ROTATIONAL MIXING IN EARLY-TYPE STARS - THE MAIN-SEQUENCE EVOLUTION OF A 9-M-CIRCLE-DOT STAR

We describe the main-sequence evolution of a rotating 9 M. star. Its i nterior rotation profile is determined by the redistribution of angula r momentum through the meridian circulation and through the shear turb ulence generated by the differential rotation; the possible effect of internal waves is neglected. We examine the mixing of chemicals produc ed by the same internal motions. Our modelization is based on the set of equations established by Zahn (1992) and completed in Matias, Talon & Zahn (1996). Our calculations show that the amount of mixing associ ated with a typical rotation velocity of similar to 100 km s(-1) yield s stellar models whose global parameters are very similar to those obt ained with the moderate overshooting (d/Hp similar or equal to 0.2) wh ich has been invoked until now to fit the observations. Fast rotation (similar to 300 km s(-1)) leads to significant changes of the C/N and O/N surface ratios, but the abundance of He is barely increased. The m odifications of the internal composition profile due to such rotationa l mixing will certainly affect the post-main-sequence evolution.