A photometric monitoring of bright high-amplitude δ Scuti stars - I. The double-mode pulsation of V567 Ophiuchi

We present the first results of an observational project, which addresses the period changing behaviour of a sample of high-amplitude Scuti stars. In this paper we discuss the double-mode nature of V567 Ophiuchi. It was observed on 15 nights in two consecutive years in order to resolve the long-standing ambiguity related to its secondary period. A frequency analysis of almost 5000 individual single-filtered CCD V measurements resulted in two independent frequencies (f1 = 6:6879 d 1 and f2 = 11:8266 d 1 ) with a ratio of f1=f2 = 0:565. Earlier data taken from the literature were used to refine the dominant period, and the re-analysis supports the existence of the secondary period. Possible asteroseismological implications are briefly discussed.