The Evolution of the Optical Spectrum of V455 Andromedae throughout the 2007 Superoutburst

V455 And is a dwarf nova with a short orbital period, close to the orbital period minimum. The object underwent its first detected outburst in 2007, brightening from around V = 16.5 all the way to magnitude 8. Outbursts of such amplitude occur exclusively in dwarf novae with short periods (typically P (orb) less than or similar to 90 minutes) and are called superoutbursts. The recurrence time of superoutbursts is long (decades), hence only very few have been studied in detail. We succeeded in observing the entire superoutburst of V455 And spectroscopically from the rise to the decline with unprecedented detail. While the light curve of the object throughout the outburst does not seem to differ much from other dwarf novae, its spectroscopic behavior is strikingly different during the transition stage from the absorption-dominated lines to the strong emission one during the rise. We interpret the emergence of the strong emission lines with little radial velocity variations during the superoutburst as evidence of wind from the evaporating disk in this high-inclination system. The evolution of the line profiles from wide to narrow peak separation during the rise, and back at the decline, matches models showing that the peak separation is a function of optical depth in the lines.

Automated summary

V455 And is a dwarf nova with a short orbital period that underwent a unique superoutburst. The spectroscopic behavior during the rise and decline of the superoutburst suggests the presence of wind from the evaporating disk in this high-inclination system. This observation provides valuable evidence for understanding the dynamics in such systems.