Physical parameters of the Small Magellanic Cloud RR Lyrae stars and the distance scale

Abstract

We present a careful and detailed light curve analysis of RR Lyrae stars in the Small Magellanic Cloud (SMC) discovered by the Optical Gravitational Lensing Experiment (OGLE) project. Out of 536 single mode RR Lyrae stars selected from the database, we have investigated the physical properties of 335 `normal looking' RRab stars and 17 RRc stars that have good quality photometric light curves. We have also been able to estimate the distance modulus of the cloud which is in good agreement with those determined from other independent methods. The Fourier decomposition method has been used to study the basic properties of these variables. Accurate Fourier decomposition parameters of 536 RR Lyrae stars in the OGLE-II database are computed. Empirical relations between the Fourier parameters and some physical parameters of these variables have been used to estimate the physical parameters for the stars from the Fourier analysis. Further, the Fourier decomposition of the light curves of the SMC RR Lyrae stars yields their mean physical parameters as: [Fe/H] = -1.56 $\pm 0.25$, M = 0.55 $\pm $ 0.01 M$_{\odot}$, T$_{\rm eff} = 6404 \pm 12$ K, $\log \rm L = 1.60 \pm0.01 \rm L_\odot$ and M$\rm_V = 0.78 \pm0.02 $ for 335 RRab variables and [Fe/H] = -1.90 $\pm$ 0.13, M = 0.82 $\pm $ 0.18 M$_{\odot}$, T$_{\rm eff} = 7177 \pm 16$ K, $\log \rm L = 1.62 \pm 0.02 \rm L_{\odot}$ and M$\rm_V = 0.76 \pm 0.05$ for 17 RRc stars.