  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.

Astrophysics