The initial mass function of the stellar association NGC 602 in the Small Magellanic Cloud with Hubble Space Telescope ACS observations

We present our photometric study of the stellar association NGC 602 in the wing of the Small Magellanic Cloud (SMC). The data were taken in the filters F555W and F814W using the Advanced Camera for Surveys (ACS) on board the Hubble Space Telescope (HST). Photometry was performed using the ACS module of the stellar photometry package DOLPHOT. We detected more than 5500 stars with a magnitude range of 14 less than or similar to m(555) less than or similar to 28 mag. Three prominent stellar concentrations are identified with star counts in the observed field, the association NGC 602 itself, and two clusters, one of them not being currently in any known catalog. The color-magnitude diagrams ( CMDs) of both clusters show features typical for young open clusters, while that of the association reveals bright main-sequence ( MS) and faint pre-main-sequence (PMS) stars as the members of the system. We construct the initial mass spectrum (IMS) of the association by applying an age-independent method of counting the PMS stars within evolutionary tracks, while for the bright MS stars we transform their magnitudes to masses with the use of mass-luminosity relations. The IMS of NGC 602 is found to be well represented by a single power law, corresponding to an initial mass function (IMF) of slope Gamma approximate to -1.2 for 1 less than or similar to M/M-circle dot less than or similar to 45. This indicates that the shape of the IMF of a star-forming system in the SMC for stars with masses higher than 1 M-circle dot seems to be quite similar to the field IMF in the solar neighborhood.