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
Rolando Ligustri
Giovanni Sostero