Another relic bulge globular cluster: ESO 456-SC38 (Djorgovski 2)

Autor(es)

Ortolani, S. ^{[1, 2]} ; Held, V, E. ; Nardiello, D. ^[3] ; Souza, S. O. ^[4] ; Barbuy, B. ^[4] ; Perez-Villegas, A. ^[4] ; Cassisi, S. ^{[5, 6]} ; Bica, E. ^[7] ; Momany, Y. ^[3] ; Saviane, I ^[8]

Afiliação do(s) autor(es)

^[1] INAF, Osservatorio Astron Padova, Vicolo Osservatorio 5, I-35122 Padua - Italy

^[2] Univ Padua, Dipartimento Fis & Astron Galileo Galilei, Vicolo Osservatorio 2, I-35122 Padua - Italy

^[3] Held, E., V, INAF, Osservatorio Astron Padova, Vicolo Osservatorio 5, I-35122 Padua - Italy

^[4] Univ Sao Paulo, IAG, Rua Matao 1226, Cidade Univ, BR-05508900 Sao Paulo - Brazil

^[5] INAF, Osservatorio Astron Abruzzo, Via M Maggini Sn, I-64100 Teramo - Italy

^[6] Ist Nazl Fis Nucl, Sez Pisa, Largo Pontecorvo 3, I-56127 Pisa - Italy

^[7] Univ Fed Rio Grande do Sul, Dept Astron, CP 15051, BR-91501970 Porto Alegre, RS - Brazil

^[8] European Southern Observ, Alonso de Cordova 3107, Santiago - Chile

• Tipo de documento: Artigo Científico
• Fonte: Astronomy & Astrophysics; v. 627, JUL 16 2019.
• Citações Web of Science: 1

Resumo

Context. The object ESO 456-SC38 (Djorgovski 2) is one of the globular clusters that is closest to the Galactic center. It is on the blue horizontal branch and has a moderate metallicity of {[}Fe/H] similar to -1.0. It is thus similar to the very old inner bulge globular clusters NGC 6522, NGC 6558, and HP 1, and therefore appears to be part of the primeval formation stages of the Milky Way. Aims. The aim of this work is to determine an accurate distance and metallicity for ESO 456-SC38, as well as orbital parameters, in order to check similarities with other clusters in the inner bulge that have previously been well studied in terms of spectroscopy and photometry. This is a considerably fainter cluster that is contaminated by a rich stellar field; it is also quite absorbed by the dusty foreground. Methods. We analyzed ESO 456-SC38 based on HST photometry, with the filters F606W from ACS, F110W and F160W from WFC3, and photometry in V and I from FORS2 at the VLT. We combined this with identified stars that are covered by Gaia Data Release 2. Results. The isochrone fitting was carried out with the statistical Markov chain Monte Carlo method. We derive an accurate distance of d(circle dot) = 8.75 +/- 0.12 kpc and a reddening of E(B-V) = 0.81(-0.02)(+0.02). The best-fitting BaSTI isochrones correspond to an age of 12.70(-0.69)(+0.72) Gyr and a metallicity of {[}Fe/H] = -1.11(-0.03)(+0.03). Conclusions. ESO 456-SC38 adds to the list of moderately metal-poor globular clusters located in the inner bulge. It has a blue horizontal branch and is very old. The cluster is confined to the bulge and bar region, but it does not support the Galactic bar structure. The old stellar population represented by clusters like this has to be taken into account in models of Galactic bulge formation. Studying them also provides indications on the formation times of the globular clusters themselves. (AU)

• Processo FAPESP: 17/15893-1 - Órbitas de aglomerados globulares do bojo: formação e evolução da Via Láctea
• Beneficiário: Maria de Los Angeles Perez Villegas
• Modalidade de apoio: Bolsas no Brasil - Pós-Doutorado
• Processo FAPESP: 18/22044-3 - Aglomerados globulares do bojo: relíquias da formação e evolução da galáxia
• Beneficiário: Stefano Oliveira de Souza
• Modalidade de apoio: Bolsas no Brasil - Doutorado Direto