Optical photometrical observations and variability for quasar 4C 29.45

We reported the result of the long-term optical variability of the blazar 4C 29.45s (QSO 1156 + 295, Ton 599), carried out by optical photometric observations in the Johnson V, Cousins RI passbands during 1997 April to 2002 March. We used the 1.56-m telescope of the Shanghai Astronomical Observatory at Sheshan, China, and compiled the post-1974 optical photometric data of the blazar by combining our new observations with the published optical data, and found maximum variations in different passbands: Delta U = 4.41 mag, Delta B = 5.55 mag, Delta V = 4.53mag, Delta R = 5.80mag, and Delta I = 5.34mag. The average color indices are: U - B = -0.54 +/- 0.18 mag, B - V = 0.56 +/- 0.21 mag, B - R = 0.93 +/- 0.18mag, B - I = 1.51 +/- 0.24mag, V - R = 0.44 +/- 0.15mag, and V - I = 1.03 +/- 0.23mag. The post-1974 data give us an excellent opportunity to search for the existence of a possible periodicity in the light curve. In searching for periodicity in the R passband light curve, we performed a Jurkevich test and power spectral (Fourier) analysis methods, as well as CLEANest algorithms to remove false signals. We found possible periods of 3.55 and 1.58 years. A possible mechanism for the periodic variability was analyzed.