- ID:
- ivo://CDS.VizieR/J/A+A/653/A13
- Title:
- Lithium in NGC 2243 and NGC 104
- Short Name:
- J/A+A/653/A13
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- We aim to determine the initial Li content of two clusters of similar metallicity but very different age, the old open cluster NGC 2243 and the metal-rich globular cluster NGC 104. We compare the lithium abundances derived for a large sample of stars (from the turn-off to the red giant branch) in each cluster. For NGC 2243, the Li abundances are taken from the catalogues released by the Gaia-ESO Public Spectroscopic Survey, while for NGC 104 we measured the Li abundance using FLAMES/GIRAFFE spectra, which include both archival data and new observations.
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- ID:
- ivo://CDS.VizieR/J/A+A/657/A33
- Title:
- Lithium in the LRGB of 5 globular clusters
- Short Name:
- J/A+A/657/A33
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Lithium is one of the few elements produced during the Big Bang Nucleosynthesis in the early universe. Moreover, its fragility makes it useful as a proxy for stellar environmental conditions. As such, the lithium abundance in old systems is at the core of different astrophysical problems. Stars in the lower red giant branch allow studying globular clusters where main sequence stars are too faint to be observed. We use these stars to analyze the initial Li content of the clusters and compare it to cosmological predictions, to measure spreads in Li between different stellar populations, and to study signs of extra depletion in these giants.
- ID:
- ivo://CDS.VizieR/J/ApJ/819/135
- Title:
- Lithium-rich giants in globular clusters
- Short Name:
- J/ApJ/819/135
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Although red giants deplete lithium on their surfaces, some giants are Li-rich. Intermediate-mass asymptotic giant branch (AGB) stars can generate Li through the Cameron-Fowler conveyor, but the existence of Li-rich, low-mass red giant branch (RGB) stars is puzzling. Globular clusters are the best sites to examine this phenomenon because it is straightforward to determine membership in the cluster and to identify the evolutionary state of each star. In 72 hours of Keck/DEIMOS exposures in 25 clusters, we found four Li-rich RGB and two Li-rich AGB stars. There were 1696 RGB and 125 AGB stars with measurements or upper limits consistent with normal abundances of Li. Hence, the frequency of Li-richness in globular clusters is (0.2+/-0.1)% for the RGB, (1.6+/-1.1)% for the AGB, and (0.3+/-0.1)% for all giants. Because the Li-rich RGB stars are on the lower RGB, Li self-generation mechanisms proposed to occur at the luminosity function bump or He core flash cannot explain these four lower RGB stars. We propose the following origin for Li enrichment: (1) All luminous giants experience a brief phase of Li enrichment at the He core flash. (2) All post-RGB stars with binary companions on the lower RGB will engage in mass transfer. This scenario predicts that 0.1% of lower RGB stars will appear Li-rich due to mass transfer from a recently Li-enhanced companion. This frequency is at the lower end of our confidence interval.
- ID:
- ivo://CDS.VizieR/J/AJ/153/154
- Title:
- LMC NIR survey. IV. Type II Cepheid variables
- Short Name:
- J/AJ/153/154
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present time-series observations of Population II Cepheids in the Large Magellanic Cloud at near-infrared (JHK_s_) wavelengths. Our sample consists of 81 variables with accurate periods and optical (VI) magnitudes from the OGLE survey, covering various subtypes of pulsators (BL Herculis, W Virginis, and RV Tauri). We generate light-curve templates using high-quality I-band data in the LMC from OGLE and K_s_-band data in the Galactic bulge from VISTA Variables in Via Lactea survey (2010NewA...15..433M) and use them to obtain robust mean magnitudes. We derive period-luminosity (P-L) relations in the near-infrared and Period-Wesenheit (P-W) relations by combining optical and near-infrared data. Our P-L and P-W relations are consistent with published work when excluding long-period RV Tauris. We find that Pop II Cepheids and RR Lyraes follow the same P-L relations in the LMC. Therefore, we use trigonometric parallax from the Gaia DR1 (Cat. I/337) for VY Pyx and the Hubble Space Telescope parallaxes for k Pav and 5 RR Lyrae variables to obtain an absolute calibration of the Galactic K_s_-band P-L relation, resulting in a distance modulus to the LMC of {mu}_LMC_=18.54+/-0.08 mag. We update the mean magnitudes of Pop II Cepheids in Galactic globular clusters using our light-curve templates and obtain distance estimates to those systems, anchored to a precise late-type eclipsing binary distance to the LMC. We find that the distances to these globular clusters based on Pop II Cepheids are consistent (within 2{sigma}) with estimates based on the M_V_-[Fe/H] relation for horizontal branch stars.
- ID:
- ivo://CDS.VizieR/J/AJ/142/48
- Title:
- LMC star clusters structural parameters
- Short Name:
- J/AJ/142/48
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present and analyze the radial luminosity profiles of a sample of 1066 stellar clusters in the Large Magellanic Cloud (LMC). By design, this study closely follows the compilation by Hill & Zaritsky (2006, Cat. J/AJ/131/414 of the structural parameters of stellar clusters in the Small Magellanic Cloud (SMC). Both King and Elson-Fall-Freeman model profiles are fit to V-band surface brightness profiles measured from the Magellanic Cloud Photometric Survey images. We tabulate the concentration, central surface brightness, tidal radii, 90% enclosed luminosity radii (r_90_), and local background luminosity density. Over two-thirds of the clusters in the sample are adequately fit by one or both of these models. One notable and systematic exception, as in the SMC, is those clusters that lack a central brightness concentration, the "ring" clusters. While the bulk properties of the clusters are similar between the LMC and SMC populations, we find that the LMC lacks clusters that are as large, either in terms of core radii or r90, as the largest in the SMC, perhaps a signature of larger tidal stresses in the LMC.
- ID:
- ivo://CDS.VizieR/J/ApJ/690/512
- Title:
- LMXBs and globulars in early-type galaxies. II.
- Short Name:
- J/ApJ/690/512
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an astrometry and photometry catalogue of globular cluster (GC) candidates detected with the Hubble Space Telescope Wide Field Planetary Camera 2 in a sample of 19 early-type galaxies, appropriate for comparison with the low-mass X-ray binary populations observed with Chandra. In a companion paper (Cat. J/ApJ/689/983), we present the Chandra data and investigate the relation between these populations. We demonstrate that, although there is little evidence of a color-magnitude correlation for the GCs, after estimating mass and metallicity from the photometry under the assumption of a single-age simple stellar population, there is a significant positive correlation between mass and metallicity.
- ID:
- ivo://CDS.VizieR/J/A+A/533/A33
- Title:
- LMXBs detected in nearby galaxies
- Short Name:
- J/A+A/533/A33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Based on the archival data from the Chandra observations of nearby galaxies, we study different sub populations of low-mass X-ray binaries (LMXBs) - dynamically formed systems in globular clusters (GCs) and in the nucleus of M 31 and (presumably primordial) X-ray binaries in the fields of galaxies. Our aim is to produce accurate luminosity distributions of X-ray binaries in different environments, suitable for quantitative comparison with each other and with the output of population synthesis calculations. Our sample includes seven nearby galaxies (M 31, Maffei 1, Centaurus A, M 81, NGC 3379, NGC 4697, and NGC 4278) and the Milky Way, which together provide relatively uniform coverage down to the luminosity limit of 10^35^erg/s. In total we have detected 185 LMXBs associated with GCs, 35 X-ray sources in the nucleus of M 31, and 998 field sources of which ~365 are expected to be background AGN. We combine these data, taking special care to accurately account for X-ray and optical incompleteness corrections and the removal of the contamination from the cosmic X-ray background sources, to produce luminosity distributions of X-ray binaries in different environments to far greater accuracy than has been obtained previously.
- ID:
- ivo://CDS.VizieR/J/ApJ/662/525
- Title:
- LMXBs in globular clusters of 5 galaxies
- Short Name:
- J/ApJ/662/525
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of LMXBs and GCs in five early-type galaxies using Chandra X-ray and HST optical data. Of the 186 LMXBs within the optical fields of view, 71 are in GCs, confirming that LMXBs are formed particularly efficiently in clusters due to dynamical interactions.
- ID:
- ivo://CDS.VizieR/J/ApJ/663/1021
- Title:
- Log of {omega} Cen scientific images
- Short Name:
- J/ApJ/663/1021
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a photometric investigation on HB, RGB, and MSTO stars in omega Cen = NGC 5139. The center of the cluster was covered with a mosaic of F435W, F625W, and F658N band data collected with HST ACS. The outer reaches were covered with a mosaic of U-, B-, V-, and I-band data collected with the 2.2 m ESO/MPI telescope. The final catalog includes ~1.7 million stars. We identified more than 3200 likely HB stars, the largest sample ever collected in a globular cluster.
- ID:
- ivo://CDS.VizieR/J/A+A/585/A111
- Title:
- Long period variables in omega Cen
- Short Name:
- J/A+A/585/A111
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent studies have detected multiple populations in globular clusters. The massive globular cluster {omega} Cen hosts at least three populations of different metallicity. The most metal-rich one is thought to show also an overabundance of He. These differences should become visible in the structure, evolution, and pulsation of its stars. We aim to study the effects of the different starting compositions of the three populations in {omega} Cen on the most luminous red giants in this cluster. The long-periodic variability of evolved stars in {omega} Cen opens a comparably easy access window to the structure and composition of these objects. We made a detailed search for long-period variables (LPVs) in {omega} Cen leading to the detection of many new variables and period determinations for a significant number of them. Periods and luminosities were then compared with the most recent pulsation models for these kinds of stars.
