Two double-mode RR Lyrae stars in the field

Abstract

In order to use RR Lyrae stars as reliable distance indicators, it is necessary to know how the masses of these stars are related to the metal abundance. RR Lyrae stars in the field have a greater range of periods and metal abundance than those in globular clusters. Thus, it is important to identifying double-mode RR Lyrae stars (RRd stars) in the field to test the mass-metal abundance relation. Up to the present, however, the only RRd star to have been identified in the field is AQ Leo. Here, evidence is presented for the existence of two others. Data are given on their periods, mean B magnitudes, mode amplitudes, mean B-V colors, masses, and (Fe/H) values. The results give no evidence for a mass-metallicity relationship among the three known RRd field stars, but they show overall agreement with the mass-metallicity relation given by cluster RRd stars. 34 refs.