Stellar and wind properties of massive stars in the central parsec of the Galaxy

¹ Max-Planck Institt fr extraterrestrische Physik, Postfach-1312, 85741, Garching, Germany e-mail: martins@mpe.mpg.de
² Department of Physics, University of California, Berkeley, CA 94720, USA
³ Department of Physics and Astronomy, University of Pittsburgh, 3941 O'Hara St., Pittsburgh, PA 15260, USA
⁴ LESIA, Observatoire de Paris, 5 Place Jules Janssen, 92195, Meudon, France

Received: 3 November 2006
Accepted: 1 March 2007

Abstract

Context.How star formation proceeds in the Galactic Center is a debated question. Addressing this question will help us understand the origin of the cluster of massive stars near the supermassive black hole, and more generally, starburst phenomena in galactic nuclei. In that context, it is crucial to know the properties of young massive stars in the central parsec of the Galaxy.

Aims.The main goal of this study is to derive the stellar and wind properties of the massive stars orbiting the supermassive black hole SgrA in two counter-rotating disks.

Methods.We use non-LTE atmosphere models including winds and line-blanketing to reproduce H and K band spectra of these stars obtained with SINFONI on the ESO/VLT.

Results.The GC massive stars appear to be relatively similar to other Galactic stars. The currently known population of massive stars emit a total 6.0  10⁵⁰ s^-1 (resp. 2.3  10⁴⁹ s^-1) H (resp. ) ionising photons. This is sufficient to produce the observed nebular emission and implies that, in contrast to previous claims, no peculiar stellar evolution is required in the Galactic Center. We find that most of the Ofpe/WN9 stars are less chemically evolved than initially thought. The properties of several WN8 stars are given, as well as two WN/C stars confirmed quantitatively to be stars in transition between the WN and WC phase. We propose the sequence (Ofpe/WN9  LBV)  WN8  WN/C for most of the observed GC stars. Quantitative comparison with stellar evolutionary tracks including rotation favour high mass loss rates in the Wolf-Rayet phase in these models. In the OB phase, these tracks nicely reproduce the average properties of bright supergiants in the Galactic Center.