First estimates of the fundamental parameters of three Large Magellanic Cloud clusters

PIATTI, ANDRÉS; E.; CLARIA OLMEDO, JUAN; PARISI, M.C.; AHUMADA, A.V.

PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF THE PACIFIC

UNIV CHICAGO PRESS

Año: 2011 vol. 123 p. 519 - 530

0004-6280

    As part of an ongoing project to investigate the cluster formation and chemicalevolution history in the Large Magellanic Cloud (LMC), we have used the CTIO0.9 m telescope to obtain CCD imaging in the Washington system of NGC 2161,SL 874 and KMHK 1719, three unstudied star clusters located in the outer regionof the LMC. We measured T1 magnitudes and C − T1 colors for a total of 9611stars distributed throughout cluster areas of 13.6x13.6 arcmin2 . Cluster radiiwere estimated from star counts distributed throughout the entire observed fields.Careful attention was paid to setting apart the cluster and field star distributionsso statistically cleaned color-magnitude diagrams (CMDs) were obtained. Basedon the best fits of isochrones computed by the Padova group to the (T1 , C −T1 ) CMDs, the δT1 index and the Standard Giant Branch procedure, ages andmetallicities were derived for the three clusters. The different methods for bothage and metallicity determination are in good agreement. The three clusters werefound to be of intermediate-age (∼ 1 Gyr) and relatively metal-poor ([Fe/H] ∼-0.7 dex). By combining the current results with others available in the literature,a total sample of 45 well-known LMC clusters older than 1 Gyr was compiled. Byadopting an age interval varying in terms of age according to a logarithmic law, webuilt the clusters’ age histogram which statistically represents the intermediate-age and old stellar populations in the LMC. Two main cluster formation episodesthat peaked at t ∼ 2 and ∼ 14 Gyr were detected. The present cluster agedistribution was compared to star formation rates analytically derived in previousstudies.