SIMBAD references

We present a theoretical investigation on periods and amplitudes of RR Lyrae pulsators by adopting stellar parameters which cover the range of theoretical evolutionary expectations. Extensive grids of nonlinear, nonlocal and time-dependent convective RR Lyrae envelope models have been computed to investigate the pulsational behavior in both fundamental and first overtone modes at selected luminosity levels and over an effective temperature range which covers the whole instability region. In order to avoid spurious evaluations of modal stability and pulsation amplitudes, the coupling between pulsation and convection was followed through a direct time integration of the leading equations until radial motions approached their limiting amplitude. Blue and red boundaries for pulsational instability into the HR diagram are presented for three different mass values M=0.75, 0.65 and 0.58M_☉, together with an atlas of full amplitude theoretical light curves for both fundamental and first overtone pulsators and for two different assumptions of stellar masses: M=0.75 and 0.65M_☉. The dependence of periods on stellar parameters is discussed and new analytical relations connecting the period to the masses, luminosities and effective temperatures are provided. We show that theoretical expectations concerning minimum fundamental periods are in good agreement with the observational evidence of a dichotomic period distribution between different Oosterhoff type clusters. A rather good correlation has been found between the pulsational amplitude of fundamental pulsators and the effective temperature, rather independently of stellar mass and luminosity. Theoretical periods have been combined with theoretical amplitudes in order to predict the location of the pulsators in the Bailey amplitude-period diagram. Comparison with observational data brings to light what we regard as a clear indication that the OR region, i.e. the region where both fundamental and first overtone show a stable limit cycle, is populated by fundamental or first overtone pulsators in Oosterhoff I and Oosterhoff II clusters respectively. Some evident mismatches between theory and observation have also been found, and they are presented and discussed.