GSC 08227-00723: An Unusually Large PSH Excess AH Pic Candidate

TL;DR

This study analyzes the CV candidate GSC 08227-00723, revealing recurrent small outbursts, large superhump excess, and potential tidal effects, classifying it as a new AH Pic-type nova-like star.

Contribution

It provides the first detailed time-domain analysis of GSC 08227-00723, identifying unique superhump excess and outburst features that suggest tidal influences.

Findings

Recurrent low-amplitude outbursts every 30-50 days.

Detection of a large superhump excess of approximately 0.19.

Identification of quasi-periodic oscillations in the light curves.

Abstract

Nova-like variables are high-accretion-rate cataclysmic variables (CVs) that, in contrast to dwarf novae, do not undergo outbursts caused by thermal-viscous instability. However, a small group of nova-likes, classified as AH Pic-type stars, show recurrent small-amplitude outbursts, which are unexpected by the classical disk instability model. The physical mechanisms underlying these outbursts are not clear. In this study, we present a comprehensive time-domain analysis of the CV candidate GSC 08227-00723 using photometric data from ASAS-SN and TESS. The long-term light curves reveal a sequence of low-amplitude, recurrent stunted outbursts with recurrence times ranging from 30 to 50 days. Notably, these outbursts are frequently preceded by precursor brightenings, a feature reminiscent of super-outbursts in SU UMa stars driven by tidal instability. Period analysis of high-cadence TESS data identifies a coherent periodic modulation at 0.297 d, likely the orbital period, and a persistent positive superhump signal at 0.352 d. The latter corresponds to an exceptionally large superhump excess of $\epsilon^+ \approx 0.19$, surpassing typical values seen in CVs. Additionally, we detect short-timescale variability resembling quasi-periodic oscillations in the TESS light curves. Based on the outburst properties and photometric behavior, we classify GSC 08227-00723 as a new member of the AH Pic subclass of nova-like stars. We discuss how tidal effects may be involved in the observed behavior, although the exact mechanism is still unclear.