SOHO/SWAN observations of comets with small perihelia: C/2002 V1 (NEAT), C/2002 X5 (Kudo-Fujikawa), 2006 P1 (McNaught) and 96P/Machholz 1

SWAN, the all-sky hydrogen Lyman-alpha camera on the SOHO spacecraft, designed primarily to image the interplanetary neutral hydrogen around the sun, also observes comets continuously over large portions of their apparitions to the north and south of the ecliptic and at small solar elongation angles. Because of SOHO's location at the L1 Lagrange point, analysis of SWAN images provides excellent temporal coverage of water production. We report here our results of observations of some interesting target comets selected from the extensive SWAN archive. These include three Oort cloud comets C/2002 V1 (NEAT), C/2002 X5 (Kudo-Fujikawa), C/2006 P1 (McNaught) and three apparitions of atypical short-period comet 96P/Machholz 1. The common aspect of these four comets is their small perihelion distances, which are 0.19, 0.09, 0.17, and 0.12 AU, respectively. Their water production rates over their whole apparitions can be approximated by power laws in heliocentric distance (r in AU) as follows: 1.3 x 10 29 r -2.1 s -1 for C/2002 V1 (NEAT), 7.5 x 10 28 r -2.0 s -1 for C/2002 X5 (Kudo-Fujikawa), 5.4 x 10 29 r -2.4 s -1 for C/2006 (P1 McNaught) and 4.6 x 10 27 r -2.1 s -1 for 96P/Machholz 1. We also present daily-average water production rates for the long-period comets over long continuous time periods. We examine these results in light of our growing survey of comets that is yielding some interesting comparisons of water production rate variations with heliocentric distance and taxonomic classes.