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We report the results of photometry of the WZ Sge-type dwarf nova V455 And.Observations were obtained over 19 nights in 2013 and 2014. The total durationof the observations was 96 h. We clearly detected three coherent oscillationswith periods of 80.376+/-0.003 min, 40.5431+/-0.0004 min and67.619685+/-0.000040 s. The 67.619685-s period can be the spin period of thewhite dwarf. The 40.5431-minute period is the first harmonic of the orbitalperiod. The 80.376-minute oscillation can be a negative superhump because itsperiod is 0.9% less than the orbital period. This oscillation was evident bothin the data of 2013 and in the data of 2014. These results make V455 And apermanent superhump system which shows negative superhumps. This is also thefirst detection of persistent negative superhumps in a WZ Sge-type dwarf nova.In addition, the analysis of our data revealed incoherent oscillations withperiods in the range 5-6 min, which were observed earlier and accounted for bynon-radial pulsations of the white dwarf. Moreover, we clearly detected anoscillation with a period of 67.28+/-0.03 s, which was of a low degree ofcoherence. This oscillation conforms to the beat between the spin period of thewhite dwarf and the 3.5-h spectroscopic period, which was discovered earlierand accounted for by the free precession of the white dwarf. Because the67.28-s period is shorter than the spin period and because the free precessionof the white dwarf is retrograde, we account for the 67.28-s oscillation by thefree precession of the white dwarf.

new astronomy

Extensive photometry of the WZ Sge-type dwarf nova V455 And  (HS2331+3905): detection of negative superhumps and coherence features of the  short-period oscillations