CS Indi: SU UMa-Type Dwarf Nova with Long Precursor Outburst

TL;DR

This study documents a rare long precursor outburst in a SU UMa-type dwarf nova, CS Ind, revealing insights into the slow development of tidal instability and its effects on superoutburst characteristics.

Contribution

First observation of a long precursor in a SU UMa-type dwarf nova, supporting theories on tidal instability development near the 3:1 resonance.

Findings

Confirmed long superhump period of 0.12471 days

Identified long precursor outburst before superoutburst

Supported slow tidal instability development hypothesis

Abstract

We observed the 2018 November outburst of CS Ind and confirmed that it was a genuine superoutburst with a very long [0.12471(1) d in average] superhump period. The superoutburst was preceded by a long precursor, which was recorded first time in SU UMa-type dwarf novae. We interpret that the combination of a sufficient amount of mass in the disk before the ignition of the outburst and the slow development of tidal instability near the borderline of the 3:1 resonance caused a cooling front to start before the full development of tidal instability. This finding provides another support to the recent interpretation of slow development of the tidal instability causing various phenomena similar to WZ Sge-type dwarf novae in SU UMa-type dwarf novae with very long orbital periods.