Searching for Ultracompact White Dwarf Binaries in Globular Clusters

Ultracompact white dwarf binaries or AM CVns are interacting hydrogen-poor binary star systems in short orbital periods consisting of either (i) two white dwarfs or (ii) a white dwarf and a helium-rich star. These systems are important for the studies of low-frequency gravitational waves and are expected to be progenitors of Type Ia Supernova. Moreover, AM CVns play a crucial role for the calibration of models employed in the study of binary star evolution. Due to stellar interactions, models suggest that the formation of AM CVns should be enhanced in globular clusters (GCs). However, no AM CVn has been confirmed to exist in a GC so far. We are doing the first dedicated search of outbursting AM CVns systems in the massive and low extinction GC 47 Tucanae using UV Hubble Space Telescope observations. We seek to identify them via their variable behavior and thus confirm that AM CVns can survive stellar interactions in GCs as models predict