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1901. CaII index of SMC red giant branch stars
ID:
ivo://CDS.VizieR/J/AJ/136/1039
Title:
CaII index of SMC red giant branch stars
Short Name:
J/AJ/136/1039
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present stellar metallicities derived from Ca II triplet spectroscopy in over 350 red giant branch stars in 13 fields distributed in different positions in the Small Magellanic Cloud, ranging from ~1{deg} to ~4{deg} from its center. In the innermost fields, the average metallicity is [Fe/H]~-1. This value decreases when we move away toward outermost regions. This is the first detection of a spectroscopic metallicity gradient in this galaxy. We show that the metallicity gradient is related to an age gradient, in the sense that more metal-rich stars, which are also younger, are concentrated in the central regions of the galaxy.
1902. CaII in extragalactic red giants
ID:
ivo://CDS.VizieR/J/MNRAS/327/918
Title:
CaII in extragalactic red giants
Short Name:
J/MNRAS/327/918
Date:
21 Oct 2021
Publisher:
CDS
Description:
Spectroscopic abundance determinations for stars spanning a Hubble time in age are necessary in order to determine unambiguously the evolutionary histories of galaxies. Using FORS1 in multi-object spectroscopy mode on ANTU (UT1) at the ESO VLT on Paranal, we have obtained near-infrared spectra from which we have measured the equivalent widths of the two strongest Ca II triplet lines to determine metal abundances for a sample of red giant branch stars, selected from ESO NTT optical (I, V-I) photometry of three nearby Local Group galaxies: the Sculptor dwarf spheroidal, the Fornax dwarf spheroidal and the dwarf irregular NGC 6822. The summed equivalent width of the two strongest lines in the Ca II triplet absorption-line feature, centred at 8500{AA}, can be readily converted into an [Fe/H] abundance using the previously established calibrations by Armandroff & Da Costa (1991AJ....101.1329A) and Rutledge, Hesser & Stetson (1997, Cat. <J/PASP/109/883>). We have measured metallicities for 37 stars in Sculptor, 32 stars in Fornax and 23 stars in NGC 6822, yielding more precise estimates of the metallicity distribution functions for these galaxies than it is possible to obtain photometrically. In the case of NGC 6822, this is the first direct measurement of the abundances of the intermediate-age and old stellar populations. We find metallicity spreads in each galaxy which are broadly consistent with the photometric width of the red giant branch, although the abundances of individual stars do not always appear to correspond to their colour. This is almost certainly predominantly due to a highly variable star formation rate with time in these galaxies, which results in a non-uniform, non-globular-cluster-like evolution of the Ca/Fe ratio.
1903. CaIIK spectra of 7 Galactic and MC open clusters
ID:
ivo://CDS.VizieR/J/A+A/582/A59
Title:
CaIIK spectra of 7 Galactic and MC open clusters
Short Name:
J/A+A/582/A59
Date:
21 Oct 2021
Publisher:
CDS
Description:
The large and small-scale (pc) structure of the Galactic interstellar medium can be investigated by utilising spectra of early- type stellar probes of known distances in the same region of the sky. This paper determines the variation in line strength of CaII at 3933.661{AA} as a function of probe separation for a large sample of stars, including a number of sightlines in the Magellanic Clouds. FLAMES-GIRAFFE data taken with the Very Large Telescope towards early-type stars in 3 Galactic and 4 Magellanic open clusters in CaII are used to obtain the velocity, equivalent width, column density, and line width of interstellar Galactic calcium for a total of 657 stars, of which 443 are Magellanic Cloud sightlines. In each cluster there are between 43 and 111 stars observed. Additionally, FEROS and UVES CaII K and NaI D spectra of 21 Galactic and 154 Magellanic early-type stars are presented and combined with data from the literature to study the calcium column density - parallax relationship.
1904. CaII spectroscopy in Magellanic Cloud clusters
ID:
ivo://CDS.VizieR/J/AJ/132/1630
Title:
CaII spectroscopy in Magellanic Cloud clusters
Short Name:
J/AJ/132/1630
Date:
21 Oct 2021
Publisher:
CDS
Description:
Using the FORS2 instrument on the Very Large Telescope, we have obtained near-infrared spectra for more than 200 stars in 28 populous LMC clusters. This cluster sample spans a large range of ages (~113Gyr) and metallicities (-0.3>~[Fe/H]>~-2.0) and has good areal coverage of the LMC disk. The strong absorption lines of the Ca II triplet are used to derive cluster radial velocities and abundances. We determine mean cluster velocities to typically 1.6km/s and mean metallicities to 0.04dex (random error). For eight of these clusters, we report the first spectroscopically determined metallicities based on individual cluster stars, and six of these eight have no published radial velocity measurements. Combining our data with archival Hubble Space Telescope WFPC2 photometry, we find that the newly measured cluster, NGC 1718, is one of the most metal-poor ([Fe/H]~-0.80) intermediate-age (~2Gyr) inner disk clusters in the LMC. Similar to what was found by previous authors, this cluster sample has radial velocities consistent with that of a single rotating disk system, with no indication that the newly reported clusters exhibit halo kinematics. In addition, our findings confirm previous results that show that the LMC lacks the metallicity gradient typically seen in non-barred spiral galaxies, suggesting that the bar is driving the mixing of stellar populations in the LMC.
1905. CaII spectroscopy of SMC fields stars
ID:
ivo://CDS.VizieR/J/AJ/139/1168
Title:
CaII spectroscopy of SMC fields stars
Short Name:
J/AJ/139/1168
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have obtained metallicities of ~360 red giant stars distributed in 15 Small Magellanic Cloud (SMC) fields from near-infrared spectra covering the CaII triplet lines using the VLT + FORS2.
1906. CaII spectroscopy of SMC red giants
ID:
ivo://CDS.VizieR/J/AJ/138/517
Title:
CaII spectroscopy of SMC red giants
Short Name:
J/AJ/138/517
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have obtained near-infrared spectra covering the CaII triplet lines for a large number of stars associated with 16 Small Magellanic Cloud (SMC) clusters using the VLT + FORS2. These data compose the largest available sample of SMC clusters with spectroscopically derived abundances and velocities. Our clusters span a wide range of ages and provide good areal coverage of the galaxy.
1907. CaII spectroscopy of SMC red giants. III.
ID:
ivo://CDS.VizieR/J/AJ/149/154
Title:
CaII spectroscopy of SMC red giants. III.
Short Name:
J/AJ/149/154
Date:
21 Oct 2021
Publisher:
CDS
Description:
We obtained spectra of red giants in 15 Small Magellanic Cloud (SMC) clusters in the region of the CaII lines with FORS2 on the Very Large Telescope. We determined the mean metallicity and radial velocity with mean errors of 0.05dex and 2.6km/s, respectively, from a mean of 6.5 members per cluster. One cluster (B113) was too young for a reliable metallicity determination and was excluded from the sample. We combined the sample studied here with 15 clusters previously studied by us using the same technique, and with 7 clusters whose metallicities determined by other authors are on a scale similar to ours. This compilation of 36 clusters is the largest SMC cluster sample currently available with accurate and homogeneously determined metallicities. We found a high probability that the metallicity distribution is bimodal, with potential peaks at -1.1 and -0.8dex. Our data show no strong evidence of a metallicity gradient in the SMC clusters, somewhat at odds with recent evidence from CaII triplet spectra of a large sample of field stars. This may be revealing possible differences in the chemical history of clusters and field stars. Our clusters show a significant dispersion of metallicities, whatever age is considered, which could be reflecting the lack of a unique age-metallicity relation in this galaxy. None of the chemical evolution models currently available in the literature satisfactorily represents the global chemical enrichment processes of SMC clusters.
1908. CaII spectroscopy of SMC red giants. IV.
ID:
ivo://CDS.VizieR/J/AJ/152/58
Title:
CaII spectroscopy of SMC red giants. IV.
Short Name:
J/AJ/152/58
Date:
21 Oct 2021
Publisher:
CDS
Description:
This paper represents a major step forward in the systematic and homogeneous study of Small Magellanic Cloud (SMC) star clusters and field stars carried out by applying the calcium triplet technique. We present in this work the radial velocity and metallicity of approximately 400 red giant stars in 15 SMC fields, with typical errors of about 7km/s and 0.16dex, respectively. We added to this information our previously determined metallicity values for 29 clusters and approximately 350 field stars using the identical techniques. Using this enlarged sample, we analyze the metallicity distribution and gradient in this galaxy. We also compare the chemical properties of the clusters and of their surrounding fields. We find a number of surprising results. While the clusters, taken as a whole, show no strong evidence for a metallicity gradient (MG), the field stars exhibit a clear negative gradient in the inner region of the SMC, consistent with the recent results of Dobbie et al. For distances to the center of the galaxy less than 4{deg}, field stars show a considerably smaller metallicity dispersion than that of the clusters. However, in the external SMC regions, clusters and field stars exhibit similar metallicity dispersions. Moreover, in the inner region of the SMC, clusters appear to be concentrated in two groups: one more metal-poor and another more metal-rich than field stars. Individually considered, neither cluster group presents an MG. Most surprisingly, the MG for both stellar populations (clusters and field stars) appears to reverse sign in the outer regions of the SMC. The difference between the cluster metallicity and the mean metallicity of the surrounding field stars turns out to be a strong function of the cluster metallicity. These results could be indicating different chemical evolution histories for these two SMC stellar populations. They could also indicate variations in the chemical behavior of the SMC in its internal and external regions.
1909. CaII triplet equivalent widths in 30 globulars
ID:
ivo://CDS.VizieR/J/A+A/563/A76
Title:
CaII triplet equivalent widths in 30 globulars
Short Name:
J/A+A/563/A76
Date:
21 Oct 2021
Publisher:
CDS
Description:
When they are established with sufficient precision, the ages, metallicities and kinematics of Galactic globular clusters (GGCs) can shed much light on the dynamical and chemical evolution of the Galactic halo and bulge. While the most fundamental way of determining GC abundances is by mean high-resolution spectroscopy, in practice this method is limited to only the brighter stars in the nearest and less reddened objects. This restriction has, over the years, led to the development of a large number of techniques that measure the overall abundance indirectly from parameters that correlate with overall metallicity. One of the most efficient methods is measuring of the equivalent width (EW) of the calcium II triplet (CaT) at {lambda}~~8500{AA} in red giants, which are corrected for the luminosity and temperature effects using the V magnitude differences from the horizontal branch (HB). We establish a similar method in the near-infrared (NIR), by combining the power of the differential magnitudes technique with the advantages of NIR photometry to minimize differential reddening effects. We used the Ks magnitude difference between the star and the reddest part of the HB (RHB) or of the red clump (RC) to generate reduced equivalent widths (rEW) from the previously presented datasets. Then we calibrated these rEW against three previously reported different metallicity scales; one of which we corrected using high-resolution spectroscopic metallicities.
1910. CaII triplet in red giant spectra
ID:
ivo://CDS.VizieR/J/MNRAS/455/199
Title:
CaII triplet in red giant spectra
Short Name:
J/MNRAS/455/199
Date:
21 Oct 2021
Publisher:
CDS
Description:
Measurements are presented and analysed of the strength of the CaII triplet lines in red giants in Galactic globular and open clusters, and in a sample of red giants in the LMC disc that have significantly different [Ca/Fe] abundance ratios to the Galactic objects. The Galactic objects are used to generate a calibration between CaII triplet line strength and [Fe/H], which is then used to estimate [Fe/H]CaT for the LMC stars. The values are then compared with the [Fe/H]spec determinations from high-dispersion spectroscopy. After allowance for a small systematic offset, the two abundance determinations are in excellent agreement. Further, as found in earlier studies, the difference is only a very weak function of the [Ca/Fe] ratio. For example, changing [Ca/Fe] from +0.3 to -0.2 causes the CaII-based abundance to underestimate [Fe/H]spec by only ~0.15dex, assuming a Galactic calibration. Consequently, the CaII triplet approach to metallicity determinations can be used without significant bias to study stellar systems that have substantially different chemical evolution histories.

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