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IAUC 6373: C/1996 B2; C/1996 B1

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                                                  Circular No. 6373
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
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)
Phone 617-495-7244/7440/7444 (for emergency use only)


COMET C/1996 B2 (HYAKUTAKE)
     C. Lisse, M. Mumma, and R. Petre, NASA Goddard Space Flight
Center; and K. Dennerl, J. Schmitt, J. Englhauser, and J. Truemper,
Max-Planck-Institut fur Extraterrestrische Physik, Garching, report
the discovery of x-rays from comet C/1996 B2 with ROSAT -- the
first such detections from any comet:  "The observations took place
on nine different occasions during Mar. 26-28 (see IAUC 6350).  The
brightest parts of the comet's x-ray image are diffuse but crescent
shaped, offset sunward by about 6' from the nucleus (projected
distance about 30 000 km), and extend to about +/- 8' (+/- 40 000
km) in the direction perpendicular to the sun-comet direction.  The
observed radiation shows a clear x-ray (rather than ultraviolet)
signature and is strongly time variable on the order of hours.  An
image can be found under
http://www.rosat.mpe-garching.mpg.de/~jer/rda/comet/hyakutake.html.
Preliminary estimates yield peak surface brightness countrates of
about 0.01 count sE-1 arcminE-2, with the comet being at Delta =
0.13 AU.  A probable mechanism for the observed radiation is
scattering of solar x-rays by material in the comet's coma.
Another possibility is that the radiation is derived from energy
deposition by the solar wind."


COMET C/1996 B1 (SZCZEPANSKI)
     Ephemeris extension from orbital elements on MPC 26879:

1996 TT     R. A. (2000) Decl.   Delta     r    Elong. Phase    m1
Mar. 28     9 34.64   - 1 07.5   0.733   1.612  136.6   25.2    8.9
Apr.  2     9 28.26   - 4 55.3   0.806   1.643  130.7   27.5    9.2
      7     9 24.06   - 8 04.5   0.885   1.676  125.4   29.1    9.5
     12     9 21.64   -10 42.6   0.968   1.712  120.6   30.3    9.8
     17     9 20.70   -12 56.4   1.055   1.749  116.3   31.0   10.0
     22     9 21.00   -14 51.0   1.144   1.787  112.4   31.3   10.3
     27     9 22.33   -16 31.0   1.235   1.828  108.8   31.4   10.6
May   2     9 24.53   -17 59.5   1.328   1.869  105.5   31.3   10.8
      7     9 27.45   -19 19.2   1.421   1.911  102.4   31.0   11.1
     12     9 31.00   -20 32.0   1.516   1.955   99.5   30.6   11.3
     17     9 35.08   -21 39.5   1.611   1.999   96.7   30.2   11.5
     22     9 39.64   -22 43.0   1.706   2.045   94.1   29.6   11.8
     27     9 44.60   -23 43.6   1.801   2.091   91.6   29.0   12.0
June  1     9 49.91   -24 41.9   1.897   2.137   89.1   28.3   12.2
      6     9 55.53   -25 38.6   1.992   2.185   86.8   27.6   12.4

                      (C) Copyright 1996 CBAT
1996 April 4                   (6373)            Daniel W. E. Green

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