Superhumps in active dwarf novae. Part I: ER Ursae Majoris

TL;DR

This study analyzes the superoutburst behavior of ER Ursae Majoris over 30 years, revealing stable superhump periods and a decreasing supercycle length, indicating a declining mass-transfer rate.

Contribution

First detailed long-term photometric analysis of ER UMa's superoutbursts, showing stable superhump period excess and evolving supercycle length over three decades.

Findings

Superhump period excess is approximately 3.0%.

Supercycle length increased from 42.1 to 59.6 days.

Mass-transfer rate appears to be decreasing over 30 years.

Abstract

We report photometry results of a frequently outbursting dwarf nova, ER Ursae Majoris. To measure the outburst parameters of the system, we carried out analyses of the light curve, periodograms, and O-C diagrams. We investigated the system's behaviour using the ground-based optical data and the Transiting Exoplanet Survey Satellite data. During these observation runs, we scrutinised three superoutbursts and several normal outbursts. We detected ordinary and late superhumps during each of the investigated superoutbursts. We derived the period excess value $\epsilon \approx 3.0(1)\% $. This suggests that over the last 30 years, ER UMa has not shifted on the evolutionary path toward period-bounce objects. Between 1992 and 2022, the interval between two successive superoutbursts (the supercycle length) changed significantly from 42.1 days to 59.6 days, which indicates that the mean mass-transfer rate of ER UMa has been decreasing over this period.