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On the explanation of the Sandage effect

Published online by Cambridge University Press:  15 February 2018

M. Catelan
M. Catelan*
Affiliation:
Instituto Astronômico e Geofísico, Universidade de São Paulo, São Paulo, Brazil

Extract

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There are two problems with the Lee et al. (1990, LDZ; Lee 1990, 1991) scenario for the Sandage effect (Sandage 1990 and references therein) which may still warrant further detailed analyses: 1) on the basis of standard tracks, RR Lyrae stars in OoII, M15-like globular clusters can only be well-evolved objects from the blue ZAHB for unrealistically low helium abundance (Y) values; 2) in comparison with the models by Sweigart (1987, SW87), the evolutionary tracks of Lee & Demarque (1990, employed by LDZ) tend to overestimate the effect of evolution away from the ZAHB for the RR Lyrae stars, despite the similar assumptions involved in the calculations of the two sets of models. (See Catelan 1992a, C92A.)

Type
Theoretical Breakthroughs
Information
International Astronomical Union Colloquium , Volume 139: New Perspectives on Stellar Pulsation and Pulsating Variable Stars , 1993 , pp. 280
Copyright
Copyright © Cambridge University Press 1993

References

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