Effects of metallicity on the rotational velocities of massive stars.
PENNY L.R., SPRAGUE A.J., SEAGO G. and GIES D.R.
Abstract (from CDS):
Recent theoretical predictions for low-metallicity massive stars predict that these stars should have drastically reduced equatorial winds (mass loss) while on the main sequence, and so should retain most of their angular momentum. Observations of both the Be/(B+Be) ratio and the blue-to-red supergiant ratio appear to have a metallicity dependence that may be caused by high rotational velocities. We have analyzed 39 archival Hubble Space Telescope Imaging Spectrograph (STIS), high-resolution, ultraviolet spectra of O-type stars in the Magellanic Clouds to determine their projected rotational velocities Vsini. Our methodology is based on a previous study of the projected rotational velocities of Galactic O-type stars using International Ultraviolet Explorer (IUE) short-wavelength prime (SWP) camera high-dispersion spectra, which resulted in a catalog of Vsini values for 177 O-type stars. Here we present complementary Vsini values for 21 Large Magellanic Cloud and 22 Small Magellanic Cloud O-type stars based on STIS and IUE UV spectroscopy. The distribution of Vsini values for O-type stars in the Magellanic Clouds is compared to that of Galactic O-type stars. Despite the theoretical predictions and indirect observational evidence for high rotation, the O-type stars in the Magellanic Clouds do not appear to rotate faster than their Galactic counterparts.