The database of intermediate mass rotating stellar models presented in the
past years by the Geneva Stellar Evolution Group can be used to build synthetic
stellar populations that fully account for the effects of stellar rotation.
However, up to now we still lacked stellar evolutionary tracks that rotate
close to the critical limit during the whole MS phase. This occurs because the
flat internal profile of rotation imposed at the Zero-Age MS (ZAMS) is modified
by the action of meridional currents immediately after the ZAMS, causing the
surface rotational velocity to decrease abruptly until it reaches a
quasi-stationary state. We compute stellar models with non-solid rotation at
the ZAMS to obtain stellar evolutionary tracks with a larger content of angular
momentum, that attain rotational equatorial velocities close to the critical
limit throughout their MS phase. These models have a longer MS lifetime and a
higher surface chemical enrichment already at the end of the MS, particularly
at Z=0.002. Stellar models with solid rotation at the ZAMS adequately represent
the overall characteristics and evolution of differentially rotating models of
identical angular momentum content, but with a lower initial surface rotational
velocity. For these models we recommend to use as the initial rotational rate
the values derived once the quasi-stationary state is reached, after the abrupt
decrease in surface velocity. Interestingly, the initial equatorial rotational
velocities are virtually metallicity independent for the stellar models we
computed with the same mass and angular momentum content at the ZAMS. If, as
some observational evidence indicates, B-type stars at Z=0.002 rotate with a
higher equatorial velocity at the ZAMS than stars with Z=0.014, our finding
would indicate that the angular momentum content of B-type stars in the SMC is
higher than their Galactic counterparts.Comment: 15 pages, Accepted for publication in A&
