*Astron. Astrophys. 322, 218-228 (1997)*
## 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 colour index. By using our former result
for the 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 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
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 . We show that
the *K* absolute magnitude contains important contribution also
from the Fourier parameters, besides the well known dependence on the
period. The 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
SIMBAD Objects
### Contents
© European Southern Observatory (ESO) 1997
Online publication: June 30, 1998
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