A New WZ Sagittae-type Dwarf Nova KSP-OT-202104a Near the Period Minimum from the KMTNet Supernova Program

TL;DR

This paper reports the discovery and analysis of a new WZ Sagittae-type dwarf nova with a very short orbital period, providing insights into systems near the period minimum and potential evolution toward AM CVn stars.

Contribution

It presents the first detailed photometric and spectroscopic characterization of KSP-OT-202104a, a dwarf nova likely below the period minimum, expanding understanding of short-period cataclysmic variables.

Findings

The nova exhibits an 8 mag outburst lasting about 28.5 days.

The superhump period is approximately 71.7 minutes, indicating a very short orbital period.

Spectroscopy shows a blue continuum with hydrogen absorption lines, typical of outbursting DNe.

Abstract

We present photometric and spectroscopic studies of a new WZ Sagittae (Sge)-type dwarf nova (DN) KSP-OT-202104a discovered by the Korea Microlensing Telescope Network Supernova Program. The source exhibits outburst amplitudes of $\sim 8$ mag with a duration of $\sim 28.5$ days in the $V$-band. It is a type D DN among WZ Sge-types, and we estimate the superhump period to be $P_{\rm sh} \approx 71.7$ minutes ($=0.04978$ days). Its spectrum shows blue continuum as often found in optically-thick accretion disks of DNe during outbursts with hydrogen absorption lines from H$\beta$ to H$\zeta$. Since the orbital period in WZ Sge-type DNe is typically very close to the superhump period, we consider that this target would belong to the small sample of DNe below the period minimum and may be evolving toward AM Canum Venaticorum (AM CVn) stars. This system therefore adds an example of a short-period dwarf nova with a low mass-transfer rate to the known sample.