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 ------------------------------------------------------------------- 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