Unusual Outbursting State of a Z Cam-Type Star HL CMa

Abstract

HL CMa is a Z Cam-type dwarf nova which was discovered as an Einstein X-ray source. In addition to normal outbursts and standstills, we noticed the presence of "the third" outbursting state. During this period, the star showed weak outbursts with a long outburst cycle length. We propose that this phenomenon is caused by a heating on the accretion disk. The presence of strong P Cyg feature in the ultraviolet and the unusual presence of high-excitation optical lines could be interpreted as an emerging signature of strong irradiation field. Since the object is still in this unusual state in 2002 March, we encourage X-ray and spectroscopic observations to detect further signatures of high-energy photons and irradiation.

4 pages, 3 figures