Photometric and spectroscopic investigations of the Galactic field RRc candidates V764 Mon and HY Com

Abstract

By analyzing photometric and spectroscopic time series in this paper, we show that the pulsator V764 Mon, assumed to be the brightest RR Lyrae star in the sky, is in fact a rapidly rotating delta Scuti star with an unusually long dominant period (P1=0.29 d). Our spectroscopy confirmed the discovery of the Gaia satellite about the binarity of V764 Mon. In the case of HY Com, a `bona fide' RRc star, we present its first complete radial velocity curve. Additionally, we found that the star continues its strong phase variation reported before.