Evolution of Galactic Field be Stars

Abstract

Galactic field Be stars were studied by taking into account the effects induced by the fast rotation on their fundamental parameters. Fractional ages $\tau /\tau \_\mathrm{MS}$ ($\tau \_\mathrm{MS}$ = time spent in the MS) against stellar mass reveal that: a) Be stars spread over the whole interval $0<\tau /\tau \_\mathrm{MS}<1$; b) the Be phenomenon in massive stars ($M>12M\_\odot$) is present at smaller age ratios than for less massive stars ($M<12M\_\odot$); c) there is a lack of Be stars with $M<7M\_\odot$ in the first half of the MS. Low mass fast rotators ($M<7M\_\odot$), called Bn stars, could be "becoming" Be stars.

Societe Francaise d'Astronomie et d'Astrophysique, France (2005)