Discovery and characterization of ZTF J0112+5827: An 80.9-minute polar with strong cyclotron features

Abstract

We report the discovery and characterization of ZTF J0112+5827, a new magnetic cataclysmic variable with an orbital period of 80.9 minutes. ROSAT observations revealed X-ray emission with an average flux of $(68.4\pm 15.7)\times 10^{-14}$ erg s${}^{-1}$ cm${}^{-2}$ (0.1--2.4 keV). The ZTF light curves show ellipsoidal-like variability in the $g$ band and two prominent humps at phases $\sim$0.0 and $\sim$0.7 in $i$ and $r$ bands. Spectroscopic observations with the Palomar 200-inch telescope revealed cyclotron emission features and strong He II and Balmer emission lines. Doppler tomography shows clear accretion streams with line-of-sight velocities of $\sim$500 km s${}^{-1}$, but no accretion disk. Analysis of cyclotron harmonics indicates a magnetic field strength of $38.7_{-1.1}^{+1.3}$ MG, confirming ZTF J0112+5827 as a polar system containing a strongly magnetic white dwarf.