Photometric Observations of a WZ Sge-type Dwarf Nova V455 Andromedae during the 2007 Superoutburst

We discovered the first outburst of V455 And (=HS2331+3905) on Sep. 4 2007 at V=14.59, which has been considered a good candidate for the WZ Sge-type dwarf nova. A time-resolved photometry campaign was soon coordinated and covered the whole of the superoutburst from the rising phase to the slow fading tail. At the time of our outburst detection, the object was in the rising phase at a rate of 10 mag/day. We found that there were no orbital humps nor early superhumps during the rapid rising phase of superoutburst. Early superhumps with a period of 0.05626(1) days appeared around the maximum. Ordinary superhumps appeared 9 days after the maximum. The superhump period was 0.057202(1) days which was 1.6 decline from the plateau 19 days after the maximum. After the rapid fading, the object showed a slow fading trend at a rate of 0.03 mag/day. During the early phase of the slow fading tail, superhumps with a period of 0.05728(3) days were observed. The object showed no rebrightenings. We will present the results from our observation campaign on this object.