Central Bureau for Astronomical Telegrams
IAUC 6566: C/1995 O1
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Circular No. 6566
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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COMET C/1995 O1 (HALE-BOPP)
D. C. Lis, M. Gardner, and T. G. Phillips, Caltech
Submillimeter Observatory (CSO); D. Bockelee-Morvan, N. Biver, J.
Crovisier, and P. Colom, Observatoire de Paris; and D. Despois,
Observatoire de Bordeaux, report: "Using the CSO on Feb. 16-20, we
detected the 11(0,11)-10(0,10) 241.7-GHz, 12(0,12)-11(0,11) 263.7-
GHz, and 16(0,16)-15(0,15) 351.6-GHz transitions of HNCO with
integrated line areas on a Tb scale of 0.27 +/- 0.04, 0.18 +/-
0.02, and 0.46 +/- 0.08 K km/s, respectively. The J(24-23) 218.3-
GHz and J(29-28) 263.8-GHz transitions of HCCCN were detected with
line areas of 0.24 +/- 0.03 and 0.19 +/- 0.03 K km/s. The
estimated production rates for HNCO and HCCCN are 2.3 and 0.8 x
10E27 molecules/s, respectively. The HCCCN/HCN abundance ratio is
about 0.06. The J(4-3) lines of HNC at 362.6 GHz and HCN at 354.5
GHz were detected with line areas of 5.8 +/- 0.1 and 18.8 +/- 0.1 K
km/s, respectively, which corresponds to an HNC/HCN relative
abundance of about 0.25; on 1996 Dec. 5, we measured at the CSO a
much lower ratio (0.05), similar to that observed in C/1996 B2
(Irvine et al. 1996, Nature 382, 418). We have also detected the
J(3-2) lines of H13CN at 259.0 GHz and HCN at 265.9 GHz, with line
areas of 0.27 +/- 0.02 and 23.0 +/- 0.08 K km/s, respectively.
This corresponds to an HCN/H13CN abundance ratio of 90 +/- 15. The
first identifications of HNCO and H13CN in a comet were obtained at
the CSO of C/1996 B2 on 1996 Mar. 22-25, (Lis et al. 1997, Icarus,
submitted)."
H. Matthews, Joint Astronomy Centre, Hilo, and Herzberg
Institute of Astrophysics; and D. Jewitt, University of Hawaii,
report submillimeter continuum measurements using the James Clerk
Maxwell Telescope (+ B3 heterodyne SIS mixer receiver with a
continuum backend). Continuum flux densities were measured at 344
GHz within a 14".5 beam; preliminary values on Feb. 9 and 16 UT
were 329 +/- 96 and 464 +/- 62 mJy, respectively. The effective
blackbody cross-section, about 30~000 km**2, is 40 times larger than
in comet 1P/Halley at similar heliocentric distances (e.g., Jewitt
and Luu 1992, Icarus, 100, 187). Comparison with the results by
Kreysa et al. (IAUC 6555) shows that the dust cross-section is
increasing faster than would be expected on the basis of the
decreasing heliocentric distance alone.
Naked-eye m1 estimates: Feb. 18.18 UT, 1.1 (K. Sarneczky,
Szeged, Hungary); 20.20, 1.0 (R. J. Bouma, Groningen, The
Netherlands); 22.49, 0.9 (W. Dillon, Missouri City, TX); 23.47, 0.8
(G. W. Kronk, Troy, IL); 24.42, 0.8 (D. W. E. Green, Lexington, MA).
(C) Copyright 1997 CBAT
1997 February 24 (6566) Daniel W. E. Green
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