We report the discovery of a population of Wolf-Rayet stars in the young Galactic open cluster Westerlund 1. In an incomplete shallow spectro-scopic survey, we find six nitrogen-rich (WN) and five carbon-rich (WC) WR stars. We also confirm the presence of a large population of yellow supergiants, some of which are candidate hypergiants. Given this population, Westerlund 1 is likely to be one of...

A quantitative spectral analysis of 24 A supergiants in the Sculptor Group spiral galaxy NGC 300 at a distance of 1.9 Mpc is presented. A new method is introduced to analyze low resolution (∼ 5Å) spectra, which yields metallicities accurate to 0.2 dex including the uncertainties arising from the errors in Teff (5%) and log g (0.2 dex). For the first time the stellar metallicity gradient based o...

The luminosity of the famous red supergiant VY CMa ( L ∼ 4− 5× 105L⊙) is well-determined from its spectral energy distribution and distance, and places it near the empirical upper luminosity limit for cool hypergiants. In contrast, its surface temperature is fundamentally ill-defined. Both contradict a recent paper by Massey, Levesque and Plez (2006). Implications for its location on the HR Dia...

The diffuse galactic gamma-ray spectrum measured by the EGRET experiment (Hunter et al. 1997) are interpreted within a scenario in which cosmic rays (CRs) are injected by three different kind of sources, (i) supernovae (SN) which explode into the interstellar medium (ISM), (ii) Red Supergiants (RSG), and (iii) Wolf-Rayet stars (WR), where the two latter explode into their pre-SN winds (Biermann...