Serendipitous Discovery of a Cataclysmic Variable in the Globular Cluster NGC 6624

Abstract

Despite indications that classical cataclysmic variable (CV) stars are rare in globular clusters in general, and in the cluster NGC 6624 in particular, we have serendipitously discovered such a star ~6" from the cluster center. A Hubble Space Telescope spectrum of the m~22 object shows strong, broad emission lines typical of numerous field CVs, and the inferred optical and UV luminosity are also similar. Our accidental observation also provides the first high-quality ultraviolet spectrum of a globular cluster CV. That we have detected such an object in an observation that includes just a few percent of the central area of the cluster may indicate that cluster CVs are more common than previously thought, at least near the core.