H0538 + 608 - A bright AM Herculis-type X-ray source

Abstract

The authors report the discovery of an AM Herculis-type magnetic variable, H 0538+608. The object was located during a program to optically identify the X-ray sources detected with HEAO 1. The X-ray flux (2 - 10 keV) of H 0538+608 is exceeded by only two of the 10 previously observed AM Herculis-type systems. The optical spectrum shows very strong and broad emission lines of H, He I and He II. Photometric observations show modulations by a factor of 2, with B magnitudes between 15 and 16, and the source exhibits rapid flickering at a time scale of 10 s. Circular polarization measurements indicate variable optical polarization between 0 and 10%. The modulations in the polarization and the photometric magnitude suggest an orbital period of 3.1±0.2 hr.