HST study of the Stellar Populations within 30 pc of SN 1987A

Abstract

We have studied the stellar populations in a region of 30 pc around SN 1987A in the Large Magellanic Cloud using multi-band HST-WFPC2 images. The effective temperature, luminosity and reddening of each detected star were determined by fitting the measured broad band magnitudes to the ones calculated with model atmospheres. The resulting HR diagram reveals the presence of stars with ages between 1 and 150 Myrs, superposed on a much older field population. The youngest stars in the field appear to be T Tauri stars, characterized by strong Halpha excesses. The Star Formation Rate has increased monotonically in the last 8 Gyrs and the star formation activity is still very high at present. Young stars of low and high mass have different spatial distributions. The latter ones are strongly concentrated in the vicinities of the Supernova, whereas the previous ones are more evenly distributed on the field. Hence, the Mass Function varies on a scale of a few parsecs. However, averaging over the entire area, one can define an Initial Mass Function, well fitted by a power-law with a slope alpha<-2.55. The uncertainty on the IMF due to incompleteness in identifying T Tauri stars is discussed.