PNV J00444033+4113068: early superhumps with 0.7 mag amplitude and non-red color

TL;DR

This study reports the observation of an eclipsing WZ Sge-type dwarf nova with the largest known early superhump amplitude and unique color behavior, supporting the 2:1 resonance model of accretion disk structure.

Contribution

It provides detailed optical observations and analysis of early superhumps in PNV J00444033+4113068, revealing unique amplitude and color features that enhance understanding of accretion disk resonances.

Findings

Confirmed early superhumps with 0.7 mag amplitude, the largest among known WZ Sge-type DNe.

Discovered the early superhumps become reddest around their secondary minimum, opposite to other DNe.

Spectroscopy indicated a high-inclination system with double-peaked emission lines.

Abstract

In the first days of WZ Sge-type dwarf nova (DN) outbursts, the 2:1 resonance induces a spiral arm structure in the accretion disk, which is observed as early superhumps in optical light curves. This paper reports our optical observations of an eclipsing WZ Sge-type DN PNV J00444033+4113068 during its 2021 superoutburst with the 3.8m Seimei telescope and through VSNET collaboration. The eclipse analysis gave its orbital period as 0.055425534(1) d. Our observations confirmed early superhumps with an amplitude of 0.7 mag, the largest amplitude among known WZ Sge-type DNe. More interestingly, its early superhumps became the reddest around their secondary minimum, whereas other WZ Sge-type DNe show the reddest color around the early superhump maximum. The spectrum around the peak of the outburst showed the double-peaked emission lines of He II 4686\AA~ and H$\alpha$ with a peak separation of $\ge 700$ km/s, supporting a very high-inclination system. With the early superhump mapping, the unique profile and color of the early superhump of PNV J00444033+4113068 are successfully reproduced by the accretion disk with vertically extended double arm structure. Therefore, the large amplitude and unique color behavior of the early superhumps in PNV J00444033+4113068 can be explained by the 2:1 resonance model along with other WZ Sge-type DNe.