Detection of Change in Supercycles in ER Ursae Majoris

TL;DR

This study analyzes 20 years of observational data on ER UMa to detect changes in its supercycle length, revealing systematic variations and their possible link to negative superhumps, supporting thermal-tidal instability theory.

Contribution

It provides the first detailed analysis of supercycle variations in ER UMa over two decades, linking observed changes to superhump phenomena and confirming theoretical predictions.

Findings

Supercycle length varies between 43.6 and 59.2 days.

Supercycle variation timescale ranges from 300 to 1900 days.

Number of normal outbursts per supercycle varies from 4 to 6.

Abstract

We examined data on about 20 years of observations of ER UMa available in AAVSO, VSNET, AFOEV, NSVS, VSOLJ databases together with published light curves. The obtained O-C diagram revealed a systematic change of the supercycle (time interval between two successive superotbursts) within 43.6 and 59.2 d. The time-scale of this change variation is from 300 to $\sim$ 1900 d. The number of normal outbursts within the supercycles also varied from 4 to 6 although no strong correlation between this number and supercycle length was found. We suggest that appearance of negative superhumps is responsible for the observed variations of number of normal outbursts. Our results generally confirms the expectations by the thermal-tidal instability theory.