- ID:
- ivo://CDS.VizieR/J/MNRAS/435/952
- Title:
- Lick indices for 51 stars
- Short Name:
- J/MNRAS/435/952
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A method that is widely used to analyse stellar populations in galaxies is to apply the theoretically derived responses of stellar spectra and line indices to element abundance variations, which are hereafter referred to as response functions. These are applied in a differential way, to base models, in order to generate spectra or indices with different abundance patterns. In this paper, sets of such response functions for three different stellar evolutionary stages are tested with new empirical [Mg/Fe] abundance data for the medium-resolution Isaac Newton Telescope library of empirical spectra (MILES). Recent theoretical models and observations are used to investigate the effects of [Fe/H], [Mg/H] and overall [Z/H] on spectra, via ratios of spectra for similar stars. The global effects of changes in abundance patterns are investigated empirically through direct comparisons of similar stars from MILES, highlighting the impact of abundance effects in the blue part of the spectrum, particularly for lower temperature stars. It is found that the relative behaviour of iron-sensitive line indices are generally well predicted by response functions, whereas Balmer line indices are not. Other indices tend to show large scatter about the predicted mean relations. Implications for element abundance and age studies in stellar populations are discussed and ways forward are suggested to improve the match with the behaviour of spectra and line-strength indices observed in real stars.
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- ID:
- ivo://CDS.VizieR/J/AJ/143/14
- Title:
- Lick indices of M31 globular clusters
- Short Name:
- J/AJ/143/14
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present absorption line indices measured in the integrated spectra of globular clusters both from the Galaxy and from M31. Our samples include 41 Galactic globular clusters, and more than 300 clusters in M31. The conversion of instrumental equivalent widths into the Lick system is described, and zero-point uncertainties are provided. Comparison of line indices of old M31 clusters and Galactic globular clusters suggests an absence of important differences in chemical composition between the two cluster systems. In particular, CN indices in the spectra of M31 and Galactic clusters are essentially consistent with each other, in disagreement with several previous works. We reanalyze some of the previous data, and conclude that reported CN differences between M31 and Galactic clusters were mostly due to data calibration uncertainties. Our data support the conclusion that the chemical compositions of Milky Way and M31 globular clusters are not substantially different, and that there is no need to resort to enhanced nitrogen abundances to account for the optical spectra of M31 globular clusters.
- ID:
- ivo://CDS.VizieR/J/A+A/610/A38
- Title:
- Li enrichment histories of the thick/thin disc
- Short Name:
- J/A+A/610/A38
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Lithium abundance in most of the warm metal-poor main sequence stars shows a constant plateau (A(Li)~2.2dex) and then the upper envelope of the lithium vs. metallicity distribution increases as we approach solar metallicity. Meteorites, which carry information about the chemical composition of the interstellar medium at the solar system formation time, show a lithium abundance A(Li)~3.26dex. This pattern reflects the Li enrichment history of the interstellar medium during the Galaxy lifetime. After the initial Li production in Big Bang Nucleosynthesis, the sources of the enrichment include AGB stars, low-mass red giants, novae, type II supernovae, and Galactic cosmic rays. The total amount of enriched Li is sensitive to the relative contribution of these sources. Thus different Li enrichment histories are expected in the Galactic thick and thin disc. We investigate the main sequence stars observed with UVES in Gaia-ESO Survey iDR4 catalog and find a Li-[alpha/Fe] anticorrelation independent of [Fe/H], Teff, and log(g). Since in stellar evolution different {alpha} enhancements at the same metallicity do not lead to a measurable Li abundance change, the anticorrelation indicates that more Li is produced during the Galactic thin disc phase than during the Galactic thick disc phase. We also find a correlation between the abundance of Li and s-process elements Ba and Y, and they both decrease above the solar metallicity, which can be explained in the framework of the adopted Galactic chemical evolution models.
- ID:
- ivo://CDS.VizieR/J/AJ/156/6
- Title:
- Light element abundances of RGB & AGB stars in M10
- Short Name:
- J/AJ/156/6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present CN and CH band measurements for 137 red giant branch (RGB) and asymptotic giant branch (AGB) stars in the Galactic globular cluster M10. Our measurements come from low-resolution spectroscopy taken with the Hydra spectrograph on the WIYN-3.5 m telescope. We use these measurements to identify two populations of stars within the cluster, CN-normal and CN-enhanced, and find that in our sample 60% of stars are CN-enhanced. Our large sample allows us to conduct a detailed analysis on the carbon and nitrogen abundances and the radial distribution of each population separately. Our analysis of the radial dependence shows that each population has the same radial distribution in the cluster, which is likely due to the cluster being dynamically evolved. We also compare our results to other methods of classifying multiple populations in globular clusters such as the Na-O anti-correlation and the HST pseudo-color-magnitude diagrams. We find that these three methods of identifying multiple populations are in good agreement with each other for M10 and all lead to an estimate of the fraction of second-generation stars approximately equal to 60%. Among AGB stars, when classified by the CN band, there appears to be a lack of second-generation stars when compared to the RGB stars. However, when classified by [N/Fe], we find a similar 60% of AGB stars in the second generation. Finally, we use the measured carbon and nitrogen abundances in RGB stars to study the change of each element with magnitude as stars evolve up the RGB, comparing the results to globular clusters of similar metallicity, M3 and M13.
- ID:
- ivo://CDS.VizieR/J/ApJ/621/673
- Title:
- Line indices for 124 early-type galaxies
- Short Name:
- J/ApJ/621/673
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The aim of this paper is to set constraints on the epochs of early-type galaxy formation through the "archaeology" of the stellar populations in local galaxies. Using our models of absorption-line indices that account for variable abundance ratios, we derive ages, total metallicities, and element ratios of 124 early-type galaxies in high- and low-density environments. The data are analyzed by comparison with mock galaxy samples created through Monte Carlo simulations taking the typical average observational errors into account, in order to eliminate artifacts caused by correlated errors.
- ID:
- ivo://CDS.VizieR/J/MNRAS/403/896
- Title:
- Line intensities of SDSS HII regions
- Short Name:
- J/MNRAS/403/896
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Spectra of high-metallicity [12+log(O/H)>~8.2] HII regions, where oxygen auroral lines are measurable in both the O^+^ and O^++^ zones, have been extracted from the Data Release 6 of the Sloan Digital Sky Survey (SDSS). Our final sample consists of 181 SDSS spectra of HII regions in galaxies in the redshift range from ~0.025 to ~0.17. The t_2,O_-t_3,O_ diagram is examined. In the SDSS HII regions, the electron temperature t_2,O_ is found to have a large scatter at a given value of the electron temperature t_3,O_. The majority of the SDSS HII regions lie below the t_2,O-t3,O_ relation derived for HII regions in nearby galaxies, i.e. the positions of the SDSS HII regions show a systematic shift towards lower t_2,O_ temperatures or/and towards higher t_3,O_ temperatures. The scatter and shift of the SDSS HII regions in the t_2,O_-t_3,O_ diagram can be understood if they are composite nebulae excited by two or more ionizing sources of different temperatures.
- ID:
- ivo://CDS.VizieR/J/MNRAS/448/1314
- Title:
- Line list for seven target PAndAS clusters
- Short Name:
- J/MNRAS/448/1314
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Detailed chemical abundances are presented for seven M31 outer halo globular clusters (with projected distances from M31 greater than 30 kpc), as derived from high-resolution integrated light spectra taken with the Hobby-Eberly Telescope. Five of these clusters were recently discovered in the Pan-Andromeda Archaeological Survey (PAndAS) - this paper presents the first determinations of integrated Fe, Na, Mg, Ca, Ti, Ni, Ba, and Eu abundances for these clusters. Four of the target clusters (PA06, PA53, PA54, and PA56) are metal poor ([Fe/H]< -1.5), {alpha}-enhanced (though they are possibly less {alpha}-enhanced than Milky Way stars at the 1{sigma} level), and show signs of star-to-star Na and Mg variations. The other three globular clusters (H10, H23, and PA17) are more metal rich, with metallicities ranging from [Fe/H]=-1.4 to -0.9. While H23 is chemically similar to Milky Way field stars, Milky Way globular clusters, and other M31 clusters, H10 and PA17, have moderately low [Ca/Fe], compared to Milky Way field stars and clusters. Additionally, PA17's high [Mg/Ca] and [Ba/Eu] ratios are distinct from Milky Way stars, and are in better agreement with the stars and clusters in the Large Magellanic Cloud. None of the clusters studied here can be conclusively linked to any of the identified streams from PAndAS; however, based on their locations, kinematics, metallicities, and detailed abundances, the most metal-rich PAndAS clusters H23 and PA17 may be associated with the progenitor of the Giant Stellar Stream, H10 may be associated with the SW cloud, and PA53 and PA56 may be associated with the eastern cloud.
- ID:
- ivo://CDS.VizieR/J/MNRAS/446/3319
- Title:
- Line list for the NGC 1851 stars
- Short Name:
- J/MNRAS/446/3319
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We measure the C+N+O abundance sum in red giant stars in two Galactic globular clusters, NGC 1851 and NGC 6752. NGC 1851 has a split subgiant branch which could be due to different ages or C+N+O content while NGC 6752 is representative of the least complex globular clusters. For NGC 1851 and NGC 6752, we obtain average values of A(C+N+O)=8.16+/-0.10 ({sigma}=0.34) and 7.62+/-0.02 ({sigma}=0.06), respectively. When taking into account the measurement errors, we find a constant C+N+O abundance sum in NGC 6752. The C+N+O abundance dispersion is only 0.06 dex, and such a result requires that the source of the light element abundance variations does not increase the C+N+O sum in this cluster. For NGC 1851, we confirm a large spread in C+N+O. In this cluster, the anomalous RGB has a higher C+N+O content than the canonical RGB by a factor of 4 (~0.6 dex). This result lends further support to the idea that the two subgiant branches in NGC 1851 are roughly coeval, but with different CNO abundances.
- ID:
- ivo://CDS.VizieR/J/A+A/632/A55
- Title:
- Line list from Pal 13 sample stars
- Short Name:
- J/A+A/632/A55
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- At a Galactocentric distance of 27kpc, Palomar 13 is an old globular cluster (GC) belonging to the outer halo. We present a chemical abundance analysis of this remote system from high-resolution spectra obtained with the Keck/HIRES spectrograph. Owing to the low signal-to-noise ratio of the data, our analysis is based on a coaddition of the spectra of 18 member stars. We are able to determine integrated abundance ratios for 16 species of 14 elements, of {alpha}-elements (Mg, Si, Ca, and Ti), Fe-peak (Sc, Mn, Cr, Ni, Cu, and Zn), and neutron-capture elements (Y and Ba). While the mean Na abundance is found to be slightly enhanced and halo-like, our method does not allow us to probe an abundance spread that would be expected in this light element if multiple populations are present in Pal 13. We find a metal-poor mean metallicity of -1.91+/-0.05 (statistical) +/-0.22 (systematic), confirming that Pal 13 is a typical metal-poor representative of the outer halo. While there are some differences between individual {alpha}-elements, such as halo-like Mg and Si versus the mildly lower Ca and Ti abundances, the mean [{alpha}/Fe] of 0.34+/-0.06 is consistent with the marginally lower {alpha} component of the halo field and GC stars at similar metallicity. We discuss our results in the context of other objects in the outer halo and consider which of these objects were likely accreted. We also discuss the properties of their progenitors. While chemically, Pal 13 is similar to Gaia-Enceladus and some of its GCs, this is not supported by its kinematic properties within the Milky Way system. Moreover, its chemodynamical similarity with NGC 5466, a purported progeny of the Sequoia accretion event, might indicate a common origin in this progenitor. However, the ambiguities in the full abundance space of this comparison emphasize the difficulties in unequivocally labeling a single GC as an accreted object, let alone assigning it to a single progenitor.
- ID:
- ivo://CDS.VizieR/J/A+A/587/A6
- Title:
- Linelist of 14 Galactic post-AGB stars
- Short Name:
- J/A+A/587/A6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper is part of a larger project in which we systematically study the chemical abundances of Galactic and extragalactic post-asymptotic giant branch (post-AGB) stars. The goal at large is to provide improved observational constraints to the models of the complex interplay between the AGB s-process nucleosynthesis and the associated mixing processes. Aims. Lead (Pb) is the final product of the s-process nucleosynthesis and is predicted to have large overabundances with respect to other s-process elements in AGB stars of low metallicities. However, Pb abundance studies of s-process enriched post-AGB stars in the Magellanic Clouds show a discrepancy between observed and predicted Pb abundances. The determined upper limits based on spectral studies are much lower than what is predicted. In this paper, we focus specifically on the Pb abundance of 14 Galactic s-process enhanced post-AGB stars to check whether the same discrepancy is present in the Galaxy as well. Among these 14 objects, two were not yet subject to a detailed abundance study in the literature. We apply the same method to obtain accurate abundances for the 12 others. Our homogeneous abundance results provide the input of detailed spectral synthesis computations in the spectral regions where Pb lines are located. We used high-resolution UVES and HERMES spectra for detailed spectral abundance studies of our sample of Galactic post-AGB stars. None of the sample stars display clear Pb lines, and we only deduced upper limits of the Pb abundance by using spectrum synthesis in the spectral ranges of the strongest Pb lines.
