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IAUC 7978: C/2002 Q2; V4742 Sgr

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                                                  Circular No. 7978
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
URL http://cfa-www.harvard.edu/iau/cbat.html  ISSN 0081-0304
Phone 617-495-7440/7244/7444 (for emergency use only)

     Further to IAUC 7966, Z. Sekanina writes that he has
calculated an improved set of fragmentation parameters based on 73
differential astrometric observations taken between Aug. 26 and
Sept. 13 (MPC 46490-46491).  The derived separation time of C/2002
Q3 from C/2002 Q2 is 1970.2 (+/- 1.2 yr), when the parent comet was
at a distance of 56 (+/- 1) AU from the sun, the separation
velocity was 0.18 (+/- 0.01) m/s, and C/2002 Q3 (component A) was
subjected to a relative deceleration of 34.8 (+/- 1.3) units of
10**-5 solar gravitational acceleration.  The predicted separation
ephemeris differs very little from that on IAUC 7966.  A
fragmentation sequence for the components of C/2002 Q3 itself has
been determined, based on the astrometry from the period 2002 Sept.
4-14.  It is found that (i) nucleus A, the original, eastern
component, is the primary, (ii) the component labelled C on Sept.
10 and 14 is identical with C on Sept. 4-5, and (iii) the new,
southern condensation from Sept. 10 and 14, called D, is different
from B (the observations attributed to B on MPEC 2002-R54
apparently not referring to what was observed on Sept. 4--5).
[The offsets of B from A on Sept. 4-5 show irreconcilable
discrepancies (in excess of 3") when attempts are made to link them
with the offsets of the C component on Sept. 10 and 14.]  It
appears that C separated from A before 1980, a satisfactory
solution indicating a fragmentation time in 1973 (+/- 4 yr), at
about 52 AU from the sun, a separation velocity of about 0.1 m/s,
and a relative deceleration of about 6 units of 10**-5 solar
gravitational acceleration.  One cannot exclude the possibility
that C separated directly from C/2002 Q2 about the time, or even
before, component A did.  The only satisfactory solution for D
suggests that it broke off from A on 2002 July 5 +/- 2 days (at
about 1.5 AU from the sun) with a relative velocity of 1.3 m/s and
has been subjected to a deceleration of 12 +/- 1 units.  The
predicted offsets of D from A on Sept. 4-5 are -2".4 in R.A. and
-8".9 in Decl.  The history of nucleus B remains unknown.
Predicted separation distances (and position angles) for components
C and D relative to A (0h TT):  2002 Sept. 18, 3".1 (277 deg) and
5".0 (237 deg); 23, 1".5 (245 deg) and 4".7 (292 deg); 28, 1".8
(169 deg) and 7".4 (325 deg); Oct. 3, 3".3 (147 deg) and 10".4 (337
deg); 8, 4".7 (139 deg) and 12".6 (343 deg); 13, 5".7 (134 deg) and
14".1 (346 deg); 18, 6".4 (130 deg) and 15".1 (348 deg); 23, 7".0
(127 deg) and 15".7 (350 deg).

     CCD V magnitudes by J. D. West, Mulvane, KS:  Sept. 22.074 UT,
8.77; 23.064, 9.54; 24.083, 9.22.  Also: Sept. 22.084, B = 9.85.

                      (C) Copyright 2002 CBAT
2002 September 25              (7978)            Daniel W. E. Green

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