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THE ASTRONOMER Electronic Circular No 1280      1998 Mar 13 20.10UT
Ed:Guy M Hurst, 16,Westminster Close, Kempshott Rise,  Basingstoke,
Hants, RG22 4PP,England.Telephone/FAX(01256)471074Int:+441256471074
INTERNET: GUY@TAHQ.DEMON.CO.UK             GMH at AST.STAR.RL.AC.UK
WORLD WIDE WEB                    http://www.demon.co.uk/astronomer
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1997 XF11
E. F. Helin, Jet Propulsion Laboratory, reports that K. J. Lawrence
has located prediscovery observations of this object in 1990 on
films taken by Helin, Lawrence and B. Roman in the course of the
Planet-Crossing Asteroid Survey with the 0.46-m Schmidt telescope
at Palomar:

     1990 UT             R.A. (2000) Decl.         B
     Mar. 22.44427   13 15 16.50   -12 54 21.2   17.3
          22.47674   13 15 13.91   -12 54 04.3
          23.44062   13 14 00.86   -12 45 47.4
          23.46632   13 13 58.73   -12 45 34.4

      The following improved orbital elements have been computed by
G. V. Williams, Harvard-Smithsonian Center for Astrophysics, from
99 observations at the 1990 and 1997-1998 apparitions, the mean
residual being 0".58:

                    Epoch = 1997 Dec. 18.0 TT
     T = 1997 July  1.1954 TT         Peri. = 102.4645
     e = 0.483775                     Node  = 214.1319  2000.0
     q = 0.744247 AU                  Incl. =   4.0948
       a =  1.441710 AU    n = 0.5693602    P =   1.731 years

This new computation shows that the encounter with the earth in
2028 will occur on Oct. 26.3 UT, the miss distance then being
0.0064 AU. A computation from the 60-day-arc orbit on MPC 31283
indicated a comparable distance (0.0055 AU).  With regard to the
remarks on IAUC 6837, it should be noted that, from the 88-day arc
of data then available, several independent authorities gave
comparable nominal miss distances for 2028 Oct. 26:
D. K. Yeomans and P. Chodas, Jet Propulsion Laboratory,
                             derived 0.00058 AU;
K. Muinonen, University of Helsinki, 0.00033 AU;
and E. Bowell, Lowell Observatory,   0.00023 AU.
The new computation shows that there were also approaches to
0.032 AU in 1971 and to 0.015 AU in 1957.
IAUC 6839 (extract)

Guy M Hurst