THE COMPLETE INITIAL MASS FUNCTION DOWN TO THE SUBSOLAR REGIME IN THE LARGE MAGELLANIC CLOUD WITH HUBBLE SPACE TELESCOPE ACS OBSERVATIONS

In this photometric study of the stellar association LII 95 in the Large Magellanic Cloud (LMC) we focus on the pre-main-sequence (PMS) population in order to construct, for the first time, the subsolar initial mass function (IMF) in the LMC. The basis for this investigation consists of the deepest photometry ever performed in the LMC with the Advanced Camera for Surveys (ACS) onboard the Hubble Space Telescope. We improve our catalog of point sources obtained with ACS (Paper I). We carry out a Monte Carlo technique to subtract the contribution of the general field of LMC. We isolate the central region in the observed area of the association, as the part characterized by the highest concentration of PMS stars. We analyze the reddening distribution of the system in order to obtain the mean value of extinction and we study the mass function of its field-subtracted population. For this purpose, we introduce a new set of evolutionary models, derived from the calculations on the evolution of PMS stars by Siess and collaborators. We use these models with our observations of LH 95 to derive the IMF of the system. This mass function is reliably constructed for stars with masses down to similar or equal to 0.43 M-circle dot, the lowest mass ever observed within reasonable completeness in the Magellanic Clouds. Consequently, its construction offers an outstanding improvement in our understanding of the low-mass star formation in the LMC. The system IMF of LH 95 shows a definite change in its slope for masses M less than or similar to 1 M-circle dot, where it becomes more shallow. In general, the shape of this IMF agrees very well with a multiple power law, as the typical Galactic IMF, down to the subsolar regime. The change in the slope ("the knee") of our IMF at similar to 1 M-circle dot also agrees with the average Galactic IMF. As far as the slope of this system IMF is concerned, it is found to be somewhat more shallow than the corresponding "classical" Galactic IMF in the subsolar regime, probably due to unresolved binarity, while for stars with M greater than or similar to 1 M-circle dot it becomes slightly steeper. We do not find significant differences in the shape of the overall IMF of LH 95 from that of each of the three individual subclusters of the association. This clearly suggests that the IMF of LH 95 is not subject to local variability.