PROPERTIES OF STAR-2, ONE OF THE SN-1987A COMPANIONS, DERIVED FROM HUBBLE-SPACE-TELESCOPE FAINT OBJECT SPECTROGRAPH OBSERVATIONS

We present and discuss the Hubble Space Telescope Faint Object Spectro graph observations of Star 2, one of the two companions of SN 1987A, i n the range 1200-8000 Angstrom. Our analysis, based on a comparison of the observed spectrum with spectra of O and B type stars and with mod el atmospheres, confirms that Star 2 is a B2III star. The extinction t oward Star 2 is mostly of LMC origin and amounts to an E(B-V) = 0.19 /- 0.02. The detailed extinction curve has a 2200 Angstrom bump less p ronounced than the average LMC extinction law. Star 2 has an effective temperature of T-eff = 22,000 +/- 2000 K and a luminosity of log L/L. = 4.38 +/- 0.11. Also, Star 2 appears to rotate with an equatorial ve locity of v sin i = 250 +/- 50 km s(-1) and is presently undergoing ma ss loss at a range of log M similar or equal to 7.0 +/- 0.5 M. yr(-1) Judging from its position in the H-R diagram and its present parameter s, Star 2 had an original mass of about 13 M. and was born less than 1 3 Myr ago, which makes Star 2 coeval to the SN 1987A progenitor Sk 69 degrees 202.