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IAUC 3811: 1983d

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                                                  Circular No. 3811
Central Bureau for Astronomical Telegrams
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
TWX 710-320-6842 ASTROGRAM CAM     Telephone 617-864-5758

     S. M. Larson, Lunar and Planetary Laboratory, communicates
the following observations by J. R. Johnson and himself with the
1.5-m reflector at the Catalina Station: "(1) Direct visual
inspection (at up to 1000 x) of the comet's nuclear condensation
on May 11.2 UT showed a 0.5 +/- 0.1 disk that, unlike nearby star
images of the same brightness, appeared to have a sharp edge and
uniform brightness.  This 12-km feature was presumably not the
nucleus, since there was no indication of phase (and the phase
angle was 96deg).  The nuclear condensation was estimated to be of
mag 10.5 +/- 0.5, implying an albedo of 0.0085.  (2) Direct images
of the inner coma on May 11 show a sunward-directed fan indicative
of a slowly-rotating nucleus.  An extremely faint extension 300 km
in the antisolar direction also showed a reflection spectrum.  (3)
Spectra in the range 300-560 nm obtained on May 6, 7 and 11 show
emission lines of OH,  NH,  CN,  C2,  C3,  NH2,  CO+,  C02+.  There
are also lines consistent with S2 (cf. IAUC 3809).  The emissions,
including those of the ions, were brighter on the sunward side."

     D. Campbell, P. Ford, A. Forni, J. Harmon, A. Hine, B. G.
Marsden and I. I. Shapiro, Arecibo Ionospheric Observatory,
Massachusetts Institute of Technology and Harvard-Smithsonian Center
for Astrophysics, report that continuous-wave radar observations
at 2380 MHz at Arecibo during a 2-hr interval on May 11.9 UT
yielded good strong returns (with a 4-Hz bandwidth) and a suggestion
of a weaker and wider 'skirt'.  These observations would not
have been possible if it were not for the magnificent response to
the pleas for accurate astrometry (IAUC 3798, 3801, 3804, 3808).

     With reference to the suggestion (IAUC 3801) that meteors
might be detected from the comet, P. M. Millman, Herzberg Institute
of Astrophysics, reports that preliminary analysis by A. F.
Cook and himself of meteor radio data in Ottawa shows no evidence
of unusual meteor activity: lowpower data were obtained over a 72-
hr interval centered on May 10.08 UT, highpower data over 24 hr.
Visual and photographic monitoring by S. Clifton at Marshall Space
Flight Center during May 10.0-10.4 also gave negative results.

     Further visual estimates of total magnitude and coma diameer:
May 10.08 UT, 2.9, 98' (J. E. Bortle, Stormville, NY (0.05-m
refractor); 10.17, 2.9, 129' (C. S. Morris, Harvard, MA, naked
eye); 11.18, 2.3, 193' (Morris); 12.08, 1.8, 2 deg (Bortle);
12.27, 1.7, 180' (Morris); 13.07, 3.1, 1 deg (Bortle).

1983 May 18                    (3811)              Brian G. Marsden

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