Letter to the Editor

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

¹ Anton Pannekoek Institute for Astronomy, University of Amsterdam, 1090 GE Amsterdam, The Netherlands
e-mail: j.c.j.vanroestel@uva.nl
² DIRAC Institute, Department of Astronomy, University of Washington, 3910 15th Avenue NE, Seattle, WA 98195, USA
³ Department of Astrophysics, University of California, Berkeley, CA 94720-3411, USA
⁴ Lawrence Berkeley National Laboratory, 1 Cyclotron Road, MS 50B-4206, Berkeley, CA 94720, USA
⁵ Caltech Optical Observatories, California Institute of Technology, Pasadena, CA 91125, USA
⁶ Division of Physics, Mathematics, and Astronomy, California Institute of Technology, Pasadena, CA 91125, USA
⁷ IPAC, California Institute of Technology, 1200 E. California Boulevard, Pasadena, CA 91125, USA

Received: 19 December 2023
Accepted: 15 February 2024

Abstract

Context. Accreting ultracompact white dwarf binaries contain a white dwarf that is accreting from a degenerate object. They have orbital periods shorter than 65 min.

Aims. 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.

Methods. 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.

Results. We found four eclipsing accreting ultracompact binaries with orbital periods between 25.9 and 56 min. 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 min, showed multiple super-outbursts over two years, which is more consistent with it being a helium CV.