SCOVaS: Survey for Compact Objects and Variables Stars

Globular clusters (GCs) are very old group of stars. Their age and very dense stellar density lead to a higher formation rate of compact binaries (i.e. those harboring black holes, neutron stars, and white dwarfs in tight orbits), compared to the Galactic field. Of special interest are the cataclysmic variables (CVs), which are accreting white dwarfs from hydrogen-rich companions. CVs deserve special attention as they are predicted to account for a large fraction of the compact binary population in GCs and can be used to test whether GCs are in fact the efficient factories of compact binaries that we think. In this talk, I will present the first results of an ongoing survey, which uses archival Hubble Space Telescope data of globular clusters with different characteristics, to do the first search for faint Cataclysmic Variables in Globular clusters that is not biased in the X-rays. I will discuss these results with respect to the models of formation and evolution of CVs, focusing on the predicted number of these binaries and their detectability and how observables can help to constraint existing binary evolutionary models regarding the formation rate, orbital period distribution and spatial distribution of CVs. I will also show how this survey has helped to characterize other exotic binaries, such as obtaining the 2-day orbital period of a candidate redback pulsar in the globular cluster NGC 6397. This is the longest orbital period known for pulsars of that kind in any globular cluster. I will discuss the implications of that result.