Optical pulsations in the cataclysmic binary 3A 0729+103

Abstract

Fast photometric observations of the newly discovered cataclysmic variable 3A 0729+103 are reported. Regular optical pulsations, with an average semiamplitude of ~0.15 mag in B-band and having a period in agreement with that reported by McHardy et al. (1982) are clearly detected in the light curve of the star. The optical pulse has a sinusoidal shape. Flares with a maximum amplitude of ~0.43 mag have also been observed. There is also suggestion of flickering on time scales of ≧10s. It is suggested that 3A 0729+103 is similar in characteristics to H 2252-035 class of cataclysmic binaries containing rapidly rotating white dwarfs. Interpretation of the period of optical pulse as the beat period leads to prediction of X-ray pulse period to be about 847s for prograde rotation and 991s for retrograde rotation of the white dwarf compared to the reported ~900-1000s period. Alternative interpretation of the observed optical pulse being due to directly beamed radiation from the vicinity of the pole of the white dwarf is also considered.