Washington photometry of candidate star clusters in the Small Magellanic Cloud

Abstract

We present for the first time Washington CT1 photometry for 11 unstudied or poorly studied candidate star clusters. The selected objects are of small angular size, contain a handful of stars, and are projected towards the innermost regions of the Small Magellanic Cloud (SMC). The respective Colour-Magnitude Diagrams (CMDs) were cleaned from the unavoidable star field contamination by taking advantage of a procedure which makes use of variable size Colour-Magnitude Diagram cells. This method has shown to be able to eliminate stochastic effects in the cluster CMDs caused by the presence of isolated bright stars, as well as, to make a finer cleaning in the most populous CMD regions. Our results suggest that nearly 1/3 of the studied candidate star clusters would appear to be genuine physical systems. In this sense, the ages previously derived for some of them mostly reflect those of the composite stellar populations of the SMC field. Finally, we used the spatial distribution in the SMC of possible non-clusters to statistically decontaminate that of the SMC cluster system. We found that there is no clear difference between both expected and observed cluster spatial distributions, although it would become more important at a 2σ level between a ≈ 0.3◦ and 1.2◦ (the semi-major axis of a ellipse parallel to the SMC bar and with b/a = 1/2), if the asterisms were increased up to 20%.