Pic du Midi Images of Comet 1996 B2 Hyakutake

Observers: Laurent Jorda, Jean Lecacheux
Location: Pic du Midi Observatory, France
Date: March 18-19, 1996

First detection of the nuclear rotation

These six images are taken with a HiSis 44 camera build with a Kodak KAF 1600 CCD device on March 19th. We used the 105 cm telescope at Pic du Midi Observatory at Nasmyth-Cassegrain focus (F/17) with a large pass band filter center at 700 nm (fwhm = 400 nm). As we used 30% of the comet light to guide directly on the nucleus, the time exposure of each picture could reach 300 seconds without any guiding defects. The seeing was good (0.9 arcsec) for these 5 minutes exposures, but more important is the fact that we observed during a 6 hours run. North is up and west is on the right. We have substracted a radial profile from each image to enhance the asymmetric details. The ion tail is clearly visible at PA = 275 deg. Two curved jets are present on most of the frames.

This long observation run allow us to give the first explanation of the moving jet observed at ESO 3.5m NTT and at Pic du Midi on february 10th. Two jets are visible on most of the frames. It is clear that the activity begins at morning limb near PA 200 deg, is maximum at noon near PA 95 deg, and disappears at evening limb near PA 350 deg. The rotation period seems to have a range of 5 to 9 hours, it is probably 6.1 hours if we use the ESO NTT images and some previous observations at Pic du Midi. We suggest also that the nucleus shows actually its southern hemisphere to Earth-based observers and that Sun lies near its equatorial plane.

Observers : Laurent Jorda, Jean Lecacheux

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