- ID:
- ivo://CDS.VizieR/J/ApJ/637/1102
- Title:
- Lick indices for metal-rich stars
- Short Name:
- J/ApJ/637/1102
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present empirical calibrations that provide estimates of stellar metallicity, effective temperature, and surface gravity as a function of Lick IDS indices. These calibrations have been derived from a training set of 261 stars for which (1) high-precision measurements of [Fe/H], Teff, and log(g) have been made using spectral-synthesis analysis of HIRES spectra, and (2) Lick indices have also been measured.
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- 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.
- 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/A+A/489/403
- Title:
- Line abundances for solar stars
- Short Name:
- J/A+A/489/403
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the abundance measurements of several elements (Fe, Ca, Na, Ni, Ti, Al, Cr, Si) for 20 solar-type stars belonging to four Galactic open clusters: NGC 3680, IC 4651, Praesepe, and M 67. Oxygen abundances were in addition measured for most stars in each cluster apart from IC 4651. For NGC 3680, accurate abundance determinations using high-resolution spectra covering a large spectral domain are computed for the first time. We used UVES high-resolution, high signal-to-noise (S/N) ratio spectra and performed a differential analysis with respect to the sun, by measuring equivalent widths and assuming LTE.
- ID:
- ivo://CDS.VizieR/J/A+A/633/L9
- Title:
- Linear regression fit coefficients
- Short Name:
- J/A+A/633/L9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The physical processes driving chemical evolution in the Milky Way can be probed using the distribution of abundances in low-mass FGK type stars in space phase at different times. During their final stages of evolution, stars experience nucleosynthesis several times, each at different timescales and producing different chemical elements. Finding abundance ratios that have simple variations across cosmic times therefore remains a challenge. Using the sample of 80 solar twins for which ages and abundances of 30 elements have been measured with high precision, we searched for all possible abundance ratio combinations that show linear trends with age. We found 55 such ratios, all combining an n-capture element and another element produced by different nucleosynthesis channels. We recovered the ratios of [Y/Mg], [Ba/Mg], and [Al/Y] that have been reported previously in the literature, and found that [C/Ba] depends most strongly on age, with a slope of 0.049+/-0.003dex/Gyr. This imposes constraints on the magnitude of the time dependency of abundance ratios in solar twins. Our results suggest that s-process elements, in lieu of Fe, should be used as a reference for constraining chemical evolution models of the solar neighbourhood. Our study illustrates that a wide variety of chemical elements measured in high-resolution spectra is key to meeting the current challenges in understanding the formation and evolution of our Galaxy.
- 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/A+A/588/A81
- Title:
- Line list and abundances of the binary zet2 Ret
- Short Name:
- J/A+A/588/A81
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We explore condensation temperature Tc trends in the binary system zet1 Ret - zet2 Ret, to determine whether there is a depletion of refractories, which could be related to the planet formation process. The star zet2 Ret hosts a debris disk which was detected by an IR excess and confirmed by direct imaging and numerical simulations, while zet1 Ret does not present IR excess nor planets. We derived differential abundances of 24 different species with equivalent widths and spectral synthesis. The star zet1 Ret resulted slightly more metal rich than zet2 Ret by 0.02dex, and the relative abundances showed a positive Tc trend. Then, we propose an scenario in which the refractory elements depleted in zet2 Ret are possibly locked-up in the rocky material that orbits this star and produce the debris disk observed around this object.