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Astron. Astrophys. 322, 218-228 (1997)

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Computation of the distance moduli of RR Lyrae stars from their light and colour curves

G. Kovács and J. Jurcsik

Konkoly Observatory, P.O.  Box  67, H-1525 Budapest, Hungary (kovacs@buda.konkoly.hu and jurcsik@buda.konkoly.hu)

Received 5 July 1996 / Accepted 20 November 1996

Abstract

We use B and V data of globular cluster variables to derive a formula for the distance moduli of RRab stars. The method employs the Fourier decomposition of the V light curve and the average [FORMULA] colour index. By using our former result for the [FORMULA] absolute magnitude, we also obtain an expression for the dereddened colour index. With the aid of the new formulae, the relative distance moduli can be estimated within an error of [FORMULA] mag. Although we also make an absolute calibration, it is cautioned that this may be more affected by possible systematic errors originating mostly from the Baade-Wesselink magnitudes. On the basis of the scatter of the individual distance moduli computed with and without reddening correction, it is shown that inhomogeneous reddening plays a role in several clusters. By using our formulae we derive new expressions for the [FORMULA] and K absolute magnitudes on a sample of stars which contains mostly field stars with accurate photometry. As a by-product of this derivation we also give optimum estimations for the selective absorption coefficient [FORMULA]. We show that the K absolute magnitude contains important contribution also from the Fourier parameters, besides the well known dependence on the period. The [FORMULA] absolute magnitude is superbly correlated with the Fourier parameters, which implies that this colour is a very good candidate for the accurate estimation of the absolute magnitude.

Key words: stars: variables – stars: distances – stars: oscillations – stars: horizontal-branch – globular clusters: general

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© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998
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