CCD photometry of distant comets

While it is apparent that many comets are active beyond the canonical distance of 3 AU, few surveys of cometary activity have been performed in this region previously. Such a survey enables a more accurate determination of the proportion of comets that exhibit little or no outgassing at these distances. Results are presented of CCD observations of comets in the region of 3 AU ≤ Rh ≤ 6 AU obtained with the 1m JKT on La Palma. Photometric observations of 15 comets were obtained, 7 of which displayed coma activity and 8 of which appeared inactive. BVR photometry was performed on these comets to determine dimensions, colours and outgassing rates. Although 40P/Vaisala 1 and 26P/Grigg-Skjellerup were not detected, upper limits to their nuclear radii are presented. The results obtained are compared with previous observations.