A pulsational approach to the luminosity of horizontal branch stellar structures

We discuss an alternative approach to constrain the absolute bolometric lum inosity of zero-age horizontal branch (ZAHB) structures by using the observ ational pulsational properties of ab-type RR Lyrae stars, theoretical relat ions connecting these properties to the evolutionary ones, i.e. luminosity, mass and effective temperature, and also the location in the Hertzsprung-R ussell diagram of the instability strip boundaries for fundamental pulsator s. As the main goal of this work is to obtain an evaluation of the ZAHB bol ometric luminosity as independent of stellar evolution theory as possible, we have minimized the use of evolutionary prescriptions, the only adopted e volutionary input being the allowed mass range for fundamental pulsators. N evertheless, the effects on our final results related to these evolutionary prescriptions have been carefully checked. In order to test the accuracy of the current framework, we have carefully i nvestigated the effective temperature scale provided by De Santis and adopt ed in the present work. It has been found that the pulsational colour-effec tive temperature scale fixed by this temperature scale and the relation bet ween intrinsic (B-V)(0) colour, blue amplitude and metallicity given by Cap uto & De Santis appear fully consistent with both theoretical colour transf ormations, given by Castelli, Gratton & Kurucz and Buser & Kurucz, and a se mi-empirical one, provided by Green. In contrast, there is a large discrepa ncy between this pulsational colour-temperature scale and the one based on the Kurucz model atmospheres. The effects of adopting the temperature scale of Catelan, Sweigart & Borissova have been investigated. The reliability of the method is shown by applying it to a selected sample of globular clusters (GCs), the heavy element abundances of which cover alm ost all the complete GC metallicity range. In order to verify the accuracy of the results obtained by using ab-type RR Lyrae stars, a similar analysis has also been performed by using both observational and theoretical eviden ce for first-overtone variables. The results obtained for the ZAHB bolometr ic luminosities have been critically analysed and a comparison with recent evolutionary prescriptions has also been performed. The existence of eviden t mismatches between current results and some evolutionary models has been verified and discussed. Finally, our investigation has been extended to field variables to check fo r a luminosity difference between cluster RR Lyrae stars and field ones as suggested by Gratton. The comparison between the pulsational properties of field and cluster variables does not show the existence of any significant difference in their intrinsic luminosity, thus providing further support to the results obtained by Catelan.