Evolución química e historia de la formación estelar en el disco de la Nube Mayor de Magallanes

PIATTI, ANDRÉS E.; GEISLER, DOUG; BICA, EDUARDO; CLARIA OLMEDO, JUAN JOSÉ

La Plata

Congreso; Reunión Anual de la Asoc. Argentina de Astronomía; 2003

We present Washington system colour-magnitude diagrams for 8 LMC inner disc star clusters and their surrounding fields. Ages and metallicities are determined for both stellar populations in two different ways: (1) By using theoretical isochrones recently calculated for the Washington system. (2) By using the δT1 parameter defined by Geisler et al. (1997, AJ, 114, 1920) and the standard giant branches of Geisler & Sarajedini (1999, AJ, 117, 308). For this latter metallicity derivation, we present age-dependent metallicity corrections for intermediate-age clusters (IACs). The two methods are in good agreement with each other. All clusters are found to be IACs (1-3 Gyr), with [Fe/H] from -0.2 to -1.0. We find that the stellar population of each star cluster is generally quite similar to that of the field where it is embedded, sharing its mean age and metallicity. Combining the present sample with those obtained for other 30 clusters using the same technique we arrive at the following conclusions: (1) The most recent stellar formation events have occurred in the central part of the LMC. (2) On average, the inner disc star clusters are younger and more metal-rich than the outer disc star ones. (3) The best description of the age- metallicity relationship in the LMC is a bursting formation mechanism, with an important event centred at ˜ 2 Gyr. (4) In the outer disc, the field star formation seems to have lasted until 2 Gyrs ago, while it continued in the inner disc for almost 1 Gyr longer. (5) There exist some evidence of a metal abundance gradient in the LMC disc.