- ID:
- ivo://CDS.VizieR/J/ApJ/801/67
- Title:
- Grid of binary colors in M30 (NGC7099)
- Short Name:
- J/ApJ/801/67
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Two separated sequences of blue straggler stars (BSSs) have been revealed by Ferraro et al. (2009Natur.462.1028F) in the color-magnitude diagram (CMD) of the Milky Way globular cluster M30. Their presence has been suggested to be related to the two BSS formation channels (namely, collisions and mass transfer in close binaries) operating within the same stellar system. The blue sequence was indeed found to be well reproduced by collisional BSS models. In contrast, no specific models for mass-transfer BSSs were available for an old stellar system like M30. Here we present binary evolution models, including case-B mass transfer and binary merging, specifically calculated for this cluster. We discuss in detail the evolutionary track of a 0.9+0.5M_{sun}_ binary, which spends approximately 4Gyr in the BSS region of the CMD of a 13Gyr old cluster. We also run Monte Carlo simulations to study the distribution of mass-transfer BSSs in the CMD and to compare it with the observational data. Our results show that (1) the color and magnitude distribution of synthetic mass-transfer BSSs defines a strip in the CMD that nicely matches the observed red-BSS sequence, thus providing strong support to the mass-transfer origin for these stars; (2) the CMD distribution of synthetic BSSs never attains the observed location of the blue-BSS sequence, thus reinforcing the hypothesis that the latter formed through a different channel (likely collisions); (3) most (~60%) of the synthetic BSSs are produced by mass-transfer models, while the remaining <40% requires the contribution from merger models.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/431/1405
- Title:
- griz and CT1 photometry in M87
- Short Name:
- J/MNRAS/431/1405
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Gemini griz' photometry for 521 globular cluster (GC) candidates in a 5.5x5.5arcmin^2^ field centred 3.8-arcmin to the south and 0.9-arcmin to the west of the centre of the giant elliptical galaxy NGC 4486. All these objects have previously published (C-T1) photometry. We also present new (C-T1) photometry for 338 globulars, within 1.7-arcmin in galactocentric radius, which have (g-z) colours in the photometric system adopted by the Virgo Cluster Survey of the Advanced Camera for Surveys of the Hubble Space Telescope (HST). These photometric data are used to define a self-consistent multicolour grid (avoiding polynomial fits) and preliminarily calibrated in terms of two chemical abundance scales. The resulting multicolour colour-chemical abundance relations are used to test GC chemical abundance distributions. This is accomplished by modelling the 10 GC colour histograms that can be defined in terms of the Cgriz' bands. Our results suggest that the best fit to the GC observed colour histograms is consistent with a genuinely bimodal chemical abundance distribution N_GC_(Z). On the other side, each ('blue' and 'red') GC subpopulation follows a distinct colour-colour relation.
- ID:
- ivo://CDS.VizieR/J/MNRAS/471/1446
- Title:
- Ground-based proper motion of 12 nearby GC
- Short Name:
- J/MNRAS/471/1446
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We derive relative proper motions of stars in the fields of the globular clusters M12, NGC 6362, M4, M55, M22, NGC 6752, NGC 3201, M30, M10, NGC 362, M5 and 47 Tucanae based on data collected between 1997 and 2015 with the 1-m Swope telescope of Las Campanas Observatory. We determine membership class and membership probability for over 446000 objects, and show that these are efficient methods for separating field stars from members of the cluster. In particular, membership probabilities of variable stars and blue/yellow/red stragglers are determined. Finally, we find absolute proper motions for six globular clusters from our sample: M55, NGC 3201, M10, NGC 362, M5 and 47 Tuc. An electronic catalogue of the derived proper motions is publicly available via the internet.
- ID:
- ivo://CDS.VizieR/J/ApJ/336/780
- Title:
- gr photometry of NGC 5053 blue stragglers
- Short Name:
- J/ApJ/336/780
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Twenty-four blue straggler stars have been identified in the low central concentration globular cluster NGC 5053. New deep color-magnitude (C-M) diagrams to 23mag, constructed from photometry of over 6000 stars on 4-shooter CCD frames, show that they form a well-defined sequence in the C-M diagram, extending up to ~2.2mag brighter than the main-sequence turnoff point. The 12 most luminous blue stragglers are found to be significantly more centrally concentrated than the cluster subgiants with magnitudes in the same interval (a similar result is known for the blue stragglers in the globular cluster NGC 5466). Furthermore, they are also found to be more centrally concentrated than the 12 lower luminosity blue stragglers. Comparisons of the projected radial distributions of the bright and faint blue stragglers, with the radial distributions that are expected for stars of mass 0.8, 1.6, and 2.4M_{sun}_, (calculated using multimass King models) suggests that the brightest blue stragglers have an average mass of <M>=1.3+/0.3M_{sun}_, which is less than or comparable to twice the mean mass of a main-sequence turnoff star, and the lower luminosity blue stragglers have a mean mass similar to that of the main-sequence turnoff stars (i.e., M~0.8M_{sun}_). By fitting theoretical isochrones computed by Bell and VandenBerg to the observed main-sequence turnoff and subgiant branch regions of NGC 5053, a distance modulus of (m-M)_0_=16.05+/-0.14mag, and an age of 18+/-3Gyr are derived for NGC 5053. The main-sequence luminosity function shows no sign of "turning over" for stars brighter than M_g_~5mag. For a description of the uvgr photometric system, see e.g. <GCPD/38>
- ID:
- ivo://CDS.VizieR/J/ApJ/803/63
- Title:
- gr photometry of stars in Kim 2
- Short Name:
- J/ApJ/803/63
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of a new, low-luminosity star cluster in the outer halo of the Milky Way. High-quality gr photometry is presented, from which a color-magnitude diagram is constructed, and estimates of age, [Fe/H], [{alpha}/Fe], and distance are derived. The star cluster, which we designate as Kim 2, lies at a heliocentric distance of ~105kpc. With a half-light radius of ~12.8pc and ellipticity of {epsilon}~0.12, it shares the properties of outer halo globular clusters, except for at higher metallicity ([Fe/H]~-1.0) and lower luminosity (M_v_~-1.5). These parameters are similar to those for the globular cluster AM 4, which is considered to be associated with the Sagittarius dwarf spheroidal galaxy. We find evidence of dynamical mass segregation and the presence of extra-tidal stars that suggests that Kim 2 is most likely a star cluster. Spectroscopic observations for radial-velocity membership and chemical abundance measurements are needed to further understand the nature of the object.
- ID:
- ivo://CDS.VizieR/J/A+A/534/A136
- Title:
- Halo red giants from the SEGUE survey
- Short Name:
- J/A+A/534/A136
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a spectroscopic search for halo field stars that originally formed in globular clusters. Using moderate-resolution SDSS-III/SEGUE-2 spectra of 561 red giants with typical halo metallicities (-1.8<=[Fe/H]<=-1.0), we identify 16 stars, 3% of the sample, with CN and CH bandstrength behavior indicating depleted carbon and enhanced nitrogen abundances relative to the rest of the data set. Since globular clusters are the only environment known in which stars form with this pattern of atypical light-element abundances, we claim that these stars are second-generation globular cluster stars that have been lost to the halo field via normal cluster mass-loss processes.
- ID:
- ivo://CDS.VizieR/J/ApJ/829/116
- Title:
- H-band spectroscopic analysis of 25 bright M31 GCs
- Short Name:
- J/ApJ/829/116
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Chemical abundances are presented for 25 M31 globular clusters (GCs), based on moderately high resolution (R=22500) H-band integrated light (IL) spectra from the Apache Point Observatory Galactic Evolution Experiment (APOGEE). Infrared (IR) spectra offer lines from new elements, lines of different strengths, and lines at higher excitation potentials compared to the optical. Integrated abundances of C, N, and O are derived from CO, CN, and OH molecular features, while Fe, Na, Mg, Al, Si, K, Ca, and Ti abundances are derived from atomic features. These abundances are compared to previous results from the optical, demonstrating the validity and value of IR IL analyses. The CNO abundances are consistent with typical tip of the red giant branch stellar abundances but are systematically offset from optical Lick index abundances. With a few exceptions, the other abundances agree between the optical and the IR within the 1{sigma} uncertainties. The first integrated K abundances are also presented and demonstrate that K tracks the {alpha} elements. The combination of IR and optical abundances allows better determinations of GC properties and enables probes of the multiple populations in extragalactic GCs. In particular, the integrated effects of the Na/O anticorrelation can be directly examined for the first time.
- ID:
- ivo://CDS.VizieR/J/AJ/134/321
- Title:
- H{delta} line in globular clusters
- Short Name:
- J/AJ/134/321
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a cautionary study exploring the reliability of the H{delta} line in the integrated spectra of galaxies for determining galaxy ages. Our database consists of the observed integrated spectra of ~120 early-type galaxies, 7 metal-rich globular clusters in M31 and the Galactic globular cluster 47 Tuc, and the open cluster M67. We have measured H{delta} using index definitions designed to assess contamination from the CN molecule in and around H{delta} by choosing combinations of bandpasses that both avoid and include a region of CN molecular lines redward of H{delta}. We find systematic differences in the ages derived from H{delta} measurements among the various definitions when extracting ages from H{delta} in old stellar populations with enhanced CN bands due to nonsolar abundance ratios. We propose that neighboring CN lines have a strong effect on pseudocontinuum and central bandpass levels. For stellar populations that have nonsolar abundance ratios in C and/or N, population synthesis models that do not account for abundance ratio variations cannot accurately reproduce the CN 4216{AA} band, which leads to a corresponding inaccuracy in reproducing the various H{delta} indices. Hence, caution must be used when extracting galaxy ages from the H{delta} line in old stellar populations with significant nonsolar abundance ratios.
- ID:
- ivo://CDS.VizieR/J/ApJ/786/14
- Title:
- He abundances in M30 and NGC 6397
- Short Name:
- J/ApJ/786/14
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the helium abundance of the two metal-poor clusters M30 and NGC 6397. Helium estimates have been obtained by using the high-resolution spectrograph FLAMES at the European Southern Observatory Very Large Telescope and by measuring the He I line at 4471 {AA} in 24 and 35 horizontal branch (HB) stars in M30 and NGC 6397, respectively. This sample represents the largest data set of He abundances collected so far in metal-poor clusters. The He mass fraction turns out to be Y=0.252+/-0.003 ({sigma}=0.021) for M30 and Y=0.241+/-0.004 ({sigma}=0.023) for NGC 6397. These values are fully compatible with the cosmological abundance, thus suggesting that the HB stars are not strongly enriched in He. The small spread of the Y distributions are compatible with those expected from the observed main sequence splitting. Finally, we find a hint of a weak anticorrelation between Y and [O/Fe] in NGC 6397 in agreement with the prediction that O-poor stars are formed by (He-enriched) gas polluted by the products of hot proton-capture reactions.
- ID:
- ivo://CDS.VizieR/J/ApJ/689/1031
- Title:
- Heavy element abundances in giant stars
- Short Name:
- J/ApJ/689/1031
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a comprehensive abundance analysis of 27 heavy elements in bright giant stars of the globular clusters M4 and M5 based on high-resolution, high signal-to-noise ratio spectra obtained with the Magellan Clay Telescope. We confirm and expand on previous results for these clusters by showing that (1) all elements heavier than, and including, Si have constant abundances within each cluster, (2) the elements from Ca to Ni have indistinguishable compositions in M4 and M5, (3) Si, Cu, Zn, and all s-process elements are approximately 0.3dex overabundant in M4 relative to M5, and (4) the r-process elements Sm, Eu, Gd, and Th are slightly overabundant in M5 relative to M4. The cluster-to-cluster abundance differences for Cu and Zn are intriguing, especially in light of their uncertain nucleosynthetic origins. We confirm that stars other than Type Ia supernovae must produce significant amounts of Cu and Zn at or below the clusters' metallicities. If intermediate-mass AGB stars or massive stars are responsible for the Cu and Zn enhancements in M4, the similar [Rb/Zr] ratios and (preliminary) Mg isotope ratios in both clusters may be problematic for either scenario. For the elements from Ba to Hf, we assume that the s- and r-process contributions are scaled versions of the solar s- and r-process abundances. We quantify the relative fractions of s- and r-process material for each cluster and show that they provide an excellent fit to the observed abundances.
