TCP J07222683$+$6220548: a new AM CVn type system with infrequent outbursts

TL;DR

The paper reports the discovery and detailed observation of TCP J07222683+6220548, a new AM CVn ultracompact binary system with infrequent outbursts, characterized by positive superhumps and rebrightenings, expanding understanding of such systems.

Contribution

This work presents the first detailed detection and analysis of an AM CVn system with infrequent outbursts, highlighting the importance of follow-up observations for proper classification.

Findings

Discovered a new AM CVn system with a 7-day outburst

Detected positive superhumps with a period of ~46.87 minutes

Identified rebrightenings and stable superhump periods

Abstract

We present the discovery of TCP J07222683$+$6220548, a new ultracompact binary system of the AM CVn type. This system was first identified displaying a $\Delta V = 7.6$ mag outburst on 2025-01-20.9416 UTC by the New Milky Way wide-field survey for transients and later independently detected by ASAS-SN and ZTF. The outburst peaked at $V_{\rm max} = 12.45$ and lasted for seven days, followed by a series of rebrightenings. No previous outbursts are found in archival data. Positive superhumps with a period of $0.032546 \pm 0.000084$ d ($46.87 \pm 0.12$ min), barely detectable during the main outburst, became clearly visible during the first rebrightening that lasted from day 18 to day 24 after the initial outburst. No convincing change in the superhump period was detected. Dense time-series photometry follow-up by a pair of 0.5-m INASAN robotic telescopes, together with VSNET and AAVSO observers, was essential for identifying TCP J07222683$+$6220548 as an AM CVn system and triggering confirmation spectroscopy with the 2.5-m CMO SAI telescope. Some outbursting AM CVn systems lacking such detailed follow-up may remain unrecognized among the newly discovered cataclysmic variable candidates.