Eclipse mapping the flickering sources in the dwarf nova HT Cassiopeia

TL;DR

This study uses eclipse mapping to analyze flickering sources in HT Cas, revealing high disc viscosity and suggesting outbursts are driven by increased mass transfer, challenging the disc-instability model.

Contribution

It provides new insights into the flickering sources and viscosity of HT Cas's accretion disc, proposing a different outburst mechanism from traditional models.

Findings

High viscosity in HT Cas's disc (alpha ~ 0.3-0.7)

Rapid white dwarf response to mass transfer changes

Outbursts caused by enhanced mass transfer, not disc instability

Abstract

We report results of the eclipse mapping analysis of an ensemble of light curves of HT Cas. The fast response of the white dwarf to the increase in mass transfer rate, the expansion rate of the accretion disc at the same time, and the relative amplitude of the high-frequency flickering indicate that the quiescent disc of HT Has has high viscosity, alpha ~ 0.3-0.7. This is in marked disagreement with the disc-instability model and implies that the outbursts of HT Cas are caused by bursts of enhanced mass-transfer rate from its donor star.