- ID:
- ivo://CDS.VizieR/J/ApJ/654/915
- Title:
- Deep FORS1 BR photometry of omega Cen
- Short Name:
- J/ApJ/654/915
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a deep photometric survey performed with the VLT FORS1 aimed at investigating the complex main-sequence structure of the stellar system Centauri. We confirm the presence of a double main sequence and identify its blue component (bMS) over a large field of view up to 26' from the cluster center. We found that bMS stars are significantly more concentrated toward the cluster center than the other "normal" MS stars. The bMS morphology and its position in the CMD have been used to constrain the helium overabundance required to explain the observed MS morphology.
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- ID:
- ivo://CDS.VizieR/J/A+AS/82/71
- Title:
- Deep photometry of NGC 5694 and Terzan 8
- Short Name:
- J/A+AS/82/71
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present deep CCD photometries for the little known metal-poor clusters NGC 5694 and Terzan 8 down to V~24. NGC 5694 has a blue horizontal branch, a very high radial velocity, a metallicity of [Fe/H]=-1.65+/-0.06, a reddening of E(B-V)=0.10+/-0.03, and an apparent distance modulus of (m-M)_v_=17.82+/-0.15. It is located at 26.0+/-1.8kpc from the galactic center. The helium content derived from the ratio between the number of stars on the horizontal branch and the giant and asymptotic giant branches is consistent with that obtained for other clusters. Terzan 8 is a metal-poor ([Fe/H]=-1.81+/-0.10) moderately reddened (E(B-V)=0.20+/-0.05) cluster with a blue horizontal branch and apparent distance modulus of (m-M)_v_=17.25+/-0.15. It is located at 13.8+/-2.0 kpc from the galactic center. The c-m diagram and the luminosity function of NGC 5694 and Terzan 8 are similar to the M92 ones. NGC 5694 and Terzan 8 have ages close to that of the "classical" globular cluster M92.
- ID:
- ivo://CDS.VizieR/J/MNRAS/431/1995
- Title:
- Deep uVI photometry of NGC2419
- Short Name:
- J/MNRAS/431/1995
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present accurate wide-field uVI photometry of the remote and massive Galactic globular cluster NGC 2419, aimed at searching for the u-V colour spread along the red giant branch (RGB) which is generally interpreted as the photometric signature of the presence of multiple populations in globular clusters. Focusing on the RGB stars in the magnitude range 19.8<=V<=22.0, we find that (i) the u-V, u-I and the V-I spreads about the RGB ridge line are significantly larger than that expected from observational errors, accurately quantified by means of extensive artificial stars experiments, (ii) the intrinsic colour spreads in u-V and u-I are larger than in V-I, and (iii) the stars lying to the blue of the RGB ridge line in u-V and u-I are significantly more concentrated towards the cluster centre than those lying to the red of that line. All the above observational facts can be interpreted in a scenario where a sizable fraction of cluster stars belong to a second generation heavily enriched in helium. Finally, we find that bright RGB stars (17.5<V<19.0) having [Mg/Fe]<0.0 lie preferentially on the red side of the cluster RGB, while those having [Mg/Fe]>0.0 lie preferentially on the blue side.
- ID:
- ivo://CDS.VizieR/J/MNRAS/443/2492
- Title:
- {Delta}a observations of 3 globular clusters
- Short Name:
- J/MNRAS/443/2492
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Globular clusters are main astrophysical laboratories to test and modify evolutionary models. Thought to be rather homogeneous in their local elemental distribution of members, results suggest a wide variety of chemical peculiarities. Besides different main sequences, believed to be caused by different helium abundances, peculiarities of blue horizontal-branch stars and on the red giant branch were found. This whole zoo of peculiar objects has to be explained in the context of stellar formation and evolution. The tool of {Delta}a photometry is employed in order to detect peculiar stars in the whole spectral range. This three filter narrow-band system measures the flux distribution in the region from 4900 to 5600{AA} in order to find any peculiarities around 5200{AA}. It is highly efficient to detect classical chemically peculiar stars of the upper main sequence, Be/Ae, shell and metal-weak objects in the Milky Way and Magellanic Clouds. We present {Delta}a photometry of 2266 stars from 109 individual frames for three globular clusters (NGC 104, NGC 6205, and NGC 7099). A comparison with published abundances, for three horizontal-branch stars, only, yields an excellent agreement. According to the 3{sigma} detection limit of each globular cluster, about 3 percent of the stars lie in abnormal regions in the diagnostic diagrams. The first observations of three widely different aggregates give very promising results, which will serve as a solid basis for follow-up observations including photometric as well as spectroscopic studies.
- ID:
- ivo://CDS.VizieR/J/MNRAS/449/3889
- Title:
- Detailed abundances of 15 stars in NGC 4833
- Short Name:
- J/MNRAS/449/3889
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have observed 15 red giant stars in the relatively massive, metal-poor globular cluster NGC 4833 using the Magellan Inamori Kyocera Echelle spectrograph at Magellan. We calculate stellar parameters for each star and perform a standard abundance analysis to derive abundances of 43 species of 39 elements, including 20 elements heavier than the iron group. We derive <[Fe/H]>=-2.25+/-0.02 from FeI lines and <[Fe/H]>=-2.19+/-0.013 from FeII lines. We confirm earlier results that found no internal metallicity spread in NGC 4833, and there are no significant star-to-star abundance dispersions among any elements in the iron group (19=<Z=<30). We recover the usual abundance variations among the light elements C, N, O, Na, Mg, Al, and possibly Si. The heavy-element distribution reflects enrichment by r-process nucleosynthesis ([Eu/Fe]=+0.36+/-0.03), as found in many other metal-poor globular clusters. We investigate small star-to-star variations found among the neutron-capture elements, and we conclude that these are probably not real variations. Upper limits on the Th abundance, log{epsilon} (Th/Eu)<-0.47+/-0.09, indicate that NGC 4833, like other globular clusters where Th has been studied, did not experience a so-called actinide boost.
- ID:
- ivo://CDS.VizieR/J/A+A/557/A138
- Title:
- Detailed chemical abundances in the GlC NGC 362
- Short Name:
- J/A+A/557/A138
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We obtained FLAMES GIRAFFE+UVES spectra for both first and second-generation red giant branch (RGB) stars in the globular cluster (GC) NGC 362 and used them to derive abundances of 21 atomic species for a sample of 92 stars. The surveyed elements include proton-capture (O, Na, Mg, Al, Si), alpha-capture (Ca, Ti), Fe-peak (Sc, V, Mn, Co, Ni, Cu), and neutron-capture elements (Y, Zr, Ba, La, Ce, Nd, Eu, Dy). The analysis is fully consistent with that presented for twenty GCs in previous papers of this series. Stars in NGC 362 seem to be clustered into two discrete groups along the Na-O anti-correlation, with a gap at [O/Na]~0dex. Na-rich, second generation stars show a trend to be more centrally concentrated, although the level of confidence is not very high. When compared to the classical second-parameter twin NGC 288, with similar metallicity, but different horizontal branch type and much lower total mass, the proton-capture processing in stars of NGC 362 seems to be more extreme, confirming previous analysis. We discovered the presence of a secondary RGB sequence, redder than the bulk of the RGB: a preliminary estimate shows that this sequence comprises about 6% of RGB stars. Our spectroscopic data and literature photometry indicate that this sequence is populated almost exclusively by giants rich in Ba, and probably rich in all s-process elements, as found in other clusters. In this regards, NGC 362 joins previously studied GCs like NGC 1851, NGC 6656 (M 22), and NGC 7089 (M 2).
- ID:
- ivo://CDS.VizieR/J/A+A/372/85
- Title:
- Detected sources at 12{mu}m in 47 Tuc
- Short Name:
- J/A+A/372/85
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The present paper investigates the properties of the dust mass loss in stars populating the giant branch of the globular cluster 47 Tuc, by combining ISOCAM and DENIS data. Raster maps of 5 fields covering areas ranging from 4x4 to 15x15arcmin^2^ at different distances from the center of the cluster have been obtained with ISOCAM at 11.5{mu}m (LW10 filter). The covered fields include most of the red variables known in this cluster. A detection threshold of about 0.2 mJy is achieved, allowing us to detect giant stars at 11.5{mu}m all the way down to the horizontal branch. No dust-enshrouded asymptotic giant branch stars have been found in the observed fields, contrary to the situation encountered in LMC/SMC globular clusters with larger turnoff masses. The color index [12]-[2] (based on the ISO 11.5{mu}m flux and on the DENIS K_S_ magnitude) is used as a diagnostic of dust emission (and hence dust mass loss). Its evolution with luminosity along the giant branch reveals that dust mass loss is only present in V3 (the only cluster Mira variable observed in the present study) and in V18, a star presenting intermittent variability. This conclusion confirms the importance of stellar pulsations in the dust formation and ensuing mass loss.
- ID:
- ivo://CDS.VizieR/J/MNRAS/386/1443
- Title:
- 2dF study of globular clusters in NGC 5128
- Short Name:
- J/MNRAS/386/1443
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have performed a spectroscopic study of globular clusters (GCs) in the nearest giant elliptical NGC 5128 using the 2dF facility at the Anglo-Australian Telescope. We obtained integrated optical spectra for a total of 254 GCs, 79 of which are newly confirmed on the basis of their radial velocities and spectra. In addition, we obtained an integrated spectrum of the galaxy starlight along the southern major axis.
- ID:
- ivo://CDS.VizieR/J/AJ/151/40
- Title:
- Differential BV photometry of 5 variables in M79
- Short Name:
- J/AJ/151/40
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of a luminous F-type post-asymptotic-giant-branch (PAGB) star in the Galactic globular cluster (GC) M79 (NGC 1904). At visual apparent and absolute magnitudes of V=12.20 and M_V_=-3.46, this "yellow" PAGB star is by a small margin the visually brightest star known in any GC. It was identified using CCD observations in the uBVI photometric system, which is optimized to detect stars with large Balmer discontinuities, indicative of very low surface gravities. Follow-up observations with the SMARTS 1.3 and 1.5m telescopes show that the star is not variable in light or radial velocity, and that its velocity is consistent with cluster membership. Near- and mid-infrared observations with 2MASS and WISE show no evidence for circumstellar dust. We argue that a sharp upper limit to the luminosity function exists for yellow PAGB stars in old populations, making them excellent candidates for Population II standard candles, which are four magnitudes brighter than RR Lyrae variables. Their luminosities are consistent with the stars being in a PAGB evolutionary phase, with core masses of ~0.53M_{sun}_. We also detected four very hot stars lying above the horizontal branch ("AGB-manque" stars); along with the PAGB star, they are the brightest objects in M79 in the near-ultraviolet. In the Appendix, we give periods and light curves for five variables in M79: three RR Lyrae stars, a Type II Cepheid, and a semiregular variable.
- ID:
- ivo://CDS.VizieR/J/AJ/143/70
- Title:
- Differential reddening in Milky Way globulars
- Short Name:
- J/AJ/143/70
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Extensive photometric studies of the globular clusters located toward the center of the Milky Way have been historically neglected. The presence of patchy differential reddening in front of these clusters has proven to be a significant obstacle to their detailed study. We present here a well defined and reasonably homogeneous photometric database for 25 of the brightest Galactic globular clusters located in the direction of the inner Galaxy. These data were obtained in the B, V, and I bands using the Magellan 6.5m Telescope and the Hubble Space Telescope. A new technique is extensively used in this paper to map the differential reddening in the individual cluster fields, and to produce cleaner, dereddened color-magnitude diagrams for all the clusters in the database. Subsequent papers will detail the astrophysical analysis of the cluster populations, and the properties of the obscuring material along the clusters' lines of sight.
