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

摘要

We report our photometric and spectroscopic follow-up observations of the superoutbursts of three dwarf novae (DNe; 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 American Association of Variable Star Observers, 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 DNe due to its long duration (similar to 2 weeks) multiple rebrightenings with amplitudes of 3-4 mag, the early superhump associated with a double-wave modulation and the low-mass ratio. The inferred low-mass ratio and location in the diagram suggest that GWAC 181211A is a WZ sge-type DNe 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 optically thin region in GWAC 181211A.