THE ABSOLUTE MAGNITUDE OF RR LYRAE STARS DERIVED FROM THE HIPPARCOS CATALOG

The present determination of the absolute magnitude M-v(RR) of RR Lyra e stars is twofold, relying upon Hipparcos proper motions and trigonom etric parallaxes separately. First, applying the statistical parallax method to the proper motions, we find [M-v(RR)] = 0.69 +/- 0.10 for 99 halo RR Lyrae stars with [[Fe/H]] = -1.58. Second, applying the Lutz- Kelker correction to the RR Lyrae HIP 95497 with the most accurately m easured parallax, we obtain M-v(RR) = (0.58-0.68)(-0.31)(+0.28) at [Fe /H] = -1.6. Furthermore, allowing full use of low-accuracy and negativ e parallaxes, as well 125 RR Lyrae stars with -2.49 less than or equal to [Fe/H] less than or equal to 0.07, the maximum likelihood estimati on yields the relation M-v(RR) = (0.59 +/- 0.37) + (0.20 +/- 0.63)([Fe /H] + 1.60), which formally agrees with the recent preferred relation. The same estimation again yields [M-v(RR)] = 0.65 +/- 0.33 for the 99 halo RR Lyrae stars. Although the formal errors in the latter three p arallax estimates are rather large, all four results suggest the faint er absolute magnitude, M-v(RR) approximate to 0.6-0.7 at [Fe/H] = -1.6 . The present results still provide the lower limit on the age of the universe that is inconsistent with a flat, matter-dominated universe a nd current estimates of the Hubble constant.