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IAUC 4867: NEPTUNE; JUPITER

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                                                Circular No. 4867
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
Telephone 617-495-7244/7440/7444 (for emergency use only)
TWX 710-320-6842 ASTROGRAM CAM     EASYLINK 62794505
MARSDEN or GREEN@CFA.BITNET    MARSDEN or GREEN@CFAPS2.SPAN


NEPTUNE
     Further to IAUC 4806 and 4824, the Voyager Imaging Team reports
the discovery of two more satellites, 1989 N5 and 1989 N6, in Voyager
2 narrow-angle imaging data.  Each was observed in at least 25 frames
over a time span of 11 days, during which the measurement error was
about 150 km per narrow-angle pixel or smaller.  The root-mean-square
post-fit residuals are of the order of a single narrow-angle camera
pixel.  The orbits are direct, and that of 1989 N5 appears to be
nearly circular and equatorial.  The orbit of 1989 N6 is circular but
has an inclination of about 4.5 deg.  The revolution periods are 0.31
and 0.29 days, and the mean radial distances are about 50 000 km and
48 200 km, respectively.  Preliminary calculations indicate that 1989
N5 is about one visual magnitude fainter than 1989 N3 in the Voyager 2
narrow-angle clear filter and that 1989 N6 is two magnitudes fainter
than 1989 N3.  Estimated diameters for the satellites 1989 N1-1989 N6
are thus 420, 200, 140, 160, 90, and 50 km, respectively.
     It also appears that the ring arcs mentioned on IAUC 4830 are in
fact complete rings, although the outer ring contains prominent
arclike sections.  The rings have radial distances of 62 900 and
52 300 km, and the earlier designations are to be replaced by 1989 N1R
and 1989 N2R.  The Voyager Imaging Team also reports a broader ring,
1989 N3R, some 1500-2000 km wide and centered at 41 900 km from
Neptune's center.  The designation 1989 N4R is given to diffuse sheet,
extending all the way inward from a distance of about 57 500 km, while
1989 N5R refers to a relatively narrow feature at the outer edge of
this sheet.
     It is now virtually certain that the satellite 1989 N2 is
identical with 1981 N1 (cf. IAUC 3608), despite an earlier suggested
categorization of 1981 N1 as a ring arc (cf. IAUC 4022), rather than
as a satellite.  It appears probable, however, that 1984 N1 (cf. IAUC
3962, 3968) is associated with one of the arclike structures in
the ring 1989 N1R.


JUPITER
Revision to IAUC 4863.  M. Ressler and M. Shure (University of Hawaii)
observed Jupiter on 1989 Aug. 4.  IRTF staff observers included W.
Golish, D. Griep, and C. Kaminski.


1989 September 29              (4867)             Daniel W. E. Green

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