MASTER OT J055845.55+391533.4: SU UMa star with a dip and long rebrightening

TL;DR

This study analyzes the superoutburst behavior of MASTER OT J055845.55+391533.4, revealing unique dip and rebrightening features that suggest it may belong to a new class of SU UMa-type dwarf novae with distinctive rebrightening phenomena.

Contribution

The paper identifies a new rebrightening pattern in a SU UMa star, proposing it as a potential new class of dwarf nova with unique superoutburst characteristics.

Findings

Superoutbursts show a dip followed by long rebrightening.

Superhump period established at 0.05509 days.

Dip feature may indicate a new subclass of SU UMa-type dwarf novae.

Abstract

We analyzed Asteroid Terrestrial-impact Last Alert System (ATLAS), Zwicky Transient Facility (ZTF) and All-Sky Automated Survey for Supernovae (ASAS-SN) data of MASTER OT J055845.55+391533.4 and found that this object repeats superoutburst with a dip in the middle of the outburst followed by long and sometimes oscillating rebrightening, just like a WZ Sge-type dwarf nova or an AM CVn-type object. The mean supercycle was 298(8) d, too short for a WZ Sge star, but with only a few normal outbursts. We also observed the 2023 February-March superoutburst and established the superhump period of 0.05509(2) d. This period appears to exclude the possibility of an AM CVn star. Although the 2023 observations could not detect superhumps after the dip, the 2014, 2016 and 2021 data seem to suggest that low-amplitude superhumps were present during the rebrightening phase. We note that a dip during a superoutburst is a feature common to the unusual SU UMa-type dwarf nova MASTER OT J172758.09+380021.5 during some of its superoutbursts. These objects may comprise a new class of rebrightening phenomenon in SU UMa-type dwarf novae.