Evolution of Galactic Field be Stars

Galactic field Be stars were studied by taking into account the effects induced by the fast rotation on their fundamental parameters. Fractional ages $\tau/\tau\_{\rm MS}$ ($\tau\_{\rm MS}$ = time spent in the MS) against stellar mass reveal that: a) Be stars spread over the whole interval $0<\tau/\tau\_{\rm MS}<1$; 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.