A spectroscopic and photometric study of 1H 0542-407 : a new magneticvariable.

The authors report spectroscopic and photometric observations of the new DQ Herculis system 1H0542-407, recently discovered by them to be the optical counterpart of a HEAO-1 X-ray source. Medium resolution spectroscopy shows radial velocity variations at periods of ≡1910 s, consistent with the white dwarf rotation period, and 5.7 h, in agreement with the orbital period derived from the authors' EXOSAT observations. A model is developed for 1H0542-407 which indicates that the accretion disk is disrupted at ≡5 R_wd by the primary's magnetic field. The short period velocity variations arise within the magnetosphere. A white dwarf magnetic field strength of <≡3 MG is implied.