<+2.0. If NEMP stars were made as easily as carbon-enhanced metal-poor (CEMP) stars, then we expected to find between two and seven NEMP stars. Instead, we found no NEMP stars in our sample.
- 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/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.
