BVR photometry of comets 63P/Wild 1 and C/2012 K1 (PANSTARRS)

We analyzed the BVR photometry of the comets 63P/Wild 1 and C/2012 K1 (PANSTARRS) obtained between March 2013 and May 2014, with 0.20-m to 2.0-m aperture telescopes installed in Australia, Europa and USA. We have found R-band nuclear magnitudes H 0 = 16.3 ± 0.6 and 12.52 ± 0.02 for 63P and K1 comets. Admitting a geometric albedo equal to 0.04, the nuclei have a radius equal to 1.5 ± 0.4 and 8.67 ± 0.08 km respectively. Using the Lomb-Scargle periodogram, we found that the most probable periods of rotation of these nuclei are 14 ± 2 h and 9.4 ± 0.4 h, with a peak-to-peak light curve amplitude of 0.85 ± 0.01 and 0.4 ± 0.2 magnitudes. The inner coma of both comets were probably optically thin and in steady-state during all duration of our observations seasons. The average normalized reflectivity gradient S’ of the coma of 63P and K1 are 10 ± 15 (1 σ ) and 8 ± 7 %/100 nm in the spectral range between 440 and 647 nm, which have indicated that both comets are statistically redder than the Sun. The Kruskal–Wallis H-test suggests that the distribution of the color indexes B-V, V-R, and B-R of the objects are similar, indicating some kind of equality between the physical or mineralogical properties of the comas of these comets.