Presentiamo qui uno dei report inviati periodicamente dal GAT al Central Bureau for Astronomical Telegrams, INTERNATIONAL ASTRONOMICAL UNION. Per questo motivo il testo in Inglese.

C/Hale-Bopp (1995 O1) observations.

from May 21 to September 15, 1996 : 0,335m reflector (f/4.8)
November 23.8 and 24.8, 1996 : 0.15 m reflector ( f/5)
CCD camera with pixels of 9 microns, without filter (spectral sensitivity: 0.8-1.1 microns).

Observations performed during 6 months, from May 21 to November 24 1996, confirmed a regular increase of the C/Hale-Bopp cometary activity. As a principal indication of this activity, we observed an increase of the number and of the intensity of some spectacular jets coming from the nuclear region . In particular we observed : 3 jets from May 21 to June 6, 4 jets from July 25 to August 4, 5 jets on August 4 and 8, 6 jets on August 16, 7 jets from September 11 and 15, 8 jets on November 24.

After elaboration of our CCD pictures with the Larson-Sekanina algoritm and a ring masking process, we derived these position angles (p.a.) : p.a.=65 for the principal jet (antisolar direction), p.a.=25 and 95 for the other two more important jets (in lengh and brightness), p.a.= 110-165-220-280 -350 for other fainter and shorter jets.

The jet at p.a.=165 appears to be broad and spread apart and it could be produced by the perspective overlapping of two more collimated jets. This interpretation is linked to the observation that all other jets seem very narrow and collimated up to 1.5' from the nuclear region. The complete analysis of all our observations demostrates that jets DON'T SHOW ANY INTRINSIC ROTATION, the only rotation being linked to the change of the Earth-Comet-Sun position angle.

Nickname of 'porcuspine comet' is, again, the best representation of this extraordinary comet.

December 1, 1996

F.Manzini, R.Crippa and C.Guaita
Member of a Consortium created by Prof. C.Cosmovici to coordinate Italian studies about recent big comets.

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