Eleven double-mode (dm) RR Lyrae stars, with periods midway between the periods for the c-type and ab-type RR Lyrae stars, have been identified in the Draco dwarf galaxy by reanalyzing the photometry of Baade and Swope (1961) for 35 stars. In the Ursa Minor dwarf galaxy, five probable dm RR Lyrae stars have been identified from among the stars measured by van Agt (1967, 1968). A dm RR Lyrae star also has been discovered in the LMC globular cluster NGC 2257 (Nemec, 1983; Nemec, Liller and Hesser 1984). Preliminary analysis of the Martin (1938) photometry for 54 stars in the Galactic globular cluster ω Centauri (Nemec and Norris 1983) shows no evidence for double-mode RR Lyrae stars.
Observational Tests of the Stellar Evolution Theory
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