Central Bureau for Astronomical Telegrams
IAUC 5480: (5145); N Cyg 1992
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Circular No. 5480
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
Telephone 617-495-7244/7440/7444 (for emergency use only)
TWX 710-320-6842 ASTROGRAM CAM EASYLINK 62794505
MARSDEN or GREEN@CFA.BITNET MARSDEN or GREEN@CFAPS2.SPAN
(5145) 1992 AD
Following the identification of observations of 1992 AD in 1991
and 1989 (IAUC 5462), further images were found on U.K. Schmidt plates
taken in 1982 and 1977, and the object was given the permanent minor
planet number (5145) on MPC 19850. It also appears that the object's
brightness varies essentially by an asteroidal law. J. K. Davies,
Royal Observatory of Edinburgh; and M. V. Sykes, University of
Arizona, report: "JHK photometry of 1992 AD has been obtained using
the U.K. Infrared Telescope with the following results: Mar. 15.399 UT,
J = 14.78 +/- 0.02, H = 14.27 +/- 0.02, K = 14.32 +/- 0.02; 17.281,
14.69 +/- 0.02, 14.31 +/- 0.03, 14.33 +/- 0.03. Assuming V = 17.2
(from the photometry by B. E. A. Mueller and D. J. Tholen on IAUC
5434), this yields reflectivities relative to V of 3.5 (J), 4.0 (H)
and 3.6 (K), which are very consistent with the values for tholins as
reported by Mueller et al. (1992, submitted to Icarus Notes). This
supports the hypothesis that prolonged exposure to galactic cosmic
rays results in tholin formation on the surfaces of Oort cloud comets.
We expect that such an outer layer of complex organics is blown off as
a comet becomes active. New crusts would be formed from the
indigenous refractory material of the object, allowing significant
differences in visual and near-infrared colorimetry, such as that
between (5145) 1992 AD and (2060) Chiron (which may be active all
around its orbit). The former object appears to be inactive, and it
may remain so as it is just past perihelion. However, if it becomes
suddenly active over a significant fraction of its surface, we predict
that its spectrum will change toward that of Chiron and other comets."
NOVA CYGNI 1992
C. E. Woodward, University of Wyoming; and G. F. Lawrence,
University of Minnesota, report the following infrared magnitudes,
obtained using a bolometer on the 0.8-m O'Brien Observatory telescope
on Mar. 15.4 UT: J = 5.51 +/- 0.28, H = 5.44 +/- 0.21, K = 4.47 +/-
0.11, L = 3.47 +/- 0.31.
Selected visual magnitude estimates: Mar. 12.08 UT, 6.3
(A. Boattini, Padua, Italy); 14.11, 6.5 (S. Koushiappas, Nicosia,
Cyprus); 16.12, 6.5 (B. Granslo, Blindern, Norway); 17.13, 6.6
(E. Schweitzer, Strasbourg, France); 18.43, 6.6 (C. Scovil, Stamford,
CT); 19.48, 6.9 (W. Dillon, Missouri City, TX); 20.13, 7.0 (P.
Rapavy, Rimavska Sobota, Czechoslovakia).
1992 March 20 (5480) Brian G. Marsden
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