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]

RR Lyrae variables in M5 as a test of pulsational theory

We present B and V CCD photometry for variables in the cluster central region, adding new data for 32 variables and giving suitable light curves, mean magnitudes and corrected colors for 17 RR Lyrae. Implementing the data given in this paper with similar data already appeared in the literature we discuss a sample of 42 variables, as given by 22 RRab and 20 RRc, to the light of recent predictions from pulsational theories. We find that the observational evidence concerning M5 pulsators appears in marginal disagreement with predictions concerning the color of the First Overtone Blue Edge (FOBE), whereas a clear disagreement appears between the ZAHB luminosities predicted through evolutionary or pulsational theories.Comment: 7 pages, 7 postscript figures, accepted for publication on MNRA

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

Bright Stars in the Galactic Globular M5

We present a CCD investigation of the galactic globular M5 aimed to increase the statistical relevance of the available sample of evolving bright stars. Previous investigations, limited to the outer cluster region, have been extended toward the cluster center, more than doubling the number of observed luminous stars. On this basis, we discuss a statistically relevant sample, rich of 415 HB stars. The occurrence of a gap in the blue side of the HB is suggested. Comparison to the current evolutionary scenario discloses a good agreement concerning both the C-M diagram location and the relative abundance of stars in the advanced evolutionary phases, supporting our present knowledge of the evolution of low mass stars. Determination of the amount of the original helium content through the ratio R N(HB)/N(RGB) gives $Y = 0.22 \pm 0.02$.Comment: 16 pages, Standard TeX, 4 figures available upon request from [email protected]

Kepler observations of A-F pre-main sequence stars in Upper Scorpius: Discovery of six new δ\delta~Scuti and one γ\gamma~Doradus stars

We present light curves and periodograms for 27 stars in the young Upper Scorpius association (age=$11 \pm 1$\,Myr) obtained with the Kepler spacecraft. This association is only the second stellar grouping to host several pulsating pre-main sequence (PMS) stars which have been observed from space. From an analysis of the periodograms, we identify six $\delta$~Scuti variables and one $\gamma$~Doradus star. These are most likely PMS stars or else very close to the zero-age main sequence. Four of the $\delta$~Scuti variables were observed in short-cadence mode, which allows us to resolve the entire frequency spectrum. For these four stars, we are able to infer some qualitative information concerning their ages. For the remaining two $\delta$~Scuti stars, only long-cadence data are available, which means that some of the frequencies are likely to be aliases. One of the stars appears to be a rotational variable in a hierarchical triple system. This is a particularly important object, as it allows the possibility of an accurate mass determination when radial velocity observations become available. We also report on new high-resolution echelle spectra obtained for some of the stars of our sample.Comment: 19 pages, 9 figures. Accepted for publication on MNRA