A Distinct Type of Standstill in Ultra-Compact White Dwarf Binaries
Abstract
AM CVn stars are ultra-compact, semi-detached binaries consisting of a white dwarf primary and a hydrogen-poor secondary. In this work, we analyse the AM CVn-type systems MGAB-V270, ZTF18aaxuusk and ASASSN-19ct, which have similar properties and show unusual post-superoutburst behaviour. We focus on the occurrence of standstill-like phases. In MGAB-V270, superoutbursts are followed by a series of echo outbursts that evolves into a standstill-like phase before the system returns to quiescence. ZTF18aaxuus shows similar post-superoutburst activity, with one echo-outburst series also developing into a standstill-like phase. ASASSN-19ct exhibits comparable echo outbursts but no standstill-like phases. Periodicity analysis using TESS data shows that superhumps can persist during both echo outbursts and standstill-like phases. Although standstills have previously been observed in AM CVn stars, the standstill-like phases we observe appear to represent a distinct phenomenon associated with post-superoutburst activity. We compare our results to other AM CVns that may exhibit similar behaviour.
Related
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BibTeX
@misc{kara2026distinct,
title = {{A Distinct Type of Standstill in Ultra-Compact White Dwarf Binaries}},
author = {Jan Kára and Liliana Rivera Sandoval and Iwona Kotko and Jean-Marie Hameury and Luis E. Salazar Manzano and Ryan J. Oelkers},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.19105},
eprint = {2610.19105},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.19105},
}
RIS
TY - UNPB
TI - A Distinct Type of Standstill in Ultra-Compact White Dwarf Binaries
AU - Jan Kára
AU - Liliana Rivera Sandoval
AU - Iwona Kotko
AU - Jean-Marie Hameury
AU - Luis E. Salazar Manzano
AU - Ryan J. Oelkers
PY - 2026
DA - 2026/10/13
PB - arXiv
DO - 10.48550/arxiv.2610.19105
UR - https://arxiv.org/abs/2610.19105
AB - AM CVn stars are ultra-compact, semi-detached binaries consisting of a white dwarf primary and a hydrogen-poor secondary. In this work, we analyse the AM CVn-type systems MGAB-V270, ZTF18aaxuusk and ASASSN-19ct, which have similar properties and show unusual post-superoutburst behaviour. We focus on the occurrence of standstill-like phases. In MGAB-V270, superoutbursts are followed by a series of echo outbursts that evolves into a standstill-like phase before the system returns to quiescence. ZTF18aaxuus shows similar post-superoutburst activity, with one echo-outburst series also developing into a standstill-like phase. ASASSN-19ct exhibits comparable echo outbursts but no standstill-like phases. Periodicity analysis using TESS data shows that superhumps can persist during both echo outbursts and standstill-like phases. Although standstills have previously been observed in AM CVn stars, the standstill-like phases we observe appear to represent a distinct phenomenon associated with post-superoutburst activity. We compare our results to other AM CVns that may exhibit similar behaviour.
ER -