First results from the Goddard High-Resolution Spectrograph: Spectroscopic determination of stellar parameters of Melnick 42, an O3f star in the large magellanic cloud

GHRS and optical (ESO 3.6 m) observations of the O3f star Melnick 42 in the 30 Doradus complex are reported. A first analysis reveals that with a luminosity of 2.3 × 10⁶ L⊙ and a present mass of 100 M⊙, Melnick 42 is one of the most luminous and massive stars known. An estimate of abundances indicates that iron and oxygen are very likely reduced by a factor of 4 relative to the Sun, whereas carbon is more strongly depleted and nitrogen is approximately solar. The terminal velocity of the stellar wind is 3000 km s^-1. The mass-loss rate is 4 × 10^-6 M⊙ yr^-1, with a large uncertainty. The excellent quality GHRS spectrum taken in a crowded region of the LMC demonstrates the superiority of the HST for quantitative ultraviolet spectroscopy of hot stars in other galaxies.