Washington photometry of 14 intermediate- to old-age star clusters in the Small Magellanic Cloud

PIATTI, ANDRÉS; E.; CLARIA OLMEDO, JUAN; BICA, EDUARDO; GEISLER, DOUG; AHUMADA, A.V.; GIRARDI, L.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

WILEY-BLACKWELL PUBLISHING, INC

Año: 2011 vol. 417 p. 1559 - 1575

0035-8711

We present CCD photometry in the Washington system C, T 1 and T 2 passbands down toT 1 ∼ 23 in the fields of L3, L28, HW 66, L100, HW 79, IC 1708, L106, L108, L109, NGC 643,L112, HW 84, HW 85 and HW 86, 14 Small Magellanic Cloud (SMC) clusters, most of thempoorly studied objects. We measured T 1 magnitudes and C − T 1 and T 1 − T 2 colours for a totalof 213 516 stars spread throughout cluster areas of 14.7 × 14.7 arcmin2 each. We carried outan 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 bythe Padova group to the (T 1 , C − T 1 ) CMDs, as well as from the δ(T 1 ) index and the standardgiant branch procedure, we derived ages and metallicities for the cluster sample. With theexception of IC 1708, a relatively metal-poor Hyades-age cluster, the remaining 13 objects arebetween intermediate and old age (from 1.0 to 6.3 Gyr), their [Fe/H] values ranging from −1.4to −0.7 dex. By combining these results with others available in the literature, we compiled asample of 43 well-known SMC clusters older than 1 Gyr, with which we produced a revisedage distribution. We found that the present clusters’ age distribution reveals two primaryexcesses of clusters at t ∼ 2 and 5 Gyr, which engraves the SMC with clear signs of enhancedformation episodes at both ages. In addition, we found that from the birth of the SMC clustersystem until approximately the first 4 Gyr of its lifetime, the cluster formation resembles thatof a constant formation rate scenario.