THE ASTRONOMER Electronic Circular No 587 1991 Dec 16 19.52UT 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 ------------------------------------------------------------------- 1991 VG Using additional astrometric observations made by J. Scotti with the Spacewatch telescope at Kitt Peak on Nov. 26, 27, and 29, and by R. M. West, O. Hainaut, and A. Smette with the 1.5-m Danish telescope at the European Southern Observatory on Dec. 2, D. K. Yeomans, Jet Propulsion Laboratory, provides the following improved orbital elements: Epoch = 1991 Dec. 10.0 ET T = 1992 Jan. 5.8852 ET Peri. = 26.5230 e = 0.074987 Node = 78.9213 1950.0 q = 0.972573 AU Incl. = 1.5906 a = 1.051416 AU n = 0.9142022 P = 1.078 years Perturbations by the earth and by the moon were allowed for separately, and the object's closest approaches to these bodies were 0.0031 and 0.0025 AU on Dec. 5.351 and 6.859 ET, respectively. Similar computations have also been made by J. Chandler, Harvard-Smithsonian Center for Astrophysics, who notes that 1991 VG appears previously to have approached the earth-moon system to a distance of 0.07 AU in early 1975. IAUC 5401 R. M. West reports: "CCD observations were obtained during Dec. 2.12-2.19 UT under very good conditions (seeing 0".7-0".8; long trails of the object were recorded on unguided V- (total 47 min) and B-frames (16 min). The trails are characterized by very rapid variations; due to the high rate of motion the time resolution is about 2 s (during which time the object moved 1"). After careful subtraction of the adjacent sky by interpolation, the lightcurve shows 1.8 mag peak-to-peak variations between V = 16.9 and 18.7; mean V = 17.7 +/- 0.1, mean B = 18.2 +/- 0.2; B-V = 0.5 +/- 0.2, i.e. solar. Although there are differences between the individual trails, we recognize deep minima on all of them, lasting about 20-30 s, interspersed by peaks at maximum brightness of about the same duration; the full 1.8-mag change happens in 15 s. Superimposed on the trails are three flashes at mag 16, each lasting < 2 s; they are quite unlike cosmic-ray events and appear real. It has not been possible to determine the period with certainty, although 7.5 min appears to fit most trail segments. The curve is reminiscent of that of a rapidly rotating satellite, with highly reflective sidepanels. Assuming an albedo of 0.5, the reflecting area is of the order of 30 m**2. These observations therefore support the interpretation of 1991 VG as an artificial object (cf E581), probably rotating around more than one axis." Although the seeing was poor (about 4"), CCD photometry of an image (deliberately trailed in declination) for 7 min on Nov. 29.2 UT by W. Wisniewski with the Steward Observatory's 2.3-m reflector on Kitt Peak seemed to rule out peak-to-peak variations > 0.3 mag with peak widths of more than about 22 s; a series of tracked CCD exposures revealed a rather typical asteroidal variation of amplitude 0.2 mag over a period of about 100 min. Possible space debris candidates for 1991 VG during 1974-1975 (and also around the previous earth encounter in the late 1950s) have been mentioned by J. McDowell, Marshall Space Flight Center, and by R. Rast, Johnson Space Center. Among them are the rockets involved with the Helios A launch in Dec. 1974, the Pioneer 4 launch in Mar. 1959, and various Luna missions. Identification with such space debris requires the action of nongravitational forces (course corrections, fuel leaks, radiation pressure) on 1991 VG; computations by P. Chodas, Jet Propulsion Laboratory, and by B.G. Marsden, Harvard-Smithsonian Center for Astrophysics, confirm these as possibilities, but the situation is far from conclusive.(5402) Guy M Hurst