Astron. Astrophys. 348, L33-L36 (1999) Letter to the Editor The absolute magnitudes of RR Lyrae stars from HIPPARCOS parallaxes ^{*}
M.A.T. Groenewegen^{ 1} and
M. Salaris^{ 2,1}
Received 7 June 1999 / Accepted 13 July 1999 Abstract Using the method of "reduced parallaxes" for the Halo RR Lyrae stars in the HIPPARCOS catalogue we derive a zero point of 0.77 0.26 mag for an assumed slope of 0.18 in the -[Fe/H] relation. This is 0.28 magnitude brighter than the value Fernley et al. (1998a) derived by employing the method of statistical parallax for the identical sample and using the same slope. We point out that a similar difference exists between the "reduced parallaxes" method and the statistical parallax method for the Cepheids in the HIPPARCOS catalogue. We also determine the zero point for the - relation, and obtain a value of -1.16 0.27 mag (for a slope of -2.33). The distance moduli to the HIPPARCOS RR Lyrae stars derived from the two relations agree well. The derived distance scale is in good agreement with the results from the Main Sequence fitting distances of Galactic globular clusters and with the results of theoretical Horizontal Branch models, and implies a distance modulus to the LMC of 18.61 0.28 mag. Key words: stars: variables: RR Lyr stars: distances galaxies: Magellanic Clouds
* Based on data from the ESA Hipparcos astrometry satellite. Send offprint requests to: Martin Groenewegen (groen@mpa-garching.mpg.de) Contents© European Southern Observatory (ESO) 1999 Online publication: July 26, 1999 |