New Candidates for AM Canum Venaticorum Stars among ASAS-SN Transients

TL;DR

This study identifies potential AM CVn-type stars among ASAS-SN transients by analyzing ZTF light curves, highlighting distinctive features such as short outbursts and superoutbursts, and proposing a new identification scheme.

Contribution

The paper introduces a method to identify AM CVn candidates based on light curve features, expanding the known candidates among transient surveys.

Findings

Six new AM CVn-type candidates identified.

Distinctive light curve features differentiate AM CVn from hydrogen-rich systems.

Some candidates show long supercycles of several years.

Abstract

We studied Zwicky Transient Facility (ZTF) light curves of 34 dwarf nova candidates discovered by All-Sky Automated Survey for Supernovae (ASAS-SN) between 2020 May 12 and September 9 and found 6 AM CVn-type candidates. All objects showed short outbursts (post-superoutburst rebrightenings) on the fading tail. Two objects (ASASSN-20eq, ASASSN-20la) showed double superoutbursts. Three objects (ASASSN-20jt, ASASSN-20ke, and ASASSN-20lr) showed short superoutbursts (5-6 d). These features in the light curve can be used in discriminating AM CVn-type candidates from hydrogen-rich systems. In contrast to hydrogen-rich systems, some object did not show red color excess during the rebrightening or fading tail phase. We interpret that this is due to the higher ionization temperature in helium disks. Two objects had long (likely) supercycles: ASASSN-20gx (8.5 yr) and ASASSN-20lr (7 yr). We provide a scheme for identifying AM CVn-type candidates based on the light curve characteristics.