| Full text | |
| Author(s): |
Kerber, L. O.
[1, 2]
;
Nardiello, D.
[3, 4]
;
Ortolani, S.
[3, 4]
;
Barbuy, B.
[1]
;
Bica, E.
[5]
;
Cassisi, S.
[6]
;
Libralato, M.
[3, 7, 4]
;
Vieira, R. G.
[1]
Total Authors: 8
|
| Affiliation: | [1] Univ Sao Paulo, IAG, Rua Matao 1226, Cidade Univ, BR-05508900 Sao Paulo - Brazil
[2] Univ Estadual Santa Cruz, DCET, Rodovia Jorge Amado Km 16, BR-45662000 Ilheus, BA - Brazil
[3] INAF Osservatorio Astron Padova, Vicolo Osservatorio 5, I-35122 Padua - Italy
[4] Univ Padua, Dipartimento Astron, Vicolo Osservatorio 5, I-35122 Padua - Italy
[5] Univ Fed Rio Grande do Sul, Dept Astron, CP 15051, BR-91501970 Porto Alegre, RS - Brazil
[6] Osservatorio Astron Abruzzo, Via M Maggini Sn, I-64100 Teramo - Italy
[7] Space Telescope Sci Inst, 3700 San Martin Dr, Baltimore, MD 21218 - USA
Total Affiliations: 7
|
| Document type: | Journal article |
| Source: | ASTROPHYSICAL JOURNAL; v. 853, n. 1 JAN 20 2018. |
| Web of Science Citations: | 13 |
| Abstract | |
Bulge globular clusters (GCs) with metallicities {[}Fe/H] less than or similar to -1.0 and blue horizontal branches are candidates to harbor the oldest populations in the Galaxy. Based on the analysis of HST proper-motion-cleaned color-magnitude diagrams in filters F435W and F625W, we determine physical parameters for the old bulge GCs NGC 6522 and NGC 6626 (M28), both with well-defined blue horizontal branches. We compare these results with similar data for the inner halo cluster NGC 6362. These clusters have similar metallicities (-1.3 <= {[}Fe/H] <= -1.0) obtained from high-resolution spectroscopy. We derive ages, distance moduli, and reddening values by means of statistical comparisons between observed and synthetic fiducial lines employing likelihood statistics and the Markov chain Monte Carlo method. The synthetic fiducial lines were generated using alpha-enhanced BaSTI and Dartmouth stellar evolutionary models, adopting both canonical (Y similar to 0.25) and enhanced (Y similar to 0.30-0.33) helium abundances. RR Lyrae stars were employed to determine the HB magnitude level, providing an independent indicator to constrain the apparent distance modulus and the helium enhancement. The shape of the observed fiducial line could be compatible with some helium enhancement for NGC 6522 and NGC 6626, but the average magnitudes of RR Lyrae stars tend to rule out this hypothesis. Assuming canonical helium abundances, BaSTI and Dartmouth models indicate that all three clusters are coeval, with ages between similar to 12.5 and 13.0 Gyr. The present study also reveals that NGC 6522 has at least two stellar populations, since its CMD shows a significantly wide subgiant branch compatible with 14% +/- 2% and 86% +/- 5% for first and second generations, respectively. (AU) | |
| FAPESP's process: | 12/20364-4 - Beyond dust survival: the inner regions of protoplanetary disks |
| Grantee: | Rodrigo Georgetti Vieira |
| Support Opportunities: | Scholarships in Brazil - Post-Doctoral |