Search for Pulsating Stars in the Globular Cluster M 80 from Ground‐ and Space‐based Observations

We present preliminary results of the search for pulsating stars in the globular cluster M 80 from both ground‐ and space‐based CCD observations. Application of the image subtraction method to the ground‐based times series of CCD frames resulted in finding 9 new RR Lyrae stars: six RRc and three RRab stars. Revised mean period of seven RRab stars, $〈P〉ab = 0.68 d,$ and relative percentage of RRc stars, $Nc/(Nab+Nc) = 53%,$ strongly confirm that M 80 belongs to the Oosterhoff II group of globular clusters. Moreover, we have found 3 SX Phoenicis stars among the cluster’s blue stragglers. In two pulsating stars we discovered oscillations with two close frequencies, which indicates excitation of non‐radial modes. We also used archival HST observations in an attempt for detecting other SX Phoenicis stars mostly in the dense cluster’s core. From the scatter in the U‐filter light curves of observed blue stragglers we identified nine probable SX Phoenicis variables.