Four new eclipsing accreting ultracompact white dwarf binaries found with the Zwicky Transient Facility

Abstract

Accreting ultracompact white dwarf binaries contain a white dwarf that is accreting from a degenerate object. They have orbital periods shorter than 65 minutes. We report the discovery and the orbital period of four new eclipsing accreting ultracompact white dwarf binaries found using the Zwicky Transient Facility (ZTF) and discuss their photometric properties. We searched through a list of 4171 dwarf novae compiled using the ZTF and used the box least square method to search for periodic signals in the data. We found four eclipsing accreting ultracompact binaries with orbital periods between 25.9 and 56 minutes.\ One had previously been published as an AM Canum Venaticorum (AM CVn), and the other three systems are new discoveries. The two shorter-period systems are likely also AM CVn systems, while the longest-period system, with a period of 56 minutes, showed multiple super-outbursts over two years, which is more consistent with it being a helium CV.