Photometric BVR observations of comet C/2012 J1 (Catalina) before and after perihelion

Abstract

We analyzed the BVR photometry of comet C/2012 J1 (Catalina) taken between March 2013 and May 2014 with telescopes ranging from 0.20 to 2.0 m aperture in Australia, Europe, and the United States. We found an absolute magnitude in the R-band of H 0 = 7.2 ± 0.1 measured with a photometric aperture radius 𝜌 of 42.4 arcsec, corresponding to projected distances in the sky of 7.2 × 10 4 -1.5 × 10 5 km. Comet C/2012 J1 (Catalina) shows an asymmetric secular light curve, which is typical for comets. The nucleus has a minimum radius of 3.3 km admitting an albedo of 0.04. The inner coma exhibited radial pulsations before perihelion related to the dust rate proxy Af𝜌. The Af𝜌 parameter was inversely proportional to the photometric aperture radius 𝜌 because the angular diameter of the coma was small compared with the aperture radii used. The comet had three outbursts with brightness variations between 0.2 and 2.99 magnitudes per event. The median normalized reflectivity gradient S ′ is 4.4 with an amplitude of 22.9%/100 nm in the spectral range between 440 and 647 nm. The dispersion of the gradient S ′ means that 20% of the measurements are bluer than the solar color.