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IAUC 6417: C/1995 O1; 65P

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                                                  Circular No. 6417
Central Bureau for Astronomical Telegrams
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
Phone 617-495-7244/7440/7444 (for emergency use only)

     H. U. Kaufl, European Southern Observatory (ESO), communicates:
"Comet C/1995 O1 was observed on June 5.25 UT with the ESO 3.6-m
telescope (+ TIMMI, a focal reducer for the thermal infrared).
Using the standard N filter (8-13 microns), the comet was clearly
resolved and isophotes could be detected up to a radius of about 5"
from the nucleus.  The images show a strong peak with a FWHM of
2".5-3" within a faint, diffuse cloud that is asymmetrically
extended to the northeast.  Using a photometric aperture of 7" x 7",
the following fluxes have been provisionally derived:  N, 6.85 Jy;
N1 (7.9-8.9 microns), 1.46 Jy; N2 (9.14-10.34 microns), 2.82 Jy; N3
(11.8-13.0 microns), 6.74 Jy.  The photometric results suggest an
infrared dust color temperature of 200 K."
     M. S. Hanner, Jet Propulsion Laboratory, California Institute
of Technology; and T. L. Hayward, Cornell University, report the
detection with the 5-m Hale Telescope (+ SpectroCam-10) of strong
silicate emission in the 8- to 13-micron spectrum of comet C/1995
O1 on June 11.3 UT.  The feature is a factor of 1.8 above a 175-K
continuum and shows an 11.25-micron peak from crystalline olivine
similar to that seen in 1P/Halley.  Nightly images of the inner
coma during June 1-12 reveal a prominent jet extending 5" north of
the nucleus on June 4.5 and 9.5, while the jet was considerably
weaker or absent on all other nights.  On June 4.5, the total flux
in a 10" circle was 5 Jy at 10.3 microns.
     Visual m1 and coma-diameter estimates (cf. IAUC 6408):  May
28.17 UT, 6.8, 10' x 14' (J. M. Trigo, Castellon, Spain, 7x50
binoculars); June 6.44, 6.3, - (D. Seargent, The Entrance, N.S.W.,
10x50 binoculars); 8.37, 6.6, 6'.5 (C. E. Spratt, Victoria, BC,
0.10-m refractor); 10.96, 6.1, 14' (M. V. Zanotta, San Marco Pass,
Italy, 7x42 binoculars); 12.11, 6.3, 14' (R. Lourencon, Jundiai,
Sao Paulo, Brazil, 20x80 binoculars); 12.99, 6.4, 9' (R. J. Bouma,
Groningen, The Netherlands, 7x50 binoculars).

     Total visual magnitude estimates (cf. IAUC 6392):  May 13.28
UT, 12.7 (A. Hale, Cloudcroft, NM, 0.41-m reflector); 19.01, 13.6
(K. Sarneczky, Raktanya, Hungary, 0.44-m reflector); 25.02, 12.3
(J. Carvajal, Teruel, Spain, 0.44-m reflector); June 8.98, 12.0 (K.
Hornoch, Lelekovice, Czech Republic, 0.35-m reflector).

                      (C) Copyright 1996 CBAT
1996 June 13                   (6417)            Daniel W. E. Green

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