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IAUC 4158: PLUTO; 1985p

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                                                  Circular No. 4158
Central Bureau for Astronomical Telegrams
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
TWX 710-320-6842 ASTROGRAM CAM    Telephone 617-495-7244/7440/7444

     D. J. Tholen, Institute for Astronomy, University of Hawaii,
reports: "Successful observations of the 1985 Dec. 14 partial
transit of Charon (Pluto I) across Pluto were obtained with the
2.24-m telescope on Mauna Kea.  The rise from minimum light was
steeper than expected (~ 0.10  mag/hr), possibly due to a region
of darker material on the southwestern portion of the projected
disk of the planet; such a region would also explain the asymmetry
seen in the 1985 Feb. 17 event (Binzel et al. 1985, Science 228,
1193) and is consistent with a surface albedo distribution that
can reproduce the planet's overall lightcurve.  Improved values
for the magnitude and color of the primary comparison star for
1986 (Tholen 1985, A.J. 90, 2353) were also obtained: B = 13.119,
B-V = +0.741 (uncertainties < 0.010 mag).  No correction to the
predicted times of the events in 1986 is apparent at this time."

     S. M. Larson, Lunar and Planetary Laboratory, University of
Arizona, reports that CCD images obtained by D. Levy and himself
with 1.5-m and 0.5-m telescopes on 1985 Dec. 16.3, 17.4, 18.3 and
22.3 UT show a detached dust tail extending over 20" to the north-
east of the nucleus and curving in the direction of increasing
position angle.  The distance of the point of maximum intensity in
the tail was about 6" from the nucleus on the first three nights,
but the position angle slowly decreased.  Spectra obtained on Dec.
18 over the range 380-760 nm show only continuum.

     A. R. Klemola, Lick Observatory, writes that an exposure with
the Crossley reflector on 1985 Dec. 17.3 UT shows a sharp stellar
object separated by an almost clear gap from a diffuse coma or
tail feature.  The center of the diffuse feature was 5"6 to the
northeast of the stellar object.  There is an indication of the
same phenomenon on Nov. 13.3 and 14.3; the separation was then 3".

     Revising the estimate of tail length given on IAUC 4136, W.
Landgraf telexes that the Mainz observation on Nov. 15.1 UT shows
an apparent jet, leaving the comet in p.a. 75, curving after 7"
to p.a. 58, after 5" more to p.a 80 and ending after another 5".

     Visual magnitude estimate by J.-C. Merlin, Le Creusot, France
(0.40-m reflector): 1985 Dec. 12.81 UT, 12.5.

1986 January 3                 (4158)              Brian G. Marsden

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