Astronomy and Astrophysics – Astrophysics
Scientific paper
1997-08-18
Astronomy and Astrophysics
Astrophysics
25 pages, includes 16 figures. To appear in the proceedings of "The Third Conference on Faint Blue Stars," edited by A. G. D.
Scientific paper
The observed abundance variations in globular cluster red giants indicate that these stars may be mixing helium from the hydrogen shell outward into the envelope, presumably as a result of internal rotation. We have investigated the implications of such helium mixing for both the red- giant-branch (RGB) and horizontal-branch (HB) phases by computing a number of noncanonical evolutionary sequences for different assumed mixing depths and mass loss rates. We find that the helium-mixed models evolve to higher luminosities during the RGB phase and consequently lose more mass than their canonical counterparts. This enhanced mass loss together with the higher envelope helium abundances of the helium-mixed models produces a markedly bluer and somewhat brighter HB morphology. As a result, helium mixing can mimic age as a 2nd parameter and can reduce the ages of the metal-poor globular clusters derived from the luminosity difference between the HB and the main-sequence turnoff. Helium mixing might also lead to a larger RR Lyrae period shift and to a steeper slope for the RR Lyrae luminosity - metallicity relation if the mixing is more extensive at low metallicities, as suggested by the observed abundance variations. We discuss the implications of helium mixing for a number of other topics including the low gravities of the blue HB stars, the origin of the extreme HB stars, and the evolutionary status of the sdO stars. A variety of observational tests are presented to test this helium-mixing scenario.
No associations
LandOfFree
Helium Mixing in Globular Cluster Stars does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Helium Mixing in Globular Cluster Stars, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Helium Mixing in Globular Cluster Stars will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-294273