Critically Rotating Post-Main Sequence Stars Hosting a Viscous Decretion Disk

GRANADA, A.; SIGUT, A.; JONES, C.; GEORGY, C.; EKSTROM, S.; MEYNET, G.

Praga

Workshop; The B[e] Phenomenon: Forty Years of Studies; 2016

Stellar evolution calculations of isolated, rotating, intermediate massstars predict that only a handful of these objects reach the criticallimit after the main sequence phase, during the helium burning phase,while describing a blue-loop in the HR diagram. During the redsupergiant stage, angular momentum could be dredged-up to the surface sothat when the star contracts describing the blue-loop, the surfacevelocities can reach larger values than those the star had when crossingthe Hertzprung-Russell diagram for the first time. Even though thesestars might indeed be rare objects, we explore the possibility of suchstars undergoing mechanical mass loss and hence forming a viscousdecretion disk. By taking into account the angular momentum loss ratefrom Geneva stellar evolution calculations for a star with 9 solarmasses and large rotational rate at the ZAMS(Ω/Ωcrit=0.9), combined with the relationsavailable in the literature we obtain the disk outer radius and diskmass loss rate for such an object. Using BEDISK/BERAY codes, wecalculate observables (Hα and other hydrogen lines, forbiddenlines, colors) generated in the gaseous component of the resulting starplus disk system and compare them with observations of evolved starsexhibiting the B[e] phenomenon.