- ID:
- ivo://CDS.VizieR/J/AJ/134/2168
- Title:
- BVI photometry of M33 star clusters
- Short Name:
- J/AJ/134/2168
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a survey for star clusters in M33 using HST WFPC2 archive images. We have found 104 star clusters, including 32 new ones, in the images of 24 fields that were not included in previous studies. Combining these with previous data in the literature, we increase the number of M33 star clusters found in the HST images to 242. We have derived BVI integrated photometry of these star clusters from the CCD images taken with the CFH12k mosaic camera at the CFHT.
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- ID:
- ivo://CDS.VizieR/J/AJ/148/30
- Title:
- BVI photometry of 350 Pleiades stars
- Short Name:
- J/AJ/148/30
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new BVI_C_ photometry for 350 Pleiades proper motion members with 9<V<~17. Importantly, our new catalog includes a large number of K- and early M-type stars, roughly doubling the number of low-mass stars with well-calibrated Johnson/Cousins photometry in this benchmark cluster. We combine our new photometry with existing photometry from the literature to define a purely empirical isochrone at Pleiades age ({approx}100Myr) extending from V=9 to 17. We use the empirical isochrone to identify 48 new probable binaries and 14 likely nonmembers. The photometrically identified single stars are compared against their expected positions in the color-magnitude diagram (CMD). At 100Myr, the mid K and early M stars are predicted to lie above the zero-age main sequence (ZAMS) having not yet reached the ZAMS. We find in the B-V versus V CMD that mid K and early M dwarfs are instead displaced below (or blueward of) the ZAMS. Using the stars' previously reported rotation periods, we find a highly statistically significant correlation between rotation period and CMD displacement, in the sense that the more rapidly rotating stars have the largest displacements in the B-V CMD.
- ID:
- ivo://CDS.VizieR/J/A+A/561/A106
- Title:
- BV photometry of 6 SMC stellar clusters
- Short Name:
- J/A+A/561/A106
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Stellar clusters in the Small Magellanic Cloud (SMC) are useful probes to study the chemical and dynamical evolution of this neighbouring dwarf galaxy, enabling inspection of a large period covering over 10Gyr. The main goals of this work are the derivation of age, metallicity, distance modulus, reddening, core radius and central density profile for six sample clusters, in order to place them in the context of the Small Cloud evolution. The studied clusters are: AM 3, HW 1, HW 34, HW 40, Lindsay 2, and Lindsay 3, where HW 1, HW 34, and Lindsay 2 are studied for the first time. Optical Colour-Magnitude Diagrams (V, B-V CMDs) and radial density profiles were built from images obtained with the 4.1m SOAR telescope, reaching V~23. The determination of structural parameters were carried out applying King profile fitting. The other parameters were derived in a self-consistent way by means of isochrone fitting, which uses the likelihood statistics to identify the synthetic CMDs that best reproduce the observed ones. Membership probabilities were determined comparing the cluster and control field CMDs. Completeness and photometric uncertainties were obtained performing artificial star tests. The results confirm that these clusters (except HW 34, identified as a field fluctuation) are intermediate-age clusters, with ages between 1.2Gyr (Lindsay 3) and ~5.0Gyr (HW 1). In particular HW 1, Lindsay 2, and Lindsay 3 are located in a region that we called West Halo, where studies on ages and metallicity gradients are still lacking. Moreover Lindsay 2 was identified as a moderately metal-poor cluster with [Fe/H]=-1.4+/-0.2dex, lower than expected from the age-metallicity relation by Pagel & Tautvaisiene (1998MNRAS.299..535P). We also found distances varying from ~53 to 66kpc, compatible with the large depth of the SMC.
- ID:
- ivo://CDS.VizieR/J/PASP/97/753
- Title:
- BVR CCD photometry on NGC 1777
- Short Name:
- J/PASP/97/753
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present photographic (B and V) and CCD (B, V, and R) photometry of stars in the remote LMC cluster NGC 1777, and integrated UBV photometry of the inner part of the cluster. A comparison of the results from the two techniques reveals large (~0.20m) systematic differences which we attribute to the difficulty of faint photometry. The photographic calibration depended on images produced by a Racine wedge, while the CCD calibration was accomplished in a manner analogous to photoelectric photometry. The stellar photometry provides a C-M diagram to V=21.5 which includes an evolved main sequence and a well-populated giant branch. A variety of methods, including comparisons of the observations to two sets of isochrones, allows us to estimate the cluster age as 0.9+/-0.2x10^9^ years. However we are only able to estimate the metallicity ([Fe/H]) crudely as -0.7+/-0.5. The C-M diagrams of the field in three regions near NGC 1777 indicate the presence of stars in the age range 1x10^9^ to >=3x10^9^ years, although we are unable to discern whether a mixture of two or more distinct populations or a continuous distribution of field-star ages is responsible for this spread.
- ID:
- ivo://CDS.VizieR/J/MNRAS/386/1380
- Title:
- BVRI photometry of LMC star clusters
- Short Name:
- J/MNRAS/386/1380
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a CCD photometric and mass function study of nine young Large Magellanic Cloud star clusters, namely NGC 1767, 1994, 2002, 2003, 2006, SL 538, NGC 2011, 2098 and 2136. BVRI data, reaching down to V~21mag, were collected from the 3.5-m NTT/EFOSC2 in subarcsec seeing conditions. For NGC 1767, 1994, 2002, 2003, 2011 and 2136, broad-band photometric CCD data are presented for the first time.
- 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.
- 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.
- 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.
- 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.
