The Absolute Magnitude Of RR Lyrae Stars

Extract

The present determination of the absolute magnitude .M_v(RR) of RR Lyrae stars is twofold, relying upon Hipparcos proper motions and trigonometric 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 Lyraes with <[Fe/H]> = -1.58. Second, applying the Lutz-Kelker correction to the RR Lyrae HIP95497 with the most accurately measured parallax, we obtain M_v(RR) = 0.57-0.74 at [Fe/H]=-1.6. Furthermore, allowing full use of low accuracy and negative parallaxes as well for 125 RR Lyraes with - 2.49≤[Fe/H]≤0.07, the maximum likelihood estimation 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 yields again My (RR) = 0.65 ± 0.33 for the 99 halo RR Lyraes. Although the formal errors in the latter two estimates are rather large, all of the four results suggest the fainter absolute magnitude, My(RR)=0.6-0.7 at [Fe/H]=-1.6. The present results still provide the lower limit on the age of the universe which is inconsistent with a fiat, matter-dominated universe and current estimates of the Hubble constant.