Photometric and spectroscopic Studies of Superoutbursts of Three Dwarf Novae Independently Identified by The SVOM/GWAC System in 2018

TL;DR

This study presents photometric and spectroscopic analyses of three dwarf novae superoutbursts, revealing their classifications, mass ratios, and emission region properties, thereby enhancing understanding of their physical characteristics.

Contribution

It provides detailed observational data and analysis of three dwarf novae, including their classification, mass ratios, and emission region properties, based on photometric and spectroscopic follow-up.

Findings

GWAC 180415A is a WZ Sge-type dwarf nova with long duration and rebrightenings.

GWAC 181211A is a WZ Sge-type candidate based on mass ratio and location.

Balmer line emission regions differ between the three objects.

Abstract

We report our photometric and spectroscopic follow-up observations of the superoutbursts of three dwarf novae (GWAC\,180415A, GWAC\,181017A and GWAC\,181211A) identified independently by the Ground Wide-angle Cameras system, one of the ground-based instruments of the China-France SVOM mission. Based on a combination of our photometry and that taken from the AAVSO, our period analysis of the superhumps enables us to determine the mass ratios to be 0.0967-0.1163, 0.1879-0.1883 and 0.0981-0.1173 for GWAC\,180415A, GWAC\,181017A and GWAC\,181211A, respectively. GWAC\,180415A can be firmly identified as a WZ sge-type dwarf novae due to its long duration ($\sim2$ weeks) multiple rebrightenings with amplitudes of 3-4 magnitudes, the early superhump associated with a double-wave modulation and the low mass ratio. The inferred low mass ratio and location in the $\varepsilon-P_{\mathrm{orb}}$ diagram suggest that GWAC\,181211A is a WZ sge-type dwarf novae candidate. The measured Balmer decrements suggest the Balmer line emission is produced from an optical thick region in GWAC\,180415A and GWAC\,181017A, and from an optical thin region in GWAC\,181211A.