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IAUC 6839: 1997 XF11

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                                                  Circular No. 6839
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
BMARSDEN@CFA.HARVARD.EDU or DGREEN@CFA.HARVARD.EDU (science)
URL http://cfa-www.harvard.edu/iau/cbat.html
Phone 617-495-7244/7440/7444 (for emergency use only)


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

1998 TT     R. A. (2000) Decl.     Delta      r    Elong. Phase    V
Mar.  8     6 15.92    +17 56.7    1.557    2.070  106.5   27.4   20.8
     13     6 19.04    +18 08.0    1.629    2.080  102.3   27.8   20.9
     18     6 22.81    +18 18.0    1.701    2.089   98.2   28.1   21.0
     23     6 27.18    +18 26.5    1.773    2.098   94.3   28.3   21.1
     28     6 32.08    +18 33.4    1.846    2.105   90.5   28.3   21.2
Apr.  2     6 37.46    +18 38.7    1.917    2.112   86.8   28.2   21.3
      7     6 43.26    +18 42.1    1.988    2.118   83.3   28.0   21.4

     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.

                      (C) Copyright 1998 CBAT
1998 March 12                  (6839)              Brian G. Marsden

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