Astronomy and Astrophysics – Astronomy
Scientific paper
Jul 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993aj....106..175c&link_type=abstract
Astronomical Journal (ISSN 0004-6256), vol. 106, no. 1, p. 175-180.
Astronomy and Astrophysics
Astronomy
2
Galactic Clusters, Globular Clusters, Horizontal Branch Stars, Lyra Constellation, Stellar Evolution, Milky Way Galaxy, Morphology, Stellar Models
Scientific paper
On the basis of detailed synthetic horizontal-branch (SHB) models, we analyze how different choices of HB evolutionary tracks can affect the predicted period shifts for the RR Lyrae stars in Galactic globular clusters. Previous suggestions that choosing Sweigart's (1987) models leads to a decrease in the predicted period shifts between Oosterhoff type I and II clusters with respect to those obtained through use of the Lee and Demarque (1990) tracks are confirmed and quantified. For OoII clusters with not-too-blue HB morphologies, we find that the increase in predicted period-shift values which results from the inclusion of the final 5-10 percent of HB evolution in the evolutionary tracks is clearly not sufficient to overcome the decrease which results from the adoption of the former tracks instead of the latter. The choice of Sweigart's models leads to a smaller slope for the evolutionary Delta log P(T/eff/)-(Fe/H) relation by about 0.010 if the mean luminosity level of the RR Lyrae variables in the SHB models are employed as a reference for reading the period values, and by about 0.017 if the lower envelopes of the corresponding distributions are used instead - thus further complicating the explanation of the Sandage period-shift effect.
Catelan Márcio
de Freitas Pacheco José Antonio
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