Circular No. 5402 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 1991 VG Further to IAUC 5401, R. M. West also reports: "CCD observa- tions were obtained during Dec. 2.12-2.19 UT under very good condi- tions (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 mo- tion the time resolution is about 2 s (during which time the object moved 1"). After careful subtraction of the adjacent sky by inter- polation, the lightcurve shows 1.8 mag peak-to-peak variations be- tween 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 hap- pens 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 re- flecting area is of the order of 30 m**2. These observations there- fore support the interpretation of 1991 VG as an artificial object (cf. IAUC 5387), probably rotating around more than one axis." Al- though 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; experiment- al 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. 1991 December 13 Daniel W. E. Green