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THE ASTRONOMER Electronic Circular No 1928      2003 Oct 03 13.33UT
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.theastronomer.org
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COMET C/2001 Q4 (NEAT), COMET C/2002 T7 (LINEAR)
Mark Kidger, Instituto de Astrofísica de Canarias e-mails: "A
comparison of CCD photometry of C/2001 Q4 (NEAT) by Cristavao
Jacques (MPC 859) with photometry of C/2002 T7 (LINEAR) by Ramón
Naves (MPC 213), Julio Castellano (MPC 939) and Joaquín Vidal (MPC
945) at the same heliocentric distance suggests that at present
C/2002 T7 is intrinsically considerably more active
at present, despite nominally having a much fainter absolute
magnitude.

The observations were taken at r=3.51AU (i.e. still in the low
temperature volatile regime), so they reflect distant activity of
the two comets. Values of Afrho in a 10 arcsecond aperture were
455+/-35 cm for C/2001 Q4 (NEAT) and 1040+/-135 cm for C/2002 T7
(LINEAR), suggesting that the latter is approximately twice as
active at present.

An extrapolation of Afrho to perihelion for C/2002 T7 (LINEAR)
assuming that the current trend in activity is maintained after
water vapour sublimation starts at around r=3AU would predict a
value of Afrho at perihelion of approximately 240 000-cm (10
times greater than 1P/Halley). Although it is unlikely that this
rate of evolution will continue it remains a very promising object.

It is of great interest to receive more photometry of C/2001 Q4
(NEAT) from subscribers in the southern hemisphere to compare with
these data. It is important to specify the aperture used and
reduction against USNO A2.0 stars is preferred, as these are
closest to the standard Johnson-Kron-Cousins photometric system."

Editor:
An ephemeris for this comet appeared in the main TA magazine (Vol
40 No 473 p117 [2003]) but is repeated below for convenience:

  Date    R.A. (2000) Dec.     R       r     Elong  Mag.    Motion
          h  m       o  '     (AU)    (AU)     o          "/hr P.A.
2003 Oct 
   3.00   4 39.56  -63 23.2   3.076   3.381   99.0  11.2    61  183
   8.00   4 38.00  -65 25.5   3.034   3.325   98.1  11.1    61  187
  13.00   4 34.95  -67 26.5   2.996   3.268   96.8  11.0    61  191
  18.00   4 30.04  -69 24.7   2.963   3.212   95.3  10.9    60  195
  23.00   4 22.79  -71 18.8   2.932   3.155   93.6  10.8    59  200
  28.00   4 12.62  -73  6.8   2.906   3.097   91.6  10.7    58  206

Naturally the predicted magnitudes are uncertain, hence our appeal
for further observational reports from Southern Hemisphere
observers.

Guy M Hurst