Spectroscopic and Photometric Observations of Dwarf Nova Superoutbursts by the 3.8 m Telescope Seimei and the Variable Star Network

TL;DR

This study reports spectroscopic and photometric observations of 17 dwarf nova superoutbursts, demonstrating the Seimei telescope's capability for quick transient follow-up and classifying the systems into WZ Sge-type and SU UMa-type categories.

Contribution

First comprehensive spectroscopic and photometric analysis of multiple dwarf nova superoutbursts using the Seimei telescope, enabling rapid classification of unknown transients.

Findings

11 objects identified as WZ Sge-type dwarf novae

6 objects identified as SU UMa-type dwarf novae

Higher-inclination systems show stronger He II 4686Å emission and larger early superhump amplitudes

Abstract

We present spectroscopic and photometric observations of 17 dwarf-nova superoutbursts obtained by KOOLS-IFU mounted on the 3.8 m telescope Seimei at Okayama Observatory of Kyoto University and through VSNET collaboration. Our spectroscopic observations for six outbursts were performed within 1 d from their optical peak. 11 objects (TCP J00590972+3438357. ASASSN-19ado, TCP J06073081-0101501, ZTF20aavnpug, ASASSN-19ady, MASTER OT J061642.05+435617.9, TCP J20034647+1335125, ASASSN-20kv, ASASSN-20kw, MASTER OT J213908.79+161240.2, and ASASSN-20mf) were previously unknown systems, and our observations enabled quick classification of their transient type. These results illustrate that Seimei telescope has the capability to conduct quick follow-up observations of unknown transients. Our photometric observations yielded that 11 objects are WZ Sge-type dwarf novae and their candidates, and the other six objects are SU UMa-type dwarf novae and their candidates. The He II 4686\AA~ emission line was clearly detected among ASASSN-19ado, TCP J06073081-0101501 and MASTER OT J213908.79+161240.2, whose association with a spiral arm structure in an accretion disk has been suggested in the previous studies. Our result suggests that a higher-inclination system shows a stronger emission line of He II 4686\AA, as well as larger-amplitude early superhumps.