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We present our spectroscopic observations of V455 Andromedae during the 2007superoutburst. Our observations cover this superoutburst from around theoptical peak of the outburst to the post-superoutburst stage. During the earlysuperhump phase, the emission lines of Balmer series, He I, He II, Bowen blend,and C IV / N IV blend were detected. He II 4686 line exhibited a double-peakedemission profile, where Balmer emission lines were single-peaked, which isunexpected from its high inclination. In the ordinary superhump phase, Balmerseries transitioned to double-peaked emission profiles, and high-ionizationlines were significantly weakened. These transitions of the line profilesshould be related to the structural transformation of the accretion disk, asexpected between the early and ordinary superhump transition in thethermal-tidal instability model. The Doppler map of H$\alpha$ during the earlysuperhump phase exhibits a compact blob centered at the primary white dwarf. Inanalogy to SW Sex-type cataclysmic variables, this feature could emerge fromthe disk wind and/or the mass accretion column onto the magnetized white dwarf.The Doppler map of He II 4686 \AA~ is dominated by the ring-like structure andimposed two flaring regions with the velocity of $\sim$300 km/s, which is tooslow for a Keplerian accretion disk. The phase of the flaring regions wascoincident with the inner spiral arm structure identified during the earlysuperhump phase. Our disk wind model with the enhanced emission from the innerarm structure successfully reproduced the observed properties of He II 4686\AA. Therefore, V455 And is the first case in dwarf nova outbursts that thepresence of the disk wind is inferred from an optical spectrum.

Spectroscopic Observations of V455 Andromedae Superoutburst in 2007: the Most Exotic Spectral Features in Dwarf Nova Outbursts