THE ASTRONOMER Electronic Circular No 622     1992 March 31 19.44UT
Ed:Guy M Hurst, 16,Westminster Close, Kempshott Rise,  Basingstoke,
Hants, RG22 4PP,England. Telephone/FAX(0256)471074 Int:+44256471074
Telex: 9312111261 Answerback: TA G                     JANET BOXES:
GMH at UK.AC.CAM.ASTRONOMY.STARLINK or GUYH at UK.AC.SUSSEX.CLUSTER
TELECOM GOLD: 10074:MIK2885                       PRESTEL 256471074
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EY CYGNI
Patrick Schmeer, Bischmisheim, Germany has reported a rare outburst
of the dwarf nova EY Cygni (RA 19h 52m 41s DEC +32 13.7',1950). In
response to our alert, confirmation has been obtained by Norwegian
observers:
1992 Mar 19.169UT,   [13.2 (P.Schmeer)
         28.148UT,    11.0 (Schmeer)
         28.162UT,    11.0 (Schmeer)
         29.02UT,     11.6 (O.Midtskogen, Tranby, Norway)
         30.05UT,     11.4 (B.Granslo, Fjellhamar, Norway)
The previous observed outburst was on 1986 August 29 at mag 11.0v
(IAUC 4249, 4252, 4258)

(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."
IAUC 5480

SW URSAE MAJORIS
Patrick Schmeer, Germany, reports further magnitudes of the current
outburst (cf E620):
Mar 18.935UT, [12.5; 21.787, 11.0; 23.856, 11.2; 27.007, 11.7.
He comments that the previous outburst occurred in 1991 March
(cf IAUC 5199, 5206) and that the current event is a faint
supermaximum.

Guy M Hurst