M. Catelan et Jad. Pacheco, ANALYSIS OF EVOLUTIONARY PERIOD-SHIFT PREDICTIONS FOR RR LYRAE STARS IN GALACTIC GLOBULAR-CLUSTERS, The Astronomical journal, 106(1), 1993, pp. 175-180
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 c
lusters. Previous suggestions that choosing Sweigart's [ApJS, 65, 95 (
1987)] models leads to a decrease in the predicted period shifts betwe
en Oosterhoff type I and II clusters with respect to those obtained th
rough use of the Lee & Demarque [ApJS, 73, 709 (1990)] tracks are conf
irmed and quantified. For OoII clusters with not-too-blue HB morpholog
ies (i.e., M15-like), we find that the increase in predicted period-sh
ift values which results from the inclusion of the final 5%-10% of HB
evolution in the evolutionary tracks is clearly not sufficient to over
come the decrease which results from the adoption of the former tracks
instead of the latter. The choice of Sweigart's models leads to a sma
ller slope for the evolutionary DELTA log P(T(eff)-[Fe/H] relation by
congruent-to 0.010 if the mean luminosity level of the RR Lyrae variab
les in the SHB models are employed as a reference for reading the peri
od values, and by congruent-to 0.017 if the lower envelopes of the cor
responding distributions are used instead-thus further complicating th
e explanation of the Sandage period-shift effect.