EC15330-1403 and the AM CVn stars

Abstract

We report the discovery of the sixth AM CVn star. The object was found in the Edinburgh-Cape blue object survey and is bright (B ∼13.5). Its properties are more like those of the prototype, AM CVn, than like those of any of the other four members of the class: no large changes in brightness have been seen (so far) and the fundamental period of its rapid oscillations is 1119 s. Its optical spectrum shows only broad, shallow He I absorption lines. No rapid radial velocity variations were found; a search for slow, periodic changes in its line profiles was inconclusive. The 1119-s oscillations comprise three components: the fundamental and first two harmonics; no other periodic signals were detected. The properties of the AM CVn stars are discussed in the context of the interacting binary white dwarf model.