Coupled mass and angular momentum loss of massive main sequence stars

We investigate the interaction of mass loss and rotation during core hydrogen burning in massive stars. We compute their main sequence evolution assuming rigid rotation, and carry angular momentum as a passive quantity in the stellar interior but incorporate its effect on the stellar mass loss rate. We consider the example of a 60M_sun star assuming various initial rotation rates. We show that rotation may substantially enhance the total main sequence mass loss of massive stars. Furthermore, we argue that the surface layers of rotating massive main sequence stars may reach the limit of hydrostatic stability (``Omega -limit'') by achieving a considerable fraction of their Eddington luminosity. We show that this process is not catastrophic for the star, but rather that the coupling of mass and angular momentum loss limits the mass loss rate dot M_Ω of main sequence stars at the Omega -limit. dot M_Ω is determined through the angular momentum loss imposed by the Omega -limit rather than by atomic physics. For our 60M_sun sequences, it is dot M_Ω =~ 10(-5) M_sun yr(-1) . We find a convergence of the rotational velocities of main sequence stars of a given initial mass at the Omega -limit, but a strong dependance of their mass at core hydrogen exhaustion from the initial rotation rate. Since then also the post-main sequence evolution depends on the initial amount of angular momentum, we argue that this is a third independent initial parameter for the evolution of massive stars, as important as initial mass and metallicity. We briefly discuss observable consequences of the coupling of mass and angular momentum loss, e.g. a significant decline of the projected rotational velocity v sin i towards the cool end of the main sequence, a period of strongly enhanced and aspherical mass loss, disks or rings in the equatorial plane of the star reminiscent of B[e]-stars, and highly bipolar circumstellar structures.