RR Lyrae pulsational temperature scales: On the consistency between different empirical relations

Abstract

In this paper, by assuming as correct equilibrium temperatures of RRab Lyrae variables those defined from Carney, Storm & Jones (1992, CSJ), we show that temperatures derived from (B-V) colour (mean colour over the pulsational cycle calculated on the magnitude scale) by Bessel, Castelli & Plez 1998 (BCP) transformations, are consistent with CSJ equilibrium temperatures within a probable error of $\delta \log T_e = \pm 0.003$. As a consequence it is shown that the pulsational temperature scale, temperature-period-blue amplitude ($T_{eff}=f(P,A_B)$), provided by De Santis (1996, DS96) by (B-V) colour of about 70 stars of Lub's sample, is a suitable relation, reddening and metallicity free, to calculate equilibrium temperatures for RRab variables. This relation is independent from variable mass and luminosity within a large range of period-shift from the mean period-amplitude relation valid for the Lub's sample of variables. On the contrary, it is also shown that a temperature-amplitude-metallicity relation is strictly dependent from the period-amplitude relation of the sample used for calibrating it: we prove this means that it is dependent from both mass and luminosity variations of variables.