Magellanic Clouds

Historically, the wind properties of WR stars have been assumed to be independent of metallicity (Langer 1989), yet there is a well-known observational trend towards later, lower-ionization, WN and WC subtypes at high metallicity, as illustrated in Figure 29.2.

Within the Milky Way, it is well known that late-type WC stars are restricted to within the Solar circle (Conti & Vacca 1990). Indeed, Hopewell et al. (2005)

Wavelength (A)

Figure 29.3. Optical WHT/ISIS spectroscopy of representative WC stars in M31.

Wavelength (A)

Figure 29.3. Optical WHT/ISIS spectroscopy of representative WC stars in M31.

discovered five new WR stars in the inner Milky Way using the AAO/UKST Ha survey - all were found to be WC9 stars.

In addition, Westerlund 1 (Clark et al. 2005) - located at the edge of the Galactic bar, for which a metallicity ~60% higher than that of Orion is expected - possesses eight WC stars with a bias towards late (WC8-9) subtypes according to recent near-IR spectroscopy (Crowther et al. 2006). Most of these possess hot dust, indicative of massive binaries, in common with the Quintuplet members of the Galactic Centre Quintuplet cluster (Figer, private communication). Early-type WN stars are also absent from Westerlund 1, with equal numbers of mid (WN5-6) and late (WN7-10) subtypes, of which most also appear to be massive binaries, as a result of hard X-ray fluxes.

Was this article helpful?

0 0

Post a comment