Rapid rotation in Be stars : testing the null hypothesis - Be stars are all 'near-critical' rotators

• Main Author: North, Matthew W. M.
• Published: University College London (University of London) 2008
• Subjects: 520
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.503102

The purpose of this thesis is to test the null hypothesis that all Be stars rotate close to their critical velocities. To do this, a grid of synthetic Be-star spectra is constructed, for Veq/Krit = 0.95, accounting for gravity darkening, limb darkening and viewing angle. This grid explores the full parameter space of the B star domain, subject to a minimum equatorial temperature constraint (TLOCai > 6000i*T), for a range of equatorial rotational velocities. The models are compared to 95 of the 116 Be stars in the Chauville et al. (2001) atlas. Of the stars modelled, 79 are fit acceptably, 12 show minor mismatches, the general cause of which is attributed to the presence of emission in the spectra. The four remaining fits are unacceptable, three due to a high degree of shell spectrum contamination, another as a result of a binary companion. In essence, the null hypothesis is believed to survive. One important implication of this is that velocities on the order of the sound speed are sufficient to promote the formation of Be-star circumstellar disks.