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We present spectroscopic and photometric observations of 17 dwarf-novasuperoutbursts obtained by KOOLS-IFU mounted on the 3.8 m telescope Seimei atOkayama Observatory of Kyoto University and through VSNET collaboration. Ourspectroscopic observations for six outbursts were performed within 1 d fromtheir optical peak. 11 objects (TCP J00590972+3438357. ASASSN-19ado, TCPJ06073081-0101501, 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 enabledquick classification of their transient type. These results illustrate thatSeimei telescope has the capability to conduct quick follow-up observations ofunknown transients. Our photometric observations yielded that 11 objects are WZSge-type dwarf novae and their candidates, and the other six objects are SUUMa-type dwarf novae and their candidates. The He II 4686\AA~ emission line wasclearly detected among ASASSN-19ado, TCP J06073081-0101501 and MASTER OTJ213908.79+161240.2, whose association with a spiral arm structure in anaccretion disk has been suggested in the previous studies. Our result suggeststhat a higher-inclination system shows a stronger emission line of He II4686\AA, as well as larger-amplitude early superhumps.

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