- ID:
- ivo://CDS.VizieR/J/A+A/604/A35
- Title:
- NGC104 RGB Na, Mg, and K abundances
- Short Name:
- J/A+A/604/A35
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the abundances of Na, Mg, and K in the atmospheres of 32 red giant branch (RGB) stars in the Galactic globular cluster (GGC) 47 Tuc, with the goal to investigate the possible existence of Na-K and Mg-K correlations/anti-correlations, similar to those that were recently discovered in two other GGCs, NGC 2419 and 2808. The abundances of K, Na, and Mg were determined using high-resolution 2df spectra obtained with the Anglo-Australian Telescope (AAT). The 1D NLTE abundance estimates were obtained using 1D hydrostatic ATLAS9 model atmospheres and spectral line profiles synthesized with the MULTI package. We also used 3D hydrodynamical CO5BOLD and 1D hydrostatic LHD model atmospheres to compute 3D-1D LTE abundance corrections, Delta 3D-1D LTE, for the spectral lines of Na, Mg, and K used in our study. These abundance corrections were used to understand the role of convection in the formation of spectral lines, as well as to estimate the differences in the abundances obtained with the 3D hydrodynamical and 1D hydrostatic model atmospheres. The average element-to-iron abundance ratios and their RMS variations due to star-to-star abundance spreads determined in our sample of RGB stars were <[Na/Fe]>(1D-NLTE)=0.42+/-0.13, <[Mg/Fe]>(1D-NLTE)=0.41+/-0.11, and <[K/Fe]>(1D-NLTE)=0.05+/-0.14. We found no statistically significant relations between the abundances of the three elements studied here. Also, there were no abundance trends with the distance from the cluster center, nor any statistically significant relations between the abundance/abundance ratios and absolute radial velocities of individual stars. All these facts suggest the similarity of K abundance in stars that belong to different generations in 47 Tuc which, in turn, may hint that evolution of K in this particular cluster was unrelated to the nucleosynthesis of Na and/or Mg.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/559/A101
- Title:
- NGC6656 spectroscopy of 71 blue HB stars
- Short Name:
- J/A+A/559/A101
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent investigations revealed very peculiar properties of blue horizontal branch (HB) stars in {omega} Centauri, which show anomalously low surface gravity and mass compared to other clusters and to theoretical models. {omega} Centauri, however, is a very unusual object, hosting a complex mix of multiple stellar populations with different metallicity and chemical abundances. We measured the fundamental parameters (temperature, gravity, and surface helium abundance) of a sample of 71 blue HB stars in M 22, with the aim of clarifying if the peculiar results found in {omega} Cen are unique to this cluster. M 22 also hosts multiple sub-populations of stars with a spread in metallicity, analogous to {omega} Cen.
- ID:
- ivo://CDS.VizieR/J/A+A/588/A148
- Title:
- NGC 6397 stars MUSE spectra
- Short Name:
- J/A+A/588/A148
- Date:
- 23 Mar 2022 16:26:54
- Publisher:
- CDS
- Description:
- We demonstrate the high multiplex advantage of crowded field 3D spectroscopy with the new integral field spectrograph MUSE by means of a spectroscopic analysis of more than 12000 individual stars in the globular cluster NGC 6397. The stars are deblended with a point spread function fitting technique, using a photometric reference catalogue from HST as prior, including relative positions and brightnesses. This catalogue is also used for a first analysis of the extracted spectra, followed by an automatic in-depth analysis via a full-spectrum fitting method based on a large grid of PHOENIX spectra. We analysed the largest sample so far available for a single globular cluster of 18 932 spectra from 12 307 stars in NGC 6397. We derived a mean radial velocity of v_rad_=17.84+/-0.07km/s and a mean metallicity of [Fe/H]=-2.120+/-0.002, with the latter seemingly varying with temperature for stars on the red giant branch (RGB). We determine Teff and [Fe/H] from the spectra, and log g from HST photometry. This is the first very comprehensive Hertzsprung-Russell diagram (HRD) for a globular cluster based on the analysis of several thousands of stellar spectra, ranging from the main sequence to the tip of the RGB. Furthermore, two interesting objects were identified; one is a post-AGB star and the other is a possible millisecond-pulsar companion.
- ID:
- ivo://CDS.VizieR/J/A+A/631/A14
- Title:
- NGC 2808 stellar population spectra
- Short Name:
- J/A+A/631/A14
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Galactic globular clusters (GCs) are now known to host multiple populations displaying particular abundance variations. The different populations within a GC can be well distinguished following their position in the pseudo two-colors diagrams, also referred to as "chromosome maps". These maps are constructed using optical and near-UV photometry available from the Hubble Space Telescope (HST) UV survey of GCs. However, the chemical tagging of the various populations in the chromosome maps is hampered by the fact that HST photometry and elemental abundances are both available only for a limited number of stars. The spectra collected as part of the MUSE survey of globular clusters provide a spectroscopic counterpart to the HST photometric catalogs covering the central regions of GCs. In this paper, we use the MUSE spectra of 1155 red giant branch (RGB) stars in NGC 2808 to characterize the abundance variations seen in the multiple populations of this cluster. We use the chromosome map of NGC 2808 to divide the RGB stars into their respective populations. We then combine the spectra of all stars belonging to a given population, resulting in one high signal-to-noise ratio spectrum representative of each population. Variations in the spectral lines of O, Na, Mg, and Al are clearly detected among four of the populations. In order to quantify these variations, we measured equivalent width differences and created synthetic populations spectra that were used to determine abundance variations with respect to the primordial population of the cluster. Our results are in good agreement with the values expected from previous studies based on high-resolution spectroscopy. We do not see any significant variations in the spectral lines of Ca, K, and Ba. We also do not detect abundance variations among the stars belonging to the primordial population of NGC 2808.
- ID:
- ivo://CDS.VizieR/J/AJ/141/81
- Title:
- NGC 2419 variable star population
- Short Name:
- J/AJ/141/81
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present B, V, and I CCD light curves for 101 variable stars belonging to the globular cluster NGC 2419, 60 of which are new discoveries, based on data sets obtained at the Telescopio Nazionale Galileo, the Subaru telescope, and the Hubble Space Telescope. The sample includes 75 RR Lyrae stars (38 RRab, 36 RRc, and one RRd), one Population II Cepheid, 12 SX Phoenicis variables, two delta Scuti stars, three binary systems, five long-period variables, and three variables of uncertain classification.
- ID:
- ivo://CDS.VizieR/J/AcA/66/31
- Title:
- NGC 3201 variable stars in NGC 3201
- Short Name:
- J/AcA/66/31
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- The field of the globular cluster NGC 3201 was monitored between 1998 and 2009 in a search for variable stars. BV light curves were obtained for 152 periodic or likely periodic variables, fifty-seven of which are new detections. Thirty-seven newly detected variables are proper motion members of the cluster. Among them we found seven detached or semi-detached eclipsing binaries, four contact binaries, and eight SX Phe pulsators. Four of the eclipsing binaries are located in the turnoff region, one on the lower main sequence and the remaining two slightly above the subgiant branch. Two contact systems are blue stragglers, and another two reside in the turnoff region. In the blue straggler region a total of 266 objects were found, of which 140 are proper motion (PM) members of NGC 3201, and another nineteen are field stars. Seventy-eight of the remaining objects for which we do not have PM data are located within the half-light radius from the center of the cluster, and most of them are likely genuine blue stragglers. Four variable objects in our field of view were found to coincide with X-ray sources: three chromospherically active stars and a quasar at a redshift z~~0.5.
- ID:
- ivo://CDS.VizieR/J/MNRAS/499/4026
- Title:
- NGC 6254 variable stars VI light curves
- Short Name:
- J/MNRAS/499/4026
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Time-series VI CCD photometry of the globular cluster M10 (NGC 6254) is employed to perform a detailed identification, inspection of their light curves, their classification and their cluster membership, of all the known variables reported up to 2018. The membership analysis is based on the Gaia-DR2 positions and proper motions. The metallicity of the cluster is estimated based on the sole RRc star known in the cluster. The Fourier decomposition of its light curve leads to [Fe/H]_ZW_=-1.59+/-0.23dex. The mean cluster distance, estimated by several independent methods is 5.0+/-0.3kpc. A multi-approach search in a region of about 10x10arcmin^2^ around the cluster revealed three new variables, one SX Phe (V35) and two sinusoidal variables on the red giant branch of unclear classification (V36,V37). Modelling the HB stars is very sensitive to the stellar hydrogen shell mass, which surrounds the 0.50M_{sun}_ helium core. To match the full stretch of the HB population, a range of total mass of 0.56 to 0.62M_{sun}_ is required. These models support a distance of 5.35kpc and an age of about 13Gyrs, and hints to some individual variation of the mass loss on the upper RGB, perhaps caused by the presence of closed magnetic field in red giants.
- ID:
- ivo://CDS.VizieR/J/MNRAS/493/1996
- Title:
- NGC 6712 variable stars VI light curves
- Short Name:
- J/MNRAS/493/1996
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of VI CCD time-series photometry of globular cluster NGC 6712. Our main goal is to study the variable star population as indicators of the cluster mean physical parameters. We employed the Fourier decomposition of RR Lyrae light curves to confirm that [Fe/H]_UVES_=-1.0+/-0.05 is a solid estimate. We estimated the reddening to the cluster as E(B-V)=0.35+/-0.04 from the RRab stars colour curves. The distance to the cluster was estimated using three independent methods which yielded a weighted mean distance <d>=8.1+/-0.2kpc. The distribution of RRab and RRc stars on the horizontal branch shows a clear segregation around the first overtone red edge of the instability strip, which seems to be a common feature in OoI-type cluster with a very red horizontal branch. We carried out a membership analysis of 60447 stars in our field of view (FoV) using the data from Gaia-DR2 and found 1529 likely members; we possess the light curves of 1100 among the member stars. This allowed us to produce a clean colour-magnitude diagram, consistent with an age of 12Gyr, and enabled us to discover close unresolved contaminants for several variable stars. From the proper motion analysis, we found evidence of non-member stars in the FoV of the cluster being tidally affected by the gravitational pull of the bulge of the Galaxy. We found that the RRab variable V6, shows a previously undetected Blazhko effect. Finally, we report 16 new variables of the EW-type (9) and SR-type (7).
- ID:
- ivo://CDS.VizieR/J/other/RMxAA/55.337
- Title:
- NGC 1261 variables VI light curves
- Short Name:
- J/other/RMxAA/55
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Time-series VI CCD photometry of the globular cluster NGC 1261 is employed to study its variable star population. A membership analysis of most variables based on Gaia DR2 proper motions and colours was performed prior to the estimation of the mean cluster distance and metallicity. The light curves of the member RR Lyrae were Fourier decomposed to calculate their individual values of distance, [Fe/H], radius and mass. The I-band P-L for RR Lyrae stars was also employed. Our best estimates of the metallicity and distance of this Oo I cluster are [Fe/H]_ZW_=-1.42+/-0.05dex and d=17.2+/-0.4kpc. No mixture of fundamental and first overtone RR Lyrae stars in the either-or or bimodal region is seen in this cluster, as it seems to be the rule for Oo I clusters with a red horizontal branch. A multi-approach search in a region of about 10x10 arcmin^2^ around the cluster revealed no new variable stars within the limitations of our CCD photometry.
- ID:
- ivo://CDS.VizieR/J/MNRAS/452/727
- Title:
- NGC 6229 variable VI light curves
- Short Name:
- J/MNRAS/452/727
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report an analysis of new V and I CCD time series photometry of the distant globular cluster NGC 6229. The principal aims were to explore the field of the cluster in search of new variables, and to Fourier decompose the RR Lyrae light curves in pursuit of physical parameters. We found 25 new variables: 10 RRab, 5 RRc, 6 SR, 1 CW, 1 SX Phe, and 2 that we were unable to classify. Secular period changes were detected and measured in some favourable cases. The classifications of some of the known variables were rectified. The Fourier decomposition of RRab and RRc light curves was used to independently estimate the mean cluster value of [Fe/H] and distance. From the RRab stars we found [Fe/H]_UVES_ =-1.31+/-0.01(statistical)+/-0.12(systematic) ([Fe/H]_ZW_=-1.42) and a distance of 30.0+/-1.5kpc, and from the RRc stars we found [Fe/H]_UVES_=-1.29+/-0.12 and a distance of 30.7+/-1.1kpc, respectively. Absolute magnitudes, radii and masses are also reported for individual RR Lyrae stars. Also discussed are the independent estimates of the cluster distance from the tip of the red giant branch, 34.9+/-2.4kpc and from the period-luminosity relation of SX Phe stars, 28.9+/-2.2kpc. The distribution of RR Lyrae stars in the horizontal branch shows a clear empirical border between stable fundamental and first overtone pulsators which has been noted in several other clusters; we interpret it as the red edge of the first overtone instability strip.
