- ID:
- ivo://CDS.VizieR/J/ApJ/682/1217
- Title:
- Abundances in red giants in 7 globular clusters
- Short Name:
- J/ApJ/682/1217
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a technique that applies spectral synthesis to medium-resolution spectroscopy (MRS; R~6000) in the red (6300{AA}<{lambda}<9100{AA}) to measure [Fe/H] and [{alpha}/Fe] of individual red giant stars over a wide metallicity range. We apply our technique to 264 red giant stars in seven Galactic globular clusters and demonstrate that it reproduces the metallicities and {alpha}-enhancements derived from high-resolution spectroscopy (HRS). The MRS technique excludes the three CaII triplet lines and instead relies on a plethora of weaker lines. Unlike empirical metallicity estimators, such as the equivalent width of the CaII triplet, the synthetic method presented here is applicable over an arbitrarily wide metallicity range and is independent of assumptions about the {alpha}-enhancement.
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- ID:
- ivo://CDS.VizieR/J/ApJ/824/73
- Title:
- Abundances of NGC 6362 member stars
- Short Name:
- J/ApJ/824/73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first measure of Fe and Na abundances in NGC 6362, a low-mass globular cluster (GC) where first- and second-generation stars are fully spatially mixed. A total of 160 member stars (along the red giant branch (RGB) and the red horizontal branch (RHB)) were observed with the multi-object spectrograph FLAMES at the Very Large Telescope. We find that the cluster has an iron abundance of [Fe/H]=-1.09+/-0.01dex, without evidence of intrinsic dispersion. On the other hand, the [Na/Fe] distribution turns out to be intrinsically broad and bimodal. The Na-poor and Na-rich stars populate, respectively, the bluest and the reddest RGBs detected in the color-magnitude diagrams including the U filter. The RGB is composed of a mixture of first- and second-generation stars in a similar proportion, while almost all the RHB stars belong to the first cluster generation. To date, NGC 6362 is the least massive GC where both the photometric and spectroscopic signatures of multiple populations have been detected.
- ID:
- ivo://CDS.VizieR/J/MNRAS/475/257
- Title:
- AGB subpopulations in NGC 6397
- Short Name:
- J/MNRAS/475/257
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It has been well established that Galactic Globular clusters (GCs) harbour more than one stellar population, distinguishable by the anticorrelations of light-element abundances (C-N, Na-O, and Mg-Al). These studies have been extended recently to the asymptotic giant branch (AGB). Here, we investigate the AGB of NGC 6397 for the first time. We have performed an abundance analysis of high-resolution spectra of 47 red giant branch (RGB) and eight AGB stars, deriving Fe, Na, O, Mg, and Al abundances. We find that NGC 6397 shows no evidence of a deficit in Na-rich AGB stars, as reported for some other GCs - the subpopulation ratios of the AGB and RGB in NGC 6397 are identical, within uncertainties. This agrees with expectations from stellar theory. This GC acts as a control for our earlier work on the AGB of M4 (with contrasting results), since the same tools and methods were used.
- ID:
- ivo://CDS.VizieR/J/ApJ/647/1075
- Title:
- Age-metallicity relation of {omega} Cen
- Short Name:
- J/ApJ/647/1075
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a metallicity distribution based on photometry and spectra for 442 Omega Centauri cluster members that lie at the main-sequence turnoff region of the color-magnitude diagram. This distribution is similar to that found for the red giant branch. The distribution shows a sharp rise to a mean of [Fe/H]=-1.7 with a long tail to higher metallicities. Ages have then been determined for the stars using theoretical isochrones enabling the construction of an age-metallicity diagram. Interpretation of this diagram is complicated by the correlation of the errors in the metallicities and ages. Nevertheless, after extensive Monte Carlo simulations, we conclude that our data show that the formation of the cluster took place over an extended period of time: the most metal-rich stars in our sample ([Fe/H]~-0.6) are younger by 2-4Gyr than the most metal-poor population.
- ID:
- ivo://CDS.VizieR/J/ApJ/725/200
- Title:
- An updated catalog of M31 globular-like clusters
- Short Name:
- J/ApJ/725/200
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an updated UBVRI photometric catalog containing 970 objects in the field of M31, selected from the Revised Bologna Catalog (RBC v.4.0), including 965, 967, 965, 953, and 827 sources in the individual UBVRI bands, respectively, of which 205, 123, 14, 126, and 109 objects do not have previously published photometry. Photometry is performed using archival images from the Local Group Galaxies Survey, which covers 2.2deg^2^ along the major axis of M31. Detailed comparisons show that our photometry is fully consistent with previous measurements in all filters. We focus on 445 confirmed "globular-like" clusters and candidates, comprising typical globular and young massive clusters. The ages and masses of these objects are derived by comparing their observed spectral-energy distributions with simple stellar population synthesis. Approximately half of the clusters are younger than 2Gyr, suggesting that there has been significant recent active star formation in M31, which is consistent with previous results.
- ID:
- ivo://CDS.VizieR/J/MNRAS/366/1230
- Title:
- BI photometry of NGC 1407 and NGC 1400 GCs
- Short Name:
- J/MNRAS/366/1230
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present wide-field Keck telescope imaging of the globular cluster (GC) systems around NGC 1407 and 1400 in the Eridanus galaxy cloud. This is complemented by Hubble Space Telescope (HST) images from the Advanced Camera for Surveys of NGC 1407 and Wide Field and Planetary Camera 2 images of NGC 1400.
- ID:
- ivo://CDS.VizieR/J/AJ/108/1786
- Title:
- Blue stragglers and variable stars in M3
- Short Name:
- J/AJ/108/1786
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper describes Hubble Space Telescope (HST)/Planetary Camera-I images of the core of the dense globular cluster M3 (NGC 5272). Stellar photometry in the F555W (V) and F785LP (I) bands, with a 1 sigma photometric accuracy of about 0.1mag, has been used to construct color-magnitude diagrams of about 4700 stars above the main-sequence turnoff within r<~1' of the cluster center. We have also analyzed archival HST F336W (U) images of M3 obtained by the Wide Field/Planetary Camera-I Instrument Definition Team. The UVI data are used to identify 28 blue straggler (BS) stars within the central 0.29arcmin^2. The specific frequency of BSs in this region of M3, N(BS)/N(V<V(HB)+2)=0.094+/-0.019, is about a factor of 2-3 higher than that found by Bolte et al. [1993, ApJ, 408, L89] in a recent ground-based study of the same region, but comparable to that seen in the sparse outer parts of the same cluster and in HST observations of the core of the higher density cluster 47 Tuc. The BSs in M3 are slightly more centrally concentrated than red giant branch stars while horizontal branch stars are somewhat less concentrated than red giants. The radial distribution of V-selected subgiant and turnoff stars is well fit by a King model with a core radius r(core)=28"+/-2" (90% confidence limits), which corresponds to 1.4pc. Red giant and horizontal branch stars selected in the ultraviolet data (U<18) have a somewhat more compact distribution (r(core)=22.5"). The HST U data consist of 17 exposures acquired over a span of three days. We have used these data to isolate 40 variable stars for which relative astrometry, brightnesses, colors, and light curves are presented. A Kolmogorov-Smirnov test indicates that, typically, the variability for each star is significant at the 95% level. We identify two variable BS candidates (probably of the SX Phe type) out of a sample of ~25 BSs in which variability could have been detected. Most of the variables are RR Lyrae stars on the horizontal branch. All of them have periods P>~8h.
- ID:
- ivo://CDS.VizieR/J/ApJ/677/1069
- Title:
- Blue stragglers in NGC 6388
- Short Name:
- J/ApJ/677/1069
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used multiband high-resolution HST WFPC2 and ACS observations combined with wide-field ground-based observations to study the blue straggler star (BSS) population in the Galactic globular cluster NGC 6388. As in several other clusters we have studied, the BSS distribution is found to be bimodal: highly peaked in the cluster center, rapidly decreasing at intermediate radii, and rising again at larger radii. In other clusters the sparsely populated intermediate-radius region (or "zone of avoidance") corresponds well to that part of the cluster where dynamical friction would have caused the more massive BSSs or their binary progenitors to settle to the cluster center. Instead, in NGC 6388, BSSs still populate a region that should have been cleaned out by dynamical friction effects, thus suggesting that dynamical friction is somehow less efficient than expected. As a by-product of these observations, the peculiar morphology of the horizontal branch (HB) is also confirmed. In particular, within the (very extended) blue portion of the HB we are able to clearly characterize three subpopulations: ordinary blue HB stars, extreme HB stars, and blue hook stars. Each of these populations has a radial distribution which is indistinguishable from normal cluster stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/663/277
- Title:
- BVI of NGC 5466 red giants and blue stragglers
- Short Name:
- J/ApJ/663/277
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present wide-field BVI photometry for about 11500 stars in the low-metallicity cluster NGC 5466. We have detected the red giant branch bump for the first time, although it is at least 0.2mag fainter than expected relative to the turnoff. The number of red giants (relative to main-sequence turnoff stars) is in excellent agreement with stellar models from the Yonsei-Yale and Teramo groups, and slightly high compared to Victoria-Regina models. This adds to evidence that an abnormally large ratio of red giant to main-sequence stars is not correlated with cluster metallicity.
- ID:
- ivo://CDS.VizieR/J/ApJ/871/33
- Title:
- BVI photometric calatog of star clusters in NGC4589
- Short Name:
- J/ApJ/871/33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NGC4589, a bright E2 merger-remnant galaxy, hosts the peculiar fast and faint calcium-rich supernova SNIb SN2005cz. The progenitor of Ca-rich SNeIb has been controversial: it could be (1) a young, massive star with 6-12M{sun} in a binary system, or (2) an old, low-mass star in a binary system that was kicked out from the galaxy center. Moreover, previous distance estimates for this galaxy have shown a large spread, ranging from 20 to 60Mpc. Thus, using archival Hubble Space Telescope/Advanced Camera for Surveys (HST/ACS) F435W, F555W, and F814W images, we search for star clusters in NGC4589 in order to help resolve these issues. We find a small population of young star clusters with 25<V<=27(-7.1<M_V_<-5.1)mag and age <1Gyr in the central region at R<0.5' (<3.8kpc), thus supporting the massive-star progenitor scenario for SN2005cz. In addition to young star clusters, we also find a large population of old globular clusters. In contrast to previous results in the literature, we find that the color distribution of the globular clusters is clearly bimodal. The turnover (Vega) magnitude in the V-band luminosity functions of the blue (metal-poor) globular clusters is determined to be V_0_(max)=24.40{+/-}0.10mag. We derive the total number of globular clusters, N_GC_=640{+/-}50, and the specific frequency, S_N_=1.7{+/-}0.2. Adopting a calibration for the metal-poor globular clusters, M_V_(max) =-7.66{+/-}0.14mag, we derive a distance to this galaxy: (m-M)_0_=32.06{+/-}0.10(ran){+/-}0.15(sys) (d=25.8{+/-}2.2Mpc).