STIS spectroscopy of newborn massive stars in SMC N81^*

¹ , Observatoire de Paris, 61 avenue de l'Observatoire, 75014 Paris, France
² Space Telescope European Coordinating Facility, European Southern Observatory, Karl-Schwarzschild-, 85748 Garching bei München, Germany
³ Laboratoire d'Astrophysique, Observatoire Midi-Pyrénées, 14 avenue É. Belin, 31400 Toulouse, France
⁴ Cornell University, Astronomy Department, 106 Space Sciences Bldg., Ithaca, NY 14853, USA

Corresponding author: M. Heydari-Malayeri, heydari@obspm.fr

Received: 14 August 2001
Accepted: 25 October 2001

Abstract

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 M_V 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.