92P/Sanguin was discovered by J.G. Sanguin at El Leoncito (Chile) on October 15th 1977 as a 16th magnitude object. Later it was found that the comet had also been registered previously at Mount Palomar on September 13th and at Cerro El Roble (Chile) on October 11th without being recognised.
The comet has a 12.44 year period and makes its third observed perihelion pass in 2002 after the 1977 and 1990 passes. Perihelion at 1.81AU takes place on September 23rd 2002. Despite the fact that it has many relatively close encounters with Jupiter (1864-2126) at between 0.6 and 1.0AU, the orbit is extremely stable as none of the encounters are close enough to make an significant difference to the period or perihelion distance.
92P/Sanguin brightened quickly as it approached perihelion in 2002. This is typical of an evolved object that shows a rapid switch-on of activity on nearing the Sun. Seichii Yoshida has found that the comet brightened as 40 log r pre-perihelion, although the post-perihelion rate of fade was somewhat slower.
The comet’s switch-on and switch-off are so rapid that it is active for less than 5 months pre-perihelion and about 7 months post-perihelion in each orbit.
A few experimental multiaperture observations were taken of the comet using apertures from 10” to 31”. These show that the observed magnitude brightens rapidly in increasing aperture indicating that the coma is highly extended. The calculated values of the coma index are: 18/08/2002, -1.20; 25/09/2002, -1.4; 26/10/2002, -1.2. For a 1/r coma we expect a value of –2.5; the values calculated for 92P/Sanguin are the lowest that we have found for any comet that we have examined so far.
Interestingly though, despite the fact that the coma is much more extended than a 1/r dependence, there is not as large a difference between the values of Afrho calculated in different apertures as one might expect.
92P/Sanguin shows a moderate level of activity, with a value of Afrho of 160-cm at perihelion, although its drops off rapidly with the value of Afrho just 20-cm at T+100 days.
The data shows that dust production drops extremely fast as the comet recedes from the Sun, showing an r-16 dependence. This dependence is far higher than the normal r-5 or r-6 dependence seen in most Jupiter family comets and, again, is indicative of a highly evolved object.
CCD observations in a 10 arcsecond aperture from:
Ramón Naves & Montse Campàs - MPC 213
Rolando Ligustri - MPC 235
Albert Sánchez - MPC 442
Miguel Camarasa - MPC 445
Fabiola Martín-Luis - MPC 954
Carles Pineda - MPC J91
Toni Climent - MPC J97
CCD aperture photometry in apertures of 18.7", 31.2", 0'.6, 1'.0, 1'.3, 1'.4 and 1'.8 from:
Ramón Naves & Montse Campàs