arXiv subjects

F. Caputo

Publications and source records attributed to F. Caputo.

75 records · Page 5Linked to original sources

arXiv1995

The Topology of RR Lyrae Instability Strip and the Oosterhoff Dichotomy

Convective pulsating models with Y=0.24, stellar mass M=0.65Mo, 0.75Mo, under selected assumptions about luminosities and effective temperatures, are used together with stellar atmosphere computations to get the predicted dependence of RR Lyrae instability strip on stellar mass in the observative plane MV, B-V. The comparison with observed variables belonging to the globular clusters M3 and M15 is presented. It appears that in M3 (Oosterhoff type I) the transition between ab-type and c-type RR Lyrae takes place along the fundamental blue edge, whereas in M15 (Oosterhoff type II) it occurs near the first overtone red edge. This result supports the key role of the hysteresis mechanism originally proposed by van Albada & Baker for explaining the Oosterhoff dichotomy.

astro-ph↗

arXiv1995

RR LYRAE VARIABLE STARS: PULSATIONAL CONSTRAINTS RELEVANT TO THE OOSTERHOFF CONTROVERSY

A solution to the old Oosterhoff controversy is proposed on the basis of a new theoretical pulsational scenario concerning RR Lyrae cluster variables (Bono and coworkers). We show that the observed constancy of the lowest pulsation period in both Oosterhoff type I (OoI) and Oosterhoff type II (OoII) prototypes (M3, M15) can be easily reproduced only by assuming the canonical evolutionary horizontal-branch luminosity levels of these Galactic globular clusters and therefore by rejecting the Sandage period shift effect (SPSE).

astro-ph↗

arXiv1994

HB Morphology and Age Indicators for Metal-Poor Stellar Systems with Age in the Range of 1 to 20 Gyr

Isochrone computations and horizontal branch (HB) models for Y(MS)=0.23 and two values of Z (0.0001, 0.0004)are used to derive constraints on the age indicators and HB morphology of metal-poor clusters with age t (in Gyrs) in the range of 1< t < 20.It is found that for fixed metallicity the luminosity L(3.83) of the zero age horizontalbranch (ZAHB) at the RR Lyrae gap depends on age and that the difference in visual magnitude between main sequence turn-off (TO) and ZAHB may be calibrated in terms of age and metallicity. The results of synthetic HB computations show that at fixed metallicity the mean luminosity of RR Lyraes depends on HB morphology, as well as that the mean luminosity of purely red horizontal branches depends on the age and amount of mass loss during the red giant phase. Such features should be properly taken into account when the cluster age is derived from the observed difference in magnitude between main sequence TO and actual horizontal branch (rather than ZAHB). Moreover, it is shown that the observed HB morphology provides us with an easy estimate of the upper limit of the cluster age. Some useful constraints to the cluster metallicity could be also derived.

astro-ph↗