- 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.
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- 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.
- 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.
- 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.
- ID:
- ivo://CDS.VizieR/J/AJ/135/836
- Title:
- Calcium triplet index in LMC stars
- Short Name:
- J/AJ/135/836
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Infrared CaII triplet (CaT) spectroscopy has been used to derive stellar metallicities for individual stars in four Large Magellanic Cloud fields situated at galactocentric distances of 3{deg}, 5{deg}, 6{deg}, and 8{deg} to the north of the bar. The combination of spectroscopy with deep CCD photometry has allowed us to break the RGB age-metallicity degeneracy and compute the ages for the objects observed spectroscopically. The obtained age-metallicity relationships (AMRs) for our four fields are statistically indistinguishable. We conclude that the lower mean metallicity in the outermost field is a consequence of it having a lower fraction of intermediate-age stars, which are more metal-rich than the older stars. The disk AMR is similar to that for clusters. However, the lack of objects with ages between 3 and 10Gyr is not observed in the field population. Finally, we used data from the literature to derive consistently the AMR of the bar. Simple chemical evolution models have been used to reproduce the observed AMRs with the purpose of investigating which mechanism has participated in the evolution of the disk and bar.
- ID:
- ivo://CDS.VizieR/J/MNRAS/421/3622
- Title:
- Candidate Be stars in the Magellanic Clouds
- Short Name:
- J/MNRAS/421/3622
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Mennickent et al. (2002A&A...393..887M) and Sabogal et al. (2005, Cat. J/MNRAS/361/1055) identified a large number of classical Be (CBe) candidates (~3500) in the Large and Small Magellanic Clouds (LMC and SMC) based on their photometric variability using the OGLE II data base (Udalski et al., 1998, Cat. J/AcA/48/147; 2000, Cat. J/AcA/50/307). They classified these stars into four different groups based on the appearance of their variability. In order to refine and understand the nature of this large number of stars, we studied the infrared properties of the sample and the spectroscopic properties of a subsample. We cross-correlated the optical sample with the IRSF-MCPS catalogue to obtain the J, H, Ks magnitudes of all the four types of stars (~2500) in the LMC and SMC. Spectra of 120 stars belonging to the types 1, 2 and 3 were analysed to study their spectral properties.
- ID:
- ivo://CDS.VizieR/J/AJ/149/78
- Title:
- Candidate IR variables from SAGE-SMC survey
- Short Name:
- J/AJ/149/78
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present our study on the infrared variability of point sources in the Small Magellanic Cloud (SMC). We use the data from the Spitzer Space Telescope Legacy Program "Surveying the Agents of Galaxy Evolution in the Tidally Stripped, Low Metallicity Small Magellanic Cloud" (SAGE-SMC) and the "Spitzer Survey of the Small Magellanic Cloud" (S^3^MC) survey, over three different epochs, separated by several months to 3 years. Variability in the thermal infrared is identified using a combination of Spitzer's InfraRed Array Camera 3.6, 4.5, 5.8, and 8.0{mu}m bands, and the Multiband Imaging Photometer for Spitzer 24{mu}m band. An error-weighted flux difference between each pair of three epochs ("variability index") is used to assess the variability of each source. A visual source inspection is used to validate the photometry and image quality. Out of ~2 million sources in the SAGE-SMC catalog, 814 meet our variability criteria. We matched the list of variable star candidates to the catalogs of SMC sources classified with other methods, available in the literature. Carbon-rich Asymptotic Giant Branch (AGB) stars make up the majority (61%) of our variable sources, with about a third of all of our sources being classified as extreme AGB stars. We find a small, but significant population of oxygen-rich (O-rich) AGB (8.6%), Red Supergiant (2.8%), and Red Giant Branch (<1%) stars. Other matches to the literature include Cepheid variable stars (8.6%), early type stars (2.8%), Young-stellar objects (5.8%), and background galaxies (1.2%). We found a candidate OH maser star, SSTISAGE1C J005212.88-730852.8, which is a variable O-rich AGB star, and would be the first OH/IR star in the SMC, if confirmed. We measured the infrared variability of a rare RV Tau variable (a post-AGB star) that has recently left the AGB phase. 59 variable stars from our list remain unclassified.
- ID:
- ivo://CDS.VizieR/J/MNRAS/376/313
- Title:
- Carbon star in Magellanic Cloud
- Short Name:
- J/MNRAS/376/313
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Dust radiative transfer models are presented for 60 carbon stars in the Magellanic Clouds (MCs) for which 535m Spitzer infrared spectrograph (IRS) spectra and quasi-simultaneous ground-based JHKL photometry are available. From the modelling, the luminosity and mass-loss rate are derived (under the assumption of a fixed expansion velocity and dust-to-gas ratio), and the ratio of silicon carbide (SiC) to amorphous carbon (AMC) dust is also derived. This ratio is smaller than observed in Galactic carbon stars, as has been noted before. Light curves for 36 objects can be retrieved from the massive compact halo object (MACHO) and optical gravitational lensing experiment (OGLE) data bases, and periods can be derived for all but two of these. Including data from the literature, periods are available for 53 stars.
- ID:
- ivo://CDS.VizieR/J/A+AS/122/463
- Title:
- Carbon stars in Magellanic Clouds
- Short Name:
- J/A+AS/122/463
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The 16 tables list the heliocentric and galactocentric radial velocities of several hundred carbon stars in the halo of the LMC and SMC. Most of them are newly discovered stars.
- ID:
- ivo://CDS.VizieR/J/ApJS/171/419
- Title:
- Catalog of LMC HI clouds
- Short Name:
- J/ApJS/171/419
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- 21cm neutral hydrogen interferometric survey of the Large Magellanic Cloud (LMC) combined with the Parkes multibeam HI single-dish survey (2003MNRAS.339...87S) clearly shows that the HI gas is distributed in the form of clumps or clouds. The HI clouds and clumps have been identified using a thresholding method with three separate brightness temperature thresholds (T_b_). Each catalog of HI cloud candidates shows a power-law relationship between the sizes and the velocity dispersions of the clouds roughly following the Larson law scaling {sigma}_v_{prop.to}R^0.5^, with steeper indices associated with dynamically hot regions. The clouds in each catalog have roughly constant virial parameters as a function of mass, suggesting that the clouds are all in roughly the same dynamical state, but the values of the virial parameter are significantly larger than unity, showing that turbulent motions dominate gravity in these clouds. The mass distribution of the clouds is a power law with differential indices between -1.6 and -2.0 for the three catalogs. In contrast, the distribution of mean surface densities is a lognormal distribution.
