SIMBAD references

The relation of Kovacs & Walker giving M_v for type ab RR Lyrae stars in terms of their period and Fourier coefficients is calibrated using the new HST parallax of RR Lyrae itself (Benedict et al.). The M_v from this calibrated relation are found for a sample of nearby stars using data given by Jurcsik & Kovacs. These M_v agree well with those obtained from a linear relation in Fe/H by Cacciari, using data from Layden et al. A similar comparison is made for a third simpler empirical relation for M_v that only involves the period of the star.