# NSV 1440: First WZ Sge-type Object in AM CVn stars and candidates

## TL;DR

This paper reports the discovery of NSV 1440 as the first WZ Sge-type AM CVn star, showing unique early superhumps and rebrightenings, providing insights into its orbital period and mass ratio.

## Contribution

It is the first to confirm an AM CVn star as WZ Sge-type with observed early superhumps, expanding understanding of these systems.

## Key findings

- First observed early superhumps in an AM CVn star.
- Estimated mass ratio q = 0.045, indicating a semi-degenerate secondary.
- Detected multiple rebrightenings after superoutbursts.

## Abstract

In 2015 and 2017, the AM CVn candidate NSV 1440 showed superoutbursts having the characteristic features of WZ Sge-type dwarf novae (DNe). By analogy with hydrogen-rich cataclysmic variables (CVs), we can interpret these outbursts as `double superoutbursts' which are composed of the first superoutburst with early superhumps and the second superoutburst with ordinary superhumps. The object also showed multiple rebrightenings after the main superoutbursts. Early superhumps had been never observed in AM CVn stars and candidates, thus NSV 1440 is the first confirmed WZ Sge-type AM CVn candidate. We obtained the early superhump period of 0.0252329(49) d and the growing (stage A) superhumps period of 0.025679(20) d from the 2015 superoutburst. We regarded the early superhump period as the orbital one. By using these periods we estimated the mass ratio $q = $0.045(2). This value suggests that NSV 1440 is indeed an AM CVn star and that the secondary is a semi-degenerate star.