8 research outputs found
Effects of Metallicity on the Rotation Rates of Massive Stars
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 as such 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 V sin
i. 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 V sin i values for 177 O stars. Here we present
complementary V sin i values for 21 Large Magellanic Cloud and 22 Small
Magellanic Cloud O-type stars based on STIS and IUE UV spectroscopy. The
distribution of V sin i 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.Comment: accepted by ApJ, to appear 20 December 2004 editio