Photometric Observations of an SU UMa-type Dwarf Nova, VW Coronae Borealis, during Outbursts

We report the photometric observations of an SU UMa-type dwarf nova VW CrBduring two superoutbursts in 2001 and 2003 and a normal outburst in 2003.Superhumps with a period of 0.07287(1) d were observed during the 2003superoutburst. The change rate of the superhump period was positive. During thenormal outburst, there are some hint of modulation up to a 0.2-mag amplitude.However, any periodicity was not found. The recurrence cycles of the normaloutburst and the superoutburst, and the distance were estimated to be > ~50 d,270-500 d, and 690(+230, -170) pc, respectively. These recurrence cycles areusual values for an SU UMa-type dwarf nova having this superhump period. Thesuperhump period of VW CrB was the longest among those of the SU UMa stars withpositive derivatives of the superhump period. The coverage of our observationswas, however, not enough, and the variation of the Psh change rate of VW CrB isstill unknown. A superhump regrowth and a brightening were seen near the end ofthe plateau phase. Measuring the deviation of the start timings of thebrightening and the superhump regrowth (>2 days in VW CrB) will be a key toreveal the mechanism of these phenomena.Comment: 7 pages, 8 figures, to appear in PAS