UV observations of X-ray sources 2A0311–227 and 2A0526–328

Abstract

The AM Herculis-type of dwarf novae have emerged as a new class of cataclysmic variables. They are characterized by fairly steady accretion from a late-type primary on to a strongly magnetized white dwarf. The progenitor of this group, AM Herculis, shows strong optical polarization¹ and prominent emission lines in both the optical² and the UV³. It is also a hard X-ray^4–6 and an IR source². Two other X-ray sources, 2A0311–227 (ref. 7) and 2A0526–328 (ref. 8), have recently been suggested as members of the AM Her class on the strength of their similar optical spectra. To compare these objects with AM Her and to extend investigations of this new class of dwarf novae the International Ultraviolet Explorer (IUE) satellite was used to obtain their UV spectra and to search for any changes with the binary motion. We show here that the results confirm the identification of 2A0311–227 with the AM Her class, but not 2A0526–328 which seems to exhibit a UV spectrum more consistent with an SS Cygni type object. Changes in the emission lines' intensities of at least a factor of two were observed as a function of the binary phase.