New Calibrations of Pulsational Absolute Magnitudes of Field RR Lyrae   Stars Using Revised Dependencies of Temperatures, Masses, and Periods on   Metallicity
  The pulsational method to estimate the absolute magnitudes of RR Lyrae stars is updated with new data on field-star metallicities by Layden, a new calibration of the (B-V)_0-temperature correlation from recent atmospheric models by Bell and Tripicco, and new mass estimates by Bono et al. New linear and non-linear calibrations of M_V(RR)=f([Fe/H]) are derived that depend on the nature of the adopted envelope in a diagram of log period versus metallicity fitted to the shortest period field variables in each metallicity range, together with the stated assumptions on the colour of the stars at that envelope. These new cali- brations are compared with a recent non-linear calibration by Caputo et al. The theoretical luminosity zero points for each of the three new calibrations derived here agree with each other to within 0.1 mag over the metallicity range of -1.0>[Fe/H]>-2.0. Comparison with the empirical absolute magnitude calibra- tion of M_V(RR)=+0.52 at [Fe/H]=-1.5 by Clementini at al. from RR Lyraes in LMC also shows agreement at the 0.05 mag level at the stated metallicity. Our final compromise pulsational calibration is, M_V(RR)=0.82 + 0.20([Fe/H]) with the caveat that the true relation is likely to be non-linear at the 0.1 mag level for [Fe/H] values between -0.5 and -2.0, hence with variable dM_V/d([Fe/H]) slopes that cover the range from 0 to 0.6 for different metallicities. (...) 
Allan Sandage (Carnegie Observatories, Pasadena, CA)