We show that a straightforward application of the predicted relation connecting the absolute K magnitude of fundamental RR Lyrae variables to their period and metal content , together with current evolutionary predictions on the mass and luminosity of Horizontal Branch stars , supply a distance estimate to the prototype star RR Lyr in close agreement with the recent parallax determination by HST ( Benedict et al .
2002 ) , largely unaffected by the interstellar extinction correction .
Adopting < A _ { V } > =0.12 \pm 0.10 mag as a safe estimate of the extinction correction to RR Lyr , we obtain a ” pulsation ” parallax \pi _ { puls } =3.858 \pm 0.131 mas which agrees quite well , and with a smaller formal error , with the HST measurement ( \pi _ { abs } =3.82 \pm 0.20 mas ) and with the weighted average of HST , Hipparcos , and ground-based determinations ( < \pi _ { abs } > =3.87 \pm 0.19 mas ) .
This result suggests that near-infrared magnitudes and pulsation models could constrain the distance to well-studied RR Lyrae stars , both in the field and in globular clusters , with an accuracy better than current direct trigonometric measurements .