The Relation Between Fourier Coefficients and RR Lyrae Magnitudes

The relation between the Fourier coefficients determined by the light curves of RR Lyrae variables in the Sculptor dwarf galaxy, the M5 cluster, and the unique globular cluster omega-Centauri is investigated. A couple of recent papers claim that it is possible to determine both metallicity and absolute magnitude of RR Lyrae stars from their period and two of the Fourier coefficients. However, this investigation show that fitting high order Fourier series to noisy and/or sparse data results in a large scatter in the determination of the absolute magnitudes. Unless we can find a reasonable way of smoothing noisy data, it will be difficult to use RR Lyrae's as standard candles.