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IAUC 8593: (99942); Poss. N IN SMC

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IAUC number 

                                                  Circular No. 8593
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)
CBAT@CFA.HARVARD.EDU (science)
URL http://cfa-www.harvard.edu/iau/cbat.html  ISSN 0081-0304
Phone 617-495-7440/7244/7444 (for emergency use only)


(99942) APOPHIS
     J. D. Giorgini, L. A. M. Benner, S. J. Ostro, Jet Propulsion
Laboratory; M. C. Nolan, Arecibo Observatory; and M. W. Busch,
California Institute of Technology, report:  "Arecibo (2380-MHz,
12.6-cm) radar observations of (99942) Apophis = 2004 MN_4 (cf.
IAUC 8477) made during Aug. 7.655-7.769 UTC produced a CW detection
and a Doppler measurement of 8186.8 Hz at Aug. 7.713, a correction
of +0.3 +/- 0.2 Hz (+18.9 +/- 12.6 mm/s) relative to nominal
prediction.  Including this Doppler correction in a new orbit
estimate and n-body gravitational propagation increases the 2029
April 13.9 Earth-center miss-distance from 5.77 +/- 0.39 to 5.86
+/- 0.12 Earth radii, reducing the along-track position uncertainty
at closest approach from +/- 1957 to +/- 757 km; the volume of the
spatial uncertainty region decreases from 173000 to 39800 km**3.
The new Doppler measurement increases the predicted nominal Earth
close approach in 2036 from 0.005 to 0.14 AU.  However, we have
found that computational noise intrinsic to 64-bit representations
of real numbers used in arithmetical operations, exacerbated by the
close Earth encounter in 2029, can accumulate trajectory-prediction
error exceeding the radius of the earth by 2036.  Using more
precise 128-bit representations, the specified local error
tolerance was reduced from 10**-14 to 10**-19 and the maximum
predictor/corrector order (used for step-size and error-control
decisions) increased from 14/15 to 21/22. This approach reduces
error growth in the integration due to the finite representation of
real numbers and permits examination of those specific orbit
variations in 2036 for which trajectory offsets comparable to the
size of the earth are significant."


POSSIBLE NOVA IN SMALL MAGELLANIC CLOUD
     J. D. Neill, University of Victoria, and M. C. B. Ashley,
University of New South Wales, report the discovery of an apparent
nova on unfiltered CCD images taken on Aug. 22.463 (at mag 14.5)
and 18.474 UT (mag 14.2) with the 0.45-m ROTSE-III telescope at
Siding Spring Observatory in the course of a nova patrol of the
Small Magellanic Cloud.  The new object is located at R.A. =
1h15m00s.15, Decl. = -73o25'38".1 (equinox 2000.0), which is
approximately 97'.6 east and 35'.9 south of the center of the SMC.
The new object is not present on images by Neill and Ashley from
July 29, 30, 31, and Aug. 1 (limiting mag 17.5) or on a Palomar Sky
Survey plate from 1989 Nov. 20 (limiting red mag about 20.0).

                      (C) Copyright 2005 CBAT
2005 September 2               (8593)            Daniel W. E. Green

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