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Astron. Astrophys. 330, 515-520 (1998)

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The absolute magnitudes of RR Lyraes from HIPPARCOS parallaxes and proper motions *

J. Fernley 1, T.G. Barnes 2, I. Skillen 1, S.L. Hawley 3, C.J. Hanley 3, D.W. Evans 4, E. Solano 1 and R. Garrido 5

1 IUE Observatory, P.O. Box 50727, E-28080 Madrid, Spain (jaf or wji or esm@vilspa.esa.es)
2 McDonald Observatory, University of Texas, Austin, Texas 78712, USA (tgb@astro.as.utexas.edu)
3 Department Physics and Astronomy, Michigan State University, E. Lansing, Michigan 48824, USA (slh or chris@pillan.pa.msu.edu)
4 Royal Greenwich Observatory, Madingley Rd, Cambridge CB3 OHA, England (dwe@ast.cam.ac.uk)
5 Inst. Astrofisica de Andalucia, Apdo 3004, E-18080 Granada, Spain (garrido@iaa.es)

Received 18 June 1997 / Accepted 27 August 1997

Abstract

We have used HIPPARCOS proper motions and the method of Statistical Parallax to estimate the absolute magnitude of RR Lyrae stars. In addition we used the HIPPARCOS parallax of RR Lyrae itself to determine it's absolute magnitude. These two results are in excellent agreement with each other and give a zero-point for the RR Lyrae [FORMULA],[Fe/H] relation of 0.77 [FORMULA] 0.15 at [Fe/H]=-1.53. This zero-point is in good agreement with that obtained recently by several groups using Baade-Wesselink methods which, averaged over the results from the different groups, gives [FORMULA] = 0.73 [FORMULA] 0.14 at [Fe/H]=-1.53. Taking the HIPPARCOS based zero-point and a value of 0.18 [FORMULA] 0.03 for the slope of the [FORMULA],[Fe/H] relation from the literature we find firstly, the distance modulus of the LMC is 18.26 [FORMULA] 0.15 and secondly, the mean age of the Globular Clusters is 17.4 [FORMULA] 3.0 GYrs. These values are compared with recent estimates based on other "standard candles" that have also been calibrated with HIPPARCOS data. It is clear that, in addition to astrophysical problems, there are also problems in the application of HIPPARCOS data that are not yet fully understood.

Key words: stars: variables: RR Lyraes – Galaxy: Globular Clusters – galaxies: Magellanic Clouds

* Table 1, which contains the basic data for the RR Lyraes, is available only at CDS. It may be retrieved via anonymous FTP at cdsarc.u-strasbg.fr (130.79.128.5) or via the Web at http://cdsweb.u-strasbg.fr/Abstract.html

Send offprint requests to: J. Fernley

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© European Southern Observatory (ESO) 1998

Online publication: January 16, 1998
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