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[55.04] Onset of mass loss in red giants: association with an evolutionary event

D.J. Mullan (Bartol Research Institute), J. MacDonald (University of Delaware)

Stencel and Mullan (1980) used asymmetries in the MgII k emission line profile to determine the location of a ``velocity dividing line" (VDL) in the H-R diagram. Stars to the right of (and above) the VDL were observed to have asymmetries which are consistent with the presence of cool massive winds. Stars to the left of (and below) the VDL showed no evidence for winds. We show that the VDL lies close to a certain event of stellar evolution on the red giant branch (RGB). The event occurs when the hydrogen-burning shell evolves outward through a discontinuity in molecular weight. In some low-mass stars, this event causes a kink in the evolutionary track of an individual low mass star. In a cluster, the combined effects of such kinks create a ``bump" in the luminosity function. We conclude that evolution through the kink (or bump) on the RGB is associated with the onset of a cool massive wind. We speculate that this evolutionary event is associated with a change in dynamo mode.

Work supported by NASA DE Space Grant.

The author(s) of this abstract have provided an email address for comments about the abstract: mullan@bartol.udel.edu

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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.