Fundamental physical parameters of RRab stars
Received 20 May 1997 / Accepted 14 January 1998
The intrinsic mean colours and the metallicity of RRab stars calculated from the light curve parameters are shown to be consistent with the Kurucz model atmosphere results if the zero points of the and colours are corrected. This consistency justifies the application of bolometric correction and temperature transformations derived from the Kurucz models in determining the corresponding static values of the luminosity and effective temperature of the variables. Since we can also infer the mass by using the fundamental pulsation equation, all the basic physical parameters of any variable with known light curve can be determined. The accuracy of the calculated , , and [Fe/H] values are estimated to be 0.009, 0.003, 0.026 and 0.14 dex, respectively.
The method enables us to derive the above parameters for a large sample of RRab stars, thus the basic relations among the physical parameters can also be given. Although the zero points of the physical parameters are somewhat ambiguous, the slopes of these relations are quite precise. The comparison with pulsational and evolutionary model predictions leads to the following conclusions: (a) there is no pulsational model calculation which explains the strong dependence of the temperature on the luminosity although this is one of the most significant relations defined by the empirical data; (b) the slopes of the different relations between the fundamental physical parameters agree with the results of horizontal branch models well; (c) determining the metallicity dependence of , and , the various contributions which induce the observed shift of the average periods of RR Lyrae stars with metallicity (Sandage period-shift), can be correctly separated; (d) the data show that the more evolved, post zero-age horizontal branch objects are typically found amongst the most metal-poor variables.
Key words: stars: fundamental parameters stars: horizontal-branch stars: RR Lyrae
© European Southern Observatory (ESO) 1998
Online publication: April 20, 1998