A study of transients from ground-based surveys reveals new ultra-compact accreting white dwarf binaries

Authors

• Jan Kára, The University of Texas Rio Grande ValleyFollow
• Liliana E. Rivera Sandoval, The University of Texas Rio Grande ValleyFollow
• Wendy Mendoza, The University of Texas Rio Grande Valley
• Thomas J. Maccarone, Texas Tech University
• Manuel Pichardo Marcano
• Luis Salazar Manzano, University of Michigan
• Ryan J. Oelkers, The University of Texas Rio Grande ValleyFollow
• Jan van Roestel

Document Type

Article

Publication Date

3-27-2026

Abstract

AM CVn stars are ultra-compact semi-detached binaries consisting of a white dwarf primary and a hydrogen-depleted secondary. In this paper, we present spectroscopic and photometric results of 15 transient sources pre-classified as AM CVn candidates. Our analysis confirms 9 systems of the type AM CVn, 3 hydrogen-rich cataclysmic variables (accreting white dwarfs with near-main-sequence stars for donors), and 3 systems that could be evolved cataclysmic variables. Eight of the AM CVn stars are analysed spectroscopically for the first time, which increases the number of spectroscopically confirmed AM CVns by about 10%. TESS data revealed the orbital period of the AM CVn star ASASSN-20pv to be 𝑃orb =27.282 min, which helps to constrain the possible values of its mass ratio. TESS also helped to determine the superhump periods of one AM CVn star (ASASSN-19ct, 𝑃sh =30.94 min) and two cataclysmic variables we classify as WZ Sge stars (𝑃sh =90.77 min for ZTF18aaaasnn and 𝑃sh =91.6 min for ASASSN-15na). We identified very different abundances in the spectra of the AM CVns binaries ASASSN-15kf and ASASSN-20pv (both 𝑃orb ∼27.5 min), suggesting different type of donors. Six of the studied AM CVns are X-ray sources, which helped to determine their mass accretion rates. Photometry shows that the duration of all the superoutbursts detected in the AM CVns is consistent with expectations from the disc instability model. Finally, we provide refined criteria for the identification of new systems using all-sky surveys such as LSST.

Comments

© The Author(s), 2026. Published by Cambridge University Press on behalf of Astronomical Society of Australia  

Recommended Citation

Kára, Jan, Liliana Rivera Sandoval, Wendy Mendoza, Thomas J. Maccarone, Manuel Pichardo Marcano, Luis E. Salazar Manzano, Ryan J. Oelkers, and Jan van Roestel. "A study of transients from ground-based surveys reveals new ultra-compact accreting white dwarf binaries." Publications of the Astronomical Society of Australia (2026): 1-28. https://doi.org/10.1017/pasa.2026.10184

Creative Commons License

This work is licensed under a Creative Commons Attribution 4.0 International License.

Publication Title

Publications of the Astronomical Society of Australia

DOI

10.1017/pasa.2026.10184