On the Colour Variations of Negative Superhumps

TL;DR

This study analyzes the colour variations of negative superhumps in the dwarf nova ER UMa, revealing that brightness maxima align with bluest colour peaks and supporting a tilted disk model as the source.

Contribution

It provides the first simultaneous multi-band photometry of negative superhumps in ER UMa, highlighting distinct properties from positive superhumps and supporting the tilted disk hypothesis.

Findings

Brightness maxima coincide with bluest colour peaks.

Negative superhump amplitudes are largest in the g' band.

Properties differ from early and positive superhumps.

Abstract

We present simultaneous $g'$, $R_{\rm c}$, and $I_{\rm c}$ photometry of the notable dwarf nova ER UMa during the 2011 season. Our photometry revealed that the brightness maxima of negative superhumps coincide with the bluest peaks in $g' - I_{\rm c}$ colour variations. We also found that the amplitudes of negative superhumps are the largest in the $g'$ band. These observed properties are significantly different from those observed in early and positive superhumps. Our findings are consistent with a tilted disk model as the light source of negative superhumps.