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Start Over Subject globular star clusters Subject infrared photometry Subject optical astronomy
1. Abundances and velocities of NGC 6397 stars
ID:
ivo://CDS.VizieR/J/ApJ/754/91
Title:
Abundances and velocities of NGC 6397 stars
Short Name:
J/ApJ/754/91
Date:
21 Oct 2021
Publisher:
CDS
Description:
We used three sets of high-resolution spectra acquired with the multifiber facility FLAMES at the Very Large Telescope of the European Southern Observatory to investigate the chemical and kinematical properties of a sample of 42 horizontal branch (HB) stars, 18 blue straggler stars (BSSs), and 86 main-sequence (MS) turnoff (TO) and sub-giant branch stars in the nearby globular cluster NGC 6397. We measured rotational velocities and Fe, O, and Mg abundances. All of the unevolved stars in our sample have low rotational velocites (vsin i<10km/s), while the HB stars and BSSs show a broad distribution, with values ranging from 0 to ~70km/s. For HB stars with T<10500K there is a clear temperature-oxygen anticorrelation that can be understood if the star position along the HB is mainly determined by the He content. The hottest BSSs and HB stars (with temperatures T>8200K and T>10500K, respectively) also show significant deviations in their iron abundance with respect to the cluster metallicity (as traced by the unevolved stars, [Fe/H]=-2.12). While similar chemical patterns have already been observed in other hot HB stars, this is the first evidence ever collected for BSSs. We interpret these abundance anomalies as due to the metal radiative levitation, occurring in stars with shallow or no convective envelopes.
2. Abundances in red giants in 7 globular clusters
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.
3. AGB subpopulations in NGC 6397
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.
4. An updated catalog of M31 globular-like clusters
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.
5. BI photometry of NGC 1407 and NGC 1400 GCs
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.
6. BVIc light curves of 3 type II Cepheids
ID:
ivo://CDS.VizieR/J/AJ/139/2300
Title:
BVIc light curves of 3 type II Cepheids
Short Name:
J/AJ/139/2300
Date:
21 Oct 2021
Publisher:
CDS
Description:
Light curves in the B, V, and Ic passbands have been obtained for the type II Cepheids V154 in M3 and V42 and V84 in M5. Alternating cycle behavior, similar to that seen among RV Tauri variables, is confirmed for V84. Old and new observations, spanning more than a century, show that V154 has increased in period while V42 has decreased in period. V84, on the other hand, has shown large, erratic changes in period that do not appear to reflect the long-term evolution of V84 through the Hertzsprung-Russel diagram.
7. BVI of NGC 5466 red giants and blue stragglers
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.
8. BVI photometric calatog of star clusters in NGC4589
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).
9. BVI photometry in M55 (NGC 6809)
ID:
ivo://CDS.VizieR/J/AJ/134/825
Title:
BVI photometry in M55 (NGC 6809)
Short Name:
J/AJ/134/825
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have compiled the asymptotic giant, horizontal, and upper red giant branch (AGB, HB, and RGB) stars in the globular cluster M55 (NGC 6809). Using the star counts and the R-parameter we compute the initial helium abundance Y=0.274+/-0.016.
10. BVI photometry of M15 stars
ID:
ivo://CDS.VizieR/J/PASP/126/733
Title:
BVI photometry of M15 stars
Short Name:
J/PASP/126/733
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present new BVI photometry containing 40,000 stars of the Galactic globular cluster M15 (NGC 7078), covering a 25'x25' area centered on the cluster with a magnitude range from the tip of the red giant branch to 3 mag below the main sequence turnoff. Using {alpha}-enhanced Dartmouth Stellar Evolution Program models, we find an age of 13.0+/-1.0Gyr and distance modulus of (m-M)_V_=15.4+/-0.1 through isochrone fitting. Unlike previous works, we find good agreement between the observed completeness-corrected stellar luminosity function and models.

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