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The effect of Livermore OPAL opacities on the evolutionary masses of RR Lyrae starsWe have investigated the effect of the new Livermore OPAL opacities on the evolution of horizontal-branch (HB) stars. This work was motivated by the recent stellar pulsation calculations using the new Livermore opacities, which suggest that the masses of double-mode RR Lyrae stars are 0.1-0.2 solar mass larger than those based on earlier opacities. Unlike the pulsation calculations, we find that the effect of opacity change on the evolution of HB stars is not significant. In particular, the effect of the mean masses of RR Lyrae stars is very small, showing a decrease of only 0.01-0.02 solar mass compared to the models based on old Cox-Stewart opacities. Consequently, with the new Livermore OPAL opacities, both the stellar pulsation and evolution models now predict approximately the same masses for the RR Lyrae stars. Our evolutionary models suggest that the mean masses of the RR Lyrae stars are about 0.76 and about 0.71 solar mass for M15 (Oosterhoff group II) and M3 (group I), respectively. If (alpha/Fe) = 0.4, these values are decreased by about 0.03 solar mass. Variations of the mean masses of RR Lyrae stars with HB morphology and metallicity are also presented.
Document ID
19930061222
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Yi, Sukyoung
(NASA Headquarters Washington, DC United States)
Lee, Young-Wook
(NASA Headquarters Washington, DC United States)
Demarque, Pierre
(Yale Univ. New Haven, CT, United States)
Date Acquired
August 16, 2013
Publication Date
July 1, 1993
Publication Information
Publication: Astrophysical Journal, Part 2 - Letters
Volume: 411
Issue: 1
ISSN: 0004-637X
Subject Category
Astrophysics
Accession Number
93A45219
Funding Number(s)
CONTRACT_GRANT: NAGW-2531
Distribution Limits
Public
Copyright
Other

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