Self-consistent physical parameters for five intermediate-age SMC stellar clusters from CMD modelling⋆,⋆⋆,⋆⋆⋆
Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de
São Paulo, Rua do Matão 1226, Cidade Universitária,
2 European Southern Observatory, Alonso de Cordova 3107, Santiago, Chile
3 LATO-DCET-UESC, Rodovia Ilhéus-Itabuna km 16, Ilhéus, Bahia 45662-000, Brazil
4 Universidade Federal do Rio Grande do Sul, IF, CP 15051, 91501-970, RS, Porto Alegre, Brazil
5 Dipartimento di Fisica e Astronomia Galileo Galilei, University of Padova, vicolo dell’Osservatorio 3, 35122 Padova, Italy
Accepted: 15 November 2013
Context. Stellar clusters in the Small Magellanic Cloud (SMC) are useful probes for studying the chemical and dynamical evolution of this neighbouring dwarf galaxy, enabling inspection of a large period covering over 10 Gyr.
Aims. The main goals of this work are the derivation of age, metallicity, distance modulus, reddening, core radius, and central density profiles for six sample clusters, in order to place them in the context of the Small Cloud evolution. The studied clusters are AM 3, HW 1, HW 34, HW 40, Lindsay 2, and Lindsay 3; HW 1, HW 34, and Lindsay 2 are studied for the first time.
Methods. Optical colour–magnitude diagrams (V,B − V CMDs) and radial density profiles were built from images obtained with the 4.1 m Southern Astrophysical Research (SOAR) telescope, reaching V ~ 23. The determination of structural parameters were carried out by applying King profile fitting. The other parameters were derived in a self-consistent way by means of isochrone fitting, which uses likelihood statistics to identify the synthetic CMDs that best reproduce the observed ones. Membership probabilities were determined comparing the cluster and control field CMDs. Completeness and photometric uncertainties were obtained by performing artificial star tests.
Results. The results confirm that these clusters (except HW 34, identified as a field fluctuation) are intermediate-age clusters, with ages between 1.2 Gyr (Lindsay 3) and ~5.0 Gyr (HW 1). In particular HW 1, Lindsay 2 and Lindsay 3 are located in a region that we called West Halo, where studies of ages and metallicity gradients are still lacking. Moreover, Lindsay 2 was identified as a moderately metal-poor cluster with [Fe/H] = −1.4 ± 0.2 dex, lower than expected from the age-metallicity relation by Pagel & Tautvaisiene (1998). We also found distances varying from ~53 kpc to 66 kpc, compatible with the large depth of the SMC.
Key words: galaxies: star clusters: general / Magellanic Clouds / Hertzsprung-Russell and C-M diagrams
Based on observations obtained at the Southern Astrophysical Research (SOAR) telescope, which is a joint project of the Ministério da Ciência, Tecnologia, e Inovação (MCTI) da República Federativa do Brasil, the US National Optical Astronomy Observatory (NOAO), the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU).
Appendix A is available in electronic form at http://www.aanda.org
The tables of photometry are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (184.108.40.206) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/561/A106
© ESO, 2014