A&A Supplement series, Vol. 121, February 1977, 327-341
Received February 12; accepted May 9, 1996
G. Bono - F. Caputo
-
V. Castellani
- M. Marconi
Send offprint request: G. Bono
Osservatorio Astronomico di Trieste, Via G.B.Tiepolo 11,
34131 Trieste, Italy
e-mail: bono@oat.ts.astro.it
Istituto di Astrofisica Spaziale, CNR, C.P. 67, 00044 Frascati,
Italy
e-mail: caputo@saturn.ias.fra.cnr.it
Dipartimento di Fisica, Università di Pisa, Piazza Torricelli 2,
56126 Pisa, Italy
e-mail: marcella@astr1pi.difi.unipi.it
Osservatorio Astronomico Collurania, 64100 Teramo, Italy
e-mail: vittorio@astr1pi.difi.unipi.it
Laboratori del Gran Sasso, INFN, 67100 L'Aquila, Italy
We present a theoretical investigation
on periods and amplitudes of RR Lyrae pulsators
by adopting stellar parameters which
cover the range of theoretical evolutionary expectations.
Extensive grids of nonlinear, nonlocal and time-dependent
convective RR Lyrae envelope models have been computed to investigate
the pulsational behavior in both
fundamental and first overtone modes at selected luminosity
levels and over an effective temperature range which covers the
whole instability region. In order to avoid spurious evaluations
of modal stability
and pulsation amplitudes, the coupling between pulsation and
convection was followed through a direct time integration of the
leading equations until radial motions approached their limiting
amplitude.
Blue and red boundaries for pulsational instability into the HR diagram
are presented for three different mass values M=0.75, 0.65 and 0.58
, together with an atlas of full amplitude theoretical
light curves for both fundamental and first overtone pulsators
and for two different assumptions of stellar masses: M=0.75 and 0.65
. The dependence of periods on stellar parameters
is discussed and new analytical relations connecting the period to the
masses, luminosities and effective temperatures are provided.
We show that theoretical expectations concerning
minimum fundamental periods are in good agreement with the
observational evidence of a dichotomic period distribution
between different Oosterhoff type clusters.
A rather good correlation has been found between the pulsational
amplitude of fundamental pulsators and the effective temperature,
rather independently of stellar mass and luminosity.
Theoretical periods have been combined with theoretical amplitudes
in order to
predict the location of the pulsators in the Bailey amplitude-period
diagram. Comparison with observational data brings to light what we regard
as a clear indication that the OR region, i.e. the region where
both fundamental and first overtone show a stable limit cycle,
is populated by fundamental or first overtone pulsators in
Oosterhoff I and Oosterhoff II clusters respectively. Some
evident mismatches between theory and observation have also been found,
and they are presented and discussed.
keywords: stars: variables: other (RR Lyrae) -- stars: oscillations -- stars: horizontal-branch -- globular clusters: individual: M 3, M 5, M 15