Seven young star clusters in the inner region of the Small Magellanic Cloud

PIATTI, ANDRÉS E.; GEISLER, DOUG; SARAJEDINI, A.; GALLART, C.; WISCHNJEWSKY, M.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

Año: 2008 vol. 389 p. 429 - 440

0035-8711

We present CCD photometry in the Washington system C and T1 passbands down to T1 ~ 22 in the fields of L35, L45, L49, L50, L62, L63, and L85, seven poorly studied star clusters in the inner region of the SMC. We measured T1 magnitudes and C-T1 colours for a total of 114,826 stars distributed throughout cluster areas of 13.7' x 13.7' each. Cluster radii were estimated from star counts distributed throughout the entire observed fields. The seven clusters are generally characterized by a relatively small angular size and by a high field star contamination. We performed an in-depth analysis of the field star contamination of the colour-magnitude diagrams (CMDs), and statistically cleaned the cluster CMDs. Based on the best fits of isochrones computed by the Padova group to the (T1, C-T1) CMDs, we derive ages for the sample, assuming Z = 0.004, finding ages between 25 Myr and 1.2 Gyr.We then examined different relationships between position in the SMC, age and metallicity of a larger sample of clusters including our previous work whose ages and metallicities are on the same scale used in this paper. We confirm previous results in the sense that the further a cluster is from thecentre of  the galaxy, the older and more metal-poor it is, with some dispersion; although clusters associated with the Magellanic bridge clearly do not obey the general trend. The number of clusters within ~ 2° of the SMC centre appears to have increased substantially after ~2.5 Gyr ago, hinting at a burst.