497 research outputs found
CCD PHOTOMETRY OF RR LYRAE STARS IN M5 AS A TEST FOR THE PULSATIONAL SCENARIO
In this paper we present new CCD investigations of RR Lyrae pulsators in the
Oo.I globular cluster M5. B V curves of light for 15 RR Lyrae are presented.
With the addition of further 11 curves of light by Storm, Carney and Beck
(1991) one is dealing with a sample of 26 well studied cluster pulsators whose
properties have been implemented with similar data for RR Lyrae in clusters M3,
M15, M68 to allow a comparison with the theoretical scenario recently presented
by Bono and Stellingwerf (1994). On this basis, we discuss the distribution of
stars in the period amplitude diagram, disclosing a substantial reduction of
Sandage's period shift. We suggest that theoretical constraints concerning
periods and amplitudes could allow information on masses and luminosity of the
pulsators directly from Bailey's diagram only. Static temperatures have been
derived for all stars in the sample, discussing the dependence on the
temperature of the observed pulsational properties.Comment: postscript file of 17 pages of text plus 7 figures and 2 tables. For
any problem please write to [email protected]
Pulsational M_V versus [Fe/H] relation(s) for globular cluster RR Lyrae variables
We use the results from recent computations of updated non-linear convective
pulsating models to constrain the distance modulus of Galactic globular
clusters through the observed periods of first overtone RRc pulsators. The
resulting relation between the mean absolute magnitude of RR Lyrae stars
and the heavy element content [Fe/H] appears well in the range of
several previous empirical calibrations, but with a non linear dependence on
[Fe/H] so that the slope of the relation increases when moving towards larger
metallicities. On this ground, our results suggest that metal-poor
([Fe/H]-1.5) variables follow two different
linear -[Fe/H] relations. Application to RR Lyrae stars in the
metal-poor globular clusters of the Large Magellanic Cloud provides a LMC
distance modulus of the order of 18.6 mag, thus supporting the "long" distance
scale. The comparison with recent predictions based on updated stellar
evolution theory is shortly presented and discussed.Comment: 8 pages, 4 postscript figures, accepted for publication on MNRA
A theoretical approach for the interpretation of pulsating PMS intermediate-mass stars
The investigation of the pulsation properties of pre-main-sequence
intermediate-mass stars is a promising tool to evaluate the intrinsic
properties of these stars and to constrain current evolutionary models. Many
new candidates of this class have been discovered during the last decade and
very accurate data are expected from space observations obtained for example
with the CoRoT satellite. In this context we aim at developing a theoretical
approach for the interpretation of observed frequencies, both from the already
available ground-based observations and from the future more accurate and
extensive CoRoT results. To this purpose we have started a project devoted to
the computations of fine and extensive grids of asteroseismic models of
intermediate mass pre-main-sequence stars. The obtained frequencies are used to
derive an analytical relation between the large frequency separation and the
stellar luminosity and effective temperature and to develop a tool to compare
theory and observations in the echelle diagram. The predictive capabilities of
the proposed method are verified through the application to two test stars. As
a second step, we apply the procedure to two true observations from multisite
campaigns and we are able to constrain their stellar parameters, in particular
the mass, in spite of the small number of frequencies. We expect that with a
significantly higher number of frequencies both the stellar mass and age could
be constrained and, at the same time, the physics of the models could be
tested.Comment: Accepted for publication on A&
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