STIS spectroscopy of newborn massive stars in SMC N81

Using Hubble Space Telescope observations with STIS, we study the main exciting stars of N81, a high excitation compact H ii region in the Small Magellanic Cloud (SMC). These far UV observations are the first spectroscopic measurements of stars in such a region and reveal features characteristic of an O6–O8 stellar type. The astonishing weakness of their wind profiles and their sub-luminosity (up to ~2 mag fainter in MV than the corresponding dwarfs) make these stars a unique stellar population in the Magellanic Clouds. Our analysis suggests that they are probably in the Hertzsprung-Russell diagram locus of a particularly young class of massive stars, the so-called Vz luminosity class, as they are arriving at the zero age main sequence.