Modeling of RR Lyrae light curves: the case of M3

Context: A promising technique to derive the physical parameters and the distance of pulsating stars is the fit of the observed light curves by nonlinear pulsation models.
Aims: We apply this technique to a subsample of the RR Lyrae belonging to the Galactic globular cluster M3. The application of the method to cluster pulsators has the advantage of dealing with a homogeneous sample at the same distance and with the same chemical composition allowing to be checked the internal consistency of pulsational calculations.
Methods: We selected seven pulsators (three RRc and four RRab) which cover a significant period range and show detailed light curves in the B, V and in some cases I bands. For four of them, with different periods, pulsation modes and light curve properties, we analyze the dependence of the theoretical light curve variations on the model input parameters.
Results: For all selected objects, except the reddest one, we are able to theoretically reproduce the observed light curve morphology for self-consistent ranges of intrinsic stellar parameters, in agreement with the evolutionary predictions for the corresponding metal abundance. It is worth noting that, even if the theoretical reproduction of individual light curves gives for each variable only a range of stellar parameters and distances, the analysis of several variables belonging to the same cluster provides a mean distance modulus, namely μ_V=15.10 ± 0.1 mag, and also checks the self-consistency of the adopted theoretical scenario. Taking also into account the evolutionary constraints, the range of the accepted distance modulus is significantly reduced giving a weighted mean value of 15.05 ± 0.02. Our estimates are in agreement with available results in the literature obtained from independent methods.

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