2023/07/18 by Taichi Kato, Kato, Taichi
Decision Sciences · Physics and Astronomy · #Astrophysical Phenomena and Observations #FOS: Physical sciences #Gamma-ray bursts and supernovae #Scientific Measurement and Uncertainty Evaluation #Solar and Stellar Astrophysics (astro-ph.SR)
paper · pdf · doi:10.48550/arxiv.2307.08954
openalex publication_date 2023/07/18 · openalex created_date 2023/07/20 · openalex updated_date 2026/08/04
SDSS J183131.63+420220.2 is an AM CVn-type cataclysmic variable. Using Asteroid Terrestrial-impact Last Alert System (ATLAS) and Zwicky Transient Facility (ZTF) data, I found that this object is actually a helium dwarf nova, which experienced a long (~6 yr) standstill (2017 to 2022). The object is currently (in 2023) in ER UMa-type state with supercycles of 20-30 d and large duty cycles exceeding 0.5. This object is the second known star among AM CVn stars having characteristics of ER UMa and Z Cam types. The long duration of the standstill phase is outstanding among helium dwarf novae. These observations indicate that the accretion disk in SDSS J183131.63+420220.2 is very close to thermal stability. I detected a period of 0.01602343(1) d in the ZTF data, which can be the orbital one. Combined with the case of MGAB-V240, the limit of thermal stability of the disks in AM CVn stars appears to be located around the orbital period of 0.0158-0.0160 d.