Metallicity of clusters from RRab pulsators: results of an automatic analysis

Abstract

We apply the photometric method of Jurcsik &38; Kovacs to newly available observations of RRab pulsators in clusters, in order to determine such physical properties as metallicity [Fe/H] and absolute magnitudes MV. For this purpose we devised a fully automatic algorithm for reliable and repeatable determination of Fourier parameters from light curves without resorting to smoothing and/or interpolation, employed in the past. In this way we demonstrate that these parameters form solid foundations for the method of Jurcsik &38; Kovacs. Whether these parameters lead to reliable determination of [Fe/H] and MV for RRab stars, as postulated by Jurcsik &38; Kovacs, still remains an open question. Our photometric average cluster metallicities 〈[Fe/H]〉phot for M3, M5, M68, ω Cen and NGC 288 correlate reasonably well with their spectroscopic determinations 〈[Fe/H]〉sp, supporting Jurcsik &38; Kovacs. However, for individual RRab stars in ω Cen we were not able to reproduce expected correlations between 〈V〉 (i.e. MV), 〈[Fe/H]〉phot and 〈[Fe/H]〉sp. As chemical composition in ω Cen is known to vary, the existence of such correlations is expected.