A catalog of observed nuclear magnitudes of Jupiter family comets

A catalog of a sample of 105 Jupiter family (JF) comets (defined as those w ith Tisserand constants T > 2 and orbital periods P < 20 yr) is presented w ith our "best estimates" of their absolute nuclear magnitudes H-N = V(1,0,0 ). The catalog includes all the nuclear magnitudes reported after 1950 unti l August 1998 that appear in the International Comet Quarterly Archive of C ometary Photometric Data, the Minor Planet Center (MPC) data base, IAU Circ ulars, International Comet Quarterly, and a few papers devoted to some part icular comets, together with our own observations. Photometric data previou s to 1990 have mainly been taken from the Comet Light Curve Catalogue (CLIC C) compiled by Kamel (1991). We discuss the reliability of the reported nuc lear magnitudes in relation to the inherent sources of errors and uncertain ties, in particular the coma contamination often present even at large heli ocentric distances. A large fraction of the JF comets of our sample indeed shows various degrees of activity at large heliocentric distances, which is correlated with recent downward jumps in their perihelion distances. The r eliability of coma subtraction methods to compute the nuclear magnitude is also discussed. Most absolute nuclear magnitudes are found in the range 15 - 18, with no magnitudes fainter than H-N <similar to> 19.5. The catalog can be found at: htty://www.fisica.edu.uy/similar to gonzalo/ca talog/.