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 \pm 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 } ) = ( 0.58–0.68 ) ^ { +0.28 } _ { -0.31 } at [ Fe/H ] =–1.6 .
Furthermore , allowing full use of low accuracy and negative parallaxes as well for 125 RR Lyraes with – 2.49 \leq [ Fe/H ] \leq 0.07 , the maximum likelihood estimation yields the relation , M _ { V } ( { RR } ) = ( 0.59 \pm 0.37 ) + ( 0.20 \pm 0.63 ) ( [ Fe/H ] +1.60 ) , which formally agrees with the recent preferred relation .
The same estimation yields again < M _ { V } ( { RR } ) > = 0.65 \pm 0.33 for the 99 halo RR Lyraes .
Although the formal errors in the latter three parallax estimates are rather large , all of the four results suggest the fainter absolute magnitude , M _ { V } ( { RR } ) \approx 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 flat , matter-dominated universe and current estimates of the Hubble constant .