Empirical relations for cluster RR Lyrae stars revisited

¹ Konkoly Observatory, PO Box 67, 1525 Budapest, Hungary
² Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory (The National Optical Astronomy Observatory is operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Fundation.) , Casilla 603, Chile e-mail: awalker@noao.edu

Corresponding author: G. Kovács, kovacs@konkoly.hu

Received: 2 January 2001
Accepted: 28 February 2001

Abstract

Our former study on the empirical relations between the Fourier parameters of the light curves of the fundamental mode RR Lyrae stars and their basic stellar parameters has been extended to considerably larger data sets. The most significant contribution to the absolute magnitude M_V comes from the period P and from the first Fourier amplitude A₁, but there are statistically significant contributions also from additional higher order components, most importantly from A₃ and in a lesser degree from the Fourier phase . When different colors are combined in reddening-free quantities, we obtain basically period-luminosity-color relations. Due to the relation from stellar atmosphere models, we would expect some dependence also on . Unfortunately, the data are still not extensive and accurate enough to decipher clearly the small effect of this Fourier phase. However, with the aid of more accurate multicolor data on field variables, we show that this Fourier phase should be present either in or in or in both. From the standard deviations of the various regressions, an upper limit can be obtained on the overall inhomogeneity of the reddening in the individual clusters. This yields mag, which also implies an average minimum observational error of mag.