Central Bureau for Astronomical Telegrams
IAUC 4205: 1986 DA AND 1986 EB; 1982i
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Circular No. 4205
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
TWX 710-320-6842 ASTROGRAM CAM Telephone 617-495-7244/7440/7444
1986 DA AND 1986 EB
E. F. Tedesco, Jet Propulsion Laboratory, California Institute
of Technology; and J. Gradie, Planetary Geophysics Division,
Hawaii Institute of Geophysics, University of Hawaii, report: "10-
and 20-micron observations of 1986 DA and 1986 EB were obtained during
Mar. 12-17 by W. Golisch, J. Gradie, C. Kaminski and E. Tedesco
using the NASA 3-m Infrared Telescope Facility at the Mauna Kea
Observatory. In addition, colorimetry at five wavelengths between
0.36 and 0.85 microns was obtained by R. M. Nelson and E. Tedesco on
Mar. 20 and Apr. 5 at the Kitt Peak National Observatory 1.3-m
telescope. Model albedos derived from the infrared data indicate
moderate albedos for both objects. These albedos, together with
the colorimetric data, establish that both objects belong to the M
taxonomic class, and they are the first of this type to be found
among the near-earth asteroid population. The derived diameters
are 2.0 +/- 0.1 km for 1986 EB and ~ 2.5 km for 1986 DA. The three
nights of thermal infrared data for 1986 EB are well fit by the
standard thermal model, whereas the one night's data for 1986 DA
are not. The infrared data for 1986 DA are fit equally well by a
surface of low thermal emissivity (e.g., bare metal) or by an
extended cloud of micron-sized particles. 1986 DA is well placed
for observation through mid-June (ephemeris on IAUC 4203), and
additional thermal infrared data would be especially valuable in
explaining the anomalous 10-20-micron flux ratio."
PERIODIC COMET HALLEY (1982i)
D. Wickramasinghe, Australian National Observatory; and D.
Allen, Anglo-Australian Observatory, report the discovery during
Mar. 30-Apr. 1 of a variable, broad, emission band centered at 3.4
micron in spectra of the comet's nucleus. The band profile is very
similar to that seen in absorption toward the galactic center and
is likely to arise in the same material. This discovery
underscores the desirability of collecting stratospheric samples to
test for similar infrared behavior and for chemical analysis.
Further naked-eye magnitude estimates by D. W. E. Green (near
Ayers Rock, N.T., Australia): Apr. 12.57 UT, 3.1; 13.57, 3.1;
14.52, 2.9; 15.50, 3.0; the tail length had increased to 6 deg on
Apr. 15. R. Evans, Hazelbrook, N.S.W., notes that the tail was at
least 10 deg long during the total lunar eclipse on April 24.5 UT.
1986 April 24 (4205) Brian G. Marsden
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