Wednesday, March 26, 2008

Comet 7P/Pons-Winnecke

Comet 7P/Pons-Winnecke is currently approaching the Sun, during its journey to the inner Solar System. On 2008, March 25.9 we imaged it from the Remanzacco Observatory (Italy): after weeks of bad weather, a storm finally cleared up the sky, so we were able to perform some follow-up of this faint comet, while it was slowing moving in Ursa Major.

In our stacking (average of 20 unfiltered exposures, 120 seconds each, through a 0.45-m f/4.4 reflector + CCD) the comet appears starlike (no coma or tail are visible; same FWHM of the field stars):

We performed a preliminary photometric analysis, that returned a magnitude of R~ 19.5; at this low level of activity, the afrho parameter (proxy of the dust abundance within the coma) is dominated by sunlight scattered by the nucleus, so it doesn't have a straightforward interpretation (just for the record, its current value is close to a few cm).

7P/Pons-Winnecke belongs to the Jupiter family cometary class (q~ 1.2 AU, Q~ 5.6 AU, i~ 22 deg, period~ 6.4 years). During its current approach, it has been recovered at magn.21 on 2007, Dec. 17 by K. Sarneczky (University of Szeged), 0.60-m Schmidt + CCD. It will reach perihelion at the end of September 2008, and it's not supposed to get any brighter than magnitude 12.5 at its best (but at small solar elongation).

C. Snodgrass et Al. [A&A 444, 287-295 (2005)] estimated the nucleus radius at ~2.2 Km, and bracketed its rotation period between 6.8 and 9.5 hours.

This comet has been related to the June Bootids meteor stream, that was pretty active during some of the comet's passages in the first quarter of the past century. However the current activity of this meteor shower is rather modest, probably because the gravitation influence of Jupiter changed significantly the orbital path of the comet and its associated meteoroid debris.

Giovanni Sostero & Ernesto Guido

No comments: