$\Omega$-Slow Solutions and Be Star Disks

Abstract

As the disk formation mechanism(s) in Be stars is(are) as yet unknown, we investigate the role of rapidly rotating radiation-driven winds in this process. We implemented the effects of high stellar rotation on m-CAK models accounting for: the shape of the star, the oblate finite disk correction factor, and gravity darkening. For a fast rotating star, we obtain a two-component wind model, i.e., a fast, thin wind in the polar latitudes and an $\Omega$-slow, dense wind in the equatorial regions. We use the equatorial mass densities to explore H$\alpha$ emission profiles for the following scenarios: 1) a spherically symmetric star, 2) an oblate shaped star with constant temperature, and 3) an oblate star with gravity darkening. One result of this work is that we have developed a novel method for solving the gravity darkened, oblated m-CAK equation of motion. Furthermore, from our modeling we find a) the oblate finite disk correction factor, for the scenario considering the gravity darkening, can vary by at least a factor of two between the equatorial and polar directions, influencing the velocity profile and mass-loss rate accordingly, b) the H$\alpha$ profiles predicted by our model are in agreement with those predicted by a standard power-law model for following values of the line-force parameters: $1.5\lesssim k\lesssim 3$, $\alpha \sim 0.6$ and $\delta \gtrsim 0.1$, and c) the contribution of the fast wind component to the H$\alpha$ emission line profile is negligible; therefore, the line profiles arise mainly from the equatorial disks of Be stars.

arXiv comment20 pages and 14 figures. Accepted for publication in The Astrophysical Journal

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• Evolution of massive stars with new hydrodynamic wind models
• Be and Bn stars: Balmer discontinuity and stellar-class relationship
• Radiation-Driven Wind Hydrodynamics of Massive Stars: A Review
• Evolution of rotating massive stars with new hydrodynamic wind models
• New self-consistent wind parameters fitting optical spectra of O-type stars observed with HERMES spectrograph
• Co-existence and switching between fast and $\Omega$-slow wind solutions in rapidly rotating massive stars