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- 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