- ID:
- ivo://CDS.VizieR/J/A+A/402/343
- Title:
- IR O I triplet, [O I] lines in F-K dwarfs/giants
- Short Name:
- J/A+A/402/343
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In order to investigate the formation of O I 7771-5 and [O I] 6300/6363 lines, extensive non-LTE calculations for neutral atomic oxygen were carried out for wide ranges of model atmosphere parameters, which are applicable to early-K through late-F halo/disk stars of various evolutionary stages. The formation of the triplet O I lines was found to be well described by the classical two-level-atom scattering model, and the non-LTE correction is practically determined by the parameters of the line-transition itself without any significant relevance to the details of the oxygen atomic model. This simplifies the problem in the sense that the non-LTE abundance correction is essentially determined only by the line-strength (W_{lambda}_), if the atmospheric parameters of Teff, logg, and {xi} are given, without any explicit dependence of the metallicity; thus allowing a useful analytical formula with tabulated numerical coefficients. On the other hand, our calculations lead to the robust conclusion that LTE is totally valid for the forbidden [O I] lines.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/795/22
- Title:
- Iron abundance of Terzan 5 stars
- Short Name:
- J/ApJ/795/22
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new determinations of the iron abundance for 220 stars belonging to the stellar system Terzan 5 in the Galactic bulge. The spectra have been acquired with FLAMES at the Very Large Telescope of the European Southern Observatory and DEIMOS at the Keck II Telescope. This is by far the largest spectroscopic sample of stars ever observed in this stellar system. From this data set, a subsample of targets with spectra unaffected by TiO bands was extracted and statistically decontaminated from field stars. Once combined with 34 additional stars previously published by our group, a total sample of 135 member stars covering the entire radial extent of the system has been used to determine the metallicity distribution function of Terzan 5. The iron distribution clearly shows three peaks: a super-solar component at [Fe/H]=~0.25 dex, accounting for ~29% of the sample, a dominant sub-solar population at [Fe/H]=~-0.30 dex, corresponding to ~62% of the total, and a minor (6%) metal-poor component at [Fe/H]=~-0.8 dex. Such a broad, multi-modal metallicity distribution demonstrates that Terzan 5 is not a genuine globular cluster but the remnant of a much more complex stellar system.
- ID:
- ivo://CDS.VizieR/J/A+A/566/A37
- Title:
- Iron abundances for 42 Galactic Cepheids
- Short Name:
- J/A+A/566/A37
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present homogeneous and accurate iron abundances for 42 Galactic Cepheids based on high resolution (R~38000) high signal-to-noise ratio (S/N>=100) optical spectra collected with UVES at VLT (128 spectra). The above abundances were complemented with high-quality iron abundances provided either by our group (86) or available in the literature. We were careful to derive a common metallicity scale and ended up with a sample of 450 Cepheids. We also estimated accurate individual distances for the entire sample by using homogeneous near-infrared photometry and the reddening free period-Wesenheit relations. The new metallicity gradient is linear over a broad range of Galactocentric distances (R_G_~5-19kpc) and agrees quite well with similar estimates available in the literature (-0.060+/-0.002dex/kpc). We also uncover evidence that suggests that the residuals of the metallicity gradient are tightly correlated with candidate Cepheid groups (CGs). The candidate CGs have been identified as spatial overdensities of Cepheids located across the thin disk. They account for a significant fraction of the residual fluctuations, and also for the large intrinsic dispersion of the metallicity gradient. We performed a detailed comparison with metallicity gradients based on different tracers: OB stars and open clusters. We found very similar metallicity gradients for ages younger than 3Gyr, while for older ages we found a shallower slope and an increase in the intrinsic spread. The above findings rely on homogeneous age, metallicity, and distance scales. Finally, by using a large sample of Galactic and Magellanic Cepheids for which accurate iron abundances are available, we found that the dependence of the luminosity amplitude on metallicity is vanishing.
- ID:
- ivo://CDS.VizieR/J/PASP/124/519
- Title:
- Iron abundances of red giants in Carina gal.
- Short Name:
- J/PASP/124/519
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have performed accurate iron abundance measurements for 44 red giants (RGs) in the Carina dwarf spheroidal (dSph) galaxy. We used archival, high-resolution spectra (R~38000) collected with UVES at ESO/VLT either in slit mode (five RGs) or in fiber mode (39 RGs, FLAMES/GIRAFFE-UVES). The sample is more than a factor of 4 larger than any previous spectroscopic investigation of stars in dSphs based on high-resolution (R>=38000) spectra.
- ID:
- ivo://CDS.VizieR/J/ApJ/790/73
- Title:
- Iron and alpha abundance of RGBs in M31 satellites
- Short Name:
- J/ApJ/790/73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present alpha to iron abundance ratios for 226 individual red giant branch stars in nine dwarf galaxies of the Andromeda (M31) satellite system. The abundances are measured from the combined signal of Mg, Si, Ca, and Ti lines in Keck/DEIMOS medium-resolution spectra. This constitutes the first large sample of alpha abundance ratios measured in the M31 satellite system. The dwarf galaxies in our sample exhibit a variety of alpha abundance ratios, with the average values in each galaxy ranging from approximately solar ([{alpha}/Fe] ~ + 0.0) to alpha-enhanced ([{alpha}/Fe] ~ + 0.5). These variations do not show a correlation with internal kinematics, environment, or stellar density. We confirm radial gradients in the iron abundance of two galaxies out of the five with sufficient data (NGC 185 and And II). There is only tentative evidence for an alpha abundance radial gradient in NGC 185. We homogeneously compare our results to the Milky Way classical dwarf spheroidals, finding evidence for wider variation in average alpha abundance. In the absence of chemical abundances for the M31 stellar halo, we compare to the Milky Way stellar halo. A stellar halo comprised of disrupted M31 satellites is too metal-rich and inconsistent with the Milky Way halo alpha abundance distribution even if considering only satellites with predominantly old stellar populations. The M31 satellite population provides a second system in which to study chemical abundances of dwarf galaxies and reveals a wider variety of abundance patterns than the Milky Way.
- ID:
- ivo://CDS.VizieR/J/ApJ/890/119
- Title:
- Iron element abundances in 3 very metal-poor stars
- Short Name:
- J/ApJ/890/119
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained new detailed abundances of the Fe-group elements Sc through Zn (Z=21-30) in three very metal-poor ([Fe/H]~-3) stars: BD+03 740, BD-13 3442, and CD-33 1173. High-resolution ultraviolet Hubble Space Telescope/Space Telescope Imaging Spectrograph spectra in the wavelength range 2300-3050{AA} were gathered, and complemented by an assortment of optical echelle spectra. The analysis featured recent laboratory atomic data for a number of neutral and ionized species for all Fe-group elements except Cu and Zn. A detailed examination of scandium, titanium, and vanadium abundances in large-sample spectroscopic surveys indicates that they are positively correlated in stars with [Fe/H]<=-2. The abundances of these elements in BD+03 740, BD-13 3442, CD-33 1173, and HD 84937 (studied in a previous paper of this series) are in accord with these trends and lie at the high end of the correlations. Six elements have detectable neutral and ionized features, and generally their abundances are in reasonable agreement. For Cr we find only minimal abundance disagreement between the neutral (mean of [CrI/Fe]=+0.01) and ionized species (mean of [CrII/Fe]=+0.08), unlike most studies in the past. The prominent exception is Co, for which the neutral species indicates a significant overabundance (mean of [CoI/H]=-2.53), while no such enhancement is seen for the ionized species (mean of [CoII/H]=-2.93). These new stellar abundances, especially the correlations among Sc, Ti, and V, suggest that models of element production in early high-mass metal-poor stars should be revisited.
- ID:
- ivo://CDS.VizieR/J/ApJ/801/69
- Title:
- Iron EWs for 21 giant star members of NGC3201
- Short Name:
- J/ApJ/801/69
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NGC 3201 is a globular cluster suspected to have an intrinsic spread in the iron content. We re-analyzed a sample of 21 cluster stars observed with UVES-FLAMES at the Very Large Telescope and for which Simmerer et al. (2013ApJ...764L...7S) found a 0.4dex wide [Fe/H] distribution with a metal-poor tail. We confirmed that when spectroscopic gravities are adopted, the derived [Fe/H] distribution spans ~0.4dex. On the other hand, when photometric gravities are used, the metallicity distribution from Fe I lines remains large, while that derived from Fe II lines is narrow and compatible with no iron spread. We demonstrate that the metal-poor component claimed by Simmerer et al. (2013ApJ...764L...7S) is composed by asymptotic giant branch stars that could be affected by non-local thermodynamical equilibrium effects driven by iron overionization. This leads to a decrease of the Fe I abundance, while leaving the Fe II abundance unaltered. A similar finding has been already found in asymptotic giant branch stars of the globular clusters M5 and 47 Tucanae. We conclude that NGC 3201 is a normal cluster, with no evidence of intrinsic iron spread.
- ID:
- ivo://CDS.VizieR/J/A+A/600/A22
- Title:
- Iron-peak elements in solar neighbourhood
- Short Name:
- J/A+A/600/A22
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The aim of this paper is to characterise the abundance patterns of five iron-peak elements (Mn, Fe, Ni, Cu, and Zn) for which the stellar origin and chemical evolution are still debated. We automatically derived iron peak (Mn, Fe, Ni, Cu, and Zn) and alpha element (Mg) chemical abundances for 4666 stars. We used the bimodal distribution of [Mg/Fe] to chemically classify sample stars into different Galactic substructures: thin disc, metal-poor and high-alpha metal rich, high-alpha and low-alpha metal-poor populations. High-alpha and low-alpha metal-poor populations are fully distinct in Mg, Cu, and Zn. Thin disc trends of [Ni/Fe] and [Cu/Fe] are very similar and show a small increase at supersolar metallicities. Thin and thick disc trends of Ni and Cu are very similar and indistinguishable. Mn looks different from Ni and Cu. [Mn/Fe] trends of thin and thick discs actually have noticeable differences: the thin disc is slightly Mn richer than the thick disc. [Zn/Fe] trends look very similar to those of [alpha/Fe] trends. The dispersion of results in both discs is low (~0.05dex for [Mg, Mn, and Cu/Fe]) and is even much lower for [Ni/Fe] (~0.035dex). Zn is an alpha-like element and could be used to separate thin and thick disc stars. [Mn/Mg] ratio could also be a very good tool for tagging Galactic substructures. Some models can partially reproduce the observed Mg, Zn, and, Cu behaviours. Models mostly fail to reproduce Mn and Ni in all metallicity domains, however, models adopting yields normalised from solar chemical properties reproduce Mn and Ni better, suggesting that there is still a lack of realistic theoretical yields of some iron-peak elements. Very low scatter (~0.05dex) in thin and thick disc sequences could provide an observational constrain for Galactic evolutionary models that study the efficiency of stellar radial migration.
- ID:
- ivo://CDS.VizieR/J/AJ/158/105
- Title:
- IR photometry of field RR Lyrae variable stars
- Short Name:
- J/AJ/158/105
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present multi-epoch infrared photometry in the K_s_-band for 74 bright RR Lyrae variable stars tied directly to the Two-Micron All-Sky Survey (2MASS) photometric system. We systematize additional K-band photometry from the literature to the 2MASS system and combine it to obtain photometry for 146 RR Lyrae stars on a consistent, modern system. A set of outlier stars in the literature photometry is identified and discussed. Reddening estimates for each star are gathered from the literature and combined to provide an estimate of the interstellar absorption affecting each star, and we find excellent agreement with another source in the literature. We utilize trigonometric parallaxes from the Second Data Release of the European Space Agency's Gaia astrometric satellite to determine the absolute magnitude, M_Ks_ for each of these stars, and analyze them using the astrometry-based luminosity prescription to obtain a parallax-based calibration of M_K_ (RR). Our period-luminosity-metallicity relationship is M_Ks_=(-2.8+/-0.2)(logP+0.27)+(0.12+/-0.02) ([Fe/H]+1.3)-(0.41+/-0.03) mag. A Gaia global zero-point error of {pi}_zp_=-0.042+/-0.013 mas is determined for this sample of RR Lyrae stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/566/880
- Title:
- ISO-SWS observations of H II regions
- Short Name:
- J/ApJ/566/880
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present mid-infrared Infrared Space Observatory Short-Wavelength Spectrometer (ISO-SWS) observations of the fine-structure emissions lines [Ne II] 12.8{mu}m, [Ne III] 15.6{mu}m, [Ne III] 36.0{mu}m, [Ar II] 6.99{mu}m, [Ar III] 8.99{mu}m, [S III] 18.7{mu}m, [S III] 33.5{mu}m, and [S IV] 10.5{mu}m and the recombination lines Br{alpha} and Br{beta} n a sample of 112 Galactic H II regions and 37 nearby extra-Galactic H II regions in the LMC, SMC, and M33.
