Evolution of the Quiescent Disk surrounding a Superoutburst of the Dwarf Nova TW Virginis

TL;DR

This study models the quiescent disk evolution of dwarf nova TW Virginis using Kepler K2 light curves, revealing consistent disk configurations and hotspot behaviors before and after superoutbursts, with implications for CV evolution models.

Contribution

It provides detailed light curve modeling of TW Virginis's quiescent disk, identifying hotspot dynamics and disk temperature distribution changes around superoutbursts, advancing understanding of dwarf nova behavior.

Findings

Consistent disk and hotspot configuration across observations.

Hotspot temperature and coverage change before and after superoutburst.

Disk temperature distribution remains flat and becomes flatter approaching outburst.

Abstract

Portions of the Kepler K2 Short Cadence light curve of the dwarf nova (DN) TW Vir at quiescence are investigated using light curve modeling. The light curve was separated into 24 sections, each with a data length of $\sim\,$0.93\,d, comprising 4 sections before and 20 after a superoutburst (SO). Due to the morphological differences, the quiescent orbital modulation is classified into three types. Using a fixed disk radius and the two component stellar parameters, all 24 synthetic disk models from the sections show a consistent configuration, consisting of a disk and two hotspots: one at the vertical side of the edge of the disk and the other one on the surface of the disk. Before the SO, the disk and a ringlike surface-hotspot are suddenly enhanced, triggering a precursor and then SO. At the end of the quiescent period following the SO and before the first normal outburst, the edge-hotspot becomes hotter, while the surface-hotspot switches into a ``coolspot" with a coverage of nearly one-half of the disk surface. During quiescence, the surface-hotspot is always located at the outer part of the disk with a constant radial width. A flat radial temperature distribution of the disk is found and appears flatter when approaching the outburst. Like many U\,Gem-type DN with orbital periods of 3-5\,hr, the mass transfer rate is significantly lower than the predictions of the standard/revised models of CV evolution.