Central Bureau for Astronomical Telegrams
IAUC 6388: C/1996 B2
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Circular No. 6388
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
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)
BMARSDEN@CFA.HARVARD.EDU or DGREEN@CFA.HARVARD.EDU (science)
Phone 617-495-7244/7440/7444 (for emergency use only)
COMET C/1996 B2 (HYAKUTAKE)
D. Despois, Observatoire de Bordeaux; J. Wink, R. Neri, R.
Lucas, M. Grewing, S. Guilloteau, and A. Dutrey, Institut de
Radioastronomie Millimetrique (IRAM), Grenoble; and P. Colom, D.
Bockelee-Morvan, E. Gerard, H. Rauer, N. Biver and J. Crovisier,
Observatoire de Paris-Meudon, report: "We have clearly detected the
two main hyperfine components, and marginally seen the third, of
the HCN (1-0) transition at 88.6 GHz in comet C/1996 B2 on Mar.
23.1 UT at the IRAM Plateau de Bure Interferometer (four 15-m
antennas). The synthesized beam was 3".8 x 2".4 (baseline range
50-200 m). The emission source is compact (3" apparent size from a
Gaussian fit) and located within about 1" of the predicted optical
ephemeris position. Averaging the data circularly around the
fitted position, the velocity-integrated visibility (fringe
amplitude counted in flux density units) decreases from 0.39 +/-
0.05 to 0.08 +/- 0.07 Jy km/s for baselines 75 to 165 m, averaged
in a channel 1 km/s wide that is centered on the main hyperfine
component. This is much less than the corresponding velocity-
integrated single-dish flux density of 4 +/- 0.1 Jy km/s in the 55"
primary beam; the ratio seems to agree with optically-thin parent-
molecule emission. The same line was again imaged on Mar. 29.6
(visibility-integrated over the central channel 1 km/s wide),
yielding 0.75 +/- 0.11 Jy km/s with an antenna baseline separation
of 15 m, 0.19 +/- 0.05 at 45 m, 0.21 +/- 0.07 at 75 m, and 0.08 +/-
0.04 at 165 m; the single-dish flux integrated over the same
channel was 2.5 Jy km/s. The CO (2-1) line at 230 GHz was observed
at the same time, with a synthesized beam of 1".5, yielding 3.7 +/-
0.4 Jy km/s with an antenna baseline separation of 15 m, 1.22 +/-
0.2 at 45 m, 0.59 +/- 0.18 at 75 m, and 0.25 +/- 0.13 at 165 m; the
single-dish flux (22" primary beam) was 20 Jy km/s. For both
molecules, the peak of the velocity-integrated emission is
displaced by about 3" from the computed nucleus position for Mar.
29. On both days and for both molecules, the emission peak in
individual channel maps seems to shift with velocity, which may be
due to jet emission."
Total visual magnitude estimates: Apr. 18.80 UT, 2.4 (V.
Znojil, Brno, Czech Republic, naked eye); 19.81, 1.4 (K. Sarneczky,
Raktanya, Hungary, naked eye; 65 deg tail in p.a. 40 deg); 20.14,
1.5 (R. Keen, Mt. Thorodin, CO, naked eye; 96 deg tail in p.a. 31
deg); 21.82, 1.9 (M. V. Zanotta, Milan, Italy, 7x42 binoculars);
22.86, 2.8 (A. Pereira, Cabo da Roca, Portugal, naked eye); 23.80,
1.8 (M. L. Paradowski, Lublin, Poland, 7x35 binoculars); 25.18, 1.8
(C. E. Spratt, Victoria, BC, 11x80 binoculars).
(C) Copyright 1996 CBAT
1996 April 26 (6388) Daniel W. E. Green
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