Central Bureau for Astronomical Telegrams
IAUC 4040: Occn AND TRANSIT PHENOMENA OF PLUTO AND ITS Sat
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Circular No. 4040
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
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
OCCULTATION AND TRANSIT PHENOMENA OF PLUTO AND ITS SATELLITE
R. P. Binzel, University of Texas; E. F. Tedesco, Jet Propulsion
Laboratory; and D. J. Tholen, University of Hawaii, report
detection of the long-awaited occultation and transit phenomena
involving Pluto and 1978 P1 ('Charon'). Tentative observations on
Jan. 16 by Tedesco and B. Buratti appear to have been confirmed on
Feb. 17 by Binzel and on Feb. 20 by Tholen. The Jan. 16 observations
began with the event in progress and consisted of only three
readings at low altitude affected also by instrumental difficulties;
for two hours after the event a flat tracing was obtained
with only 0.004 mag scatter. Conditions for the February observations
were excellent. Observed UT times of minimum, durations in
hours and greatest magnitude changes AB were as follows:
1985 UT phi Duration Delta-B Location and instrument
Jan. 16.467 0.251 (~ 1.0) 0.04 Palomar, 1.5-m reflector
Feb. 17.385 0.248 2.5 0.04 McDonald, 0.9-m reflector
Feb. 20.585 0.750 > 2.0 0.02 Mauna Kea, 2.2-m reflector
The phase phi was calculated from Tholen's formula that gives the
epoch of synodic minimum rotational brightness as JD 2444240.661 +/-
6.38726E; light time is about 0.17 day. The symmetry of the
phases suggests that the eccentricity of the satellite's orbit is
very small. Tholen notes that the phi = 0.25 events refer to
partial transits of the satellite across Pluto and the phi = 0.75
events to partial occultations of the satellite by Pluto, and he
suggests that the difference in depth can possibly be explained by
a higher albedo for Pluto on the western limb. The geometrical
situation is such that the likelihood of further transits and
occultations will decrease as the system approaches opposition,
but observers are urged to monitor possible upcoming events: Feb.
23.77, 26.97, Mar. 2.16 UT, etc. Deeper events, involving also
eclipses and shadow transits, are anticipated by the 1986 morning
quadrature. Detailed study of the whole series of phenomena will
provide extremely important information concerning the orbital and
other physical parameters of the system. Potential observers are
invited to contact the present observers for further information:
addresses are Tholen, Institute for Astronomy, University of
Hawaii, Honolulu, HI 96822; Tedesco, MS-183-501, Jet Propulsion
Laboratory, Pasadena, CA 91109; Binzel, Department of Astronomy,
University of Texas, Austin, TX 78712.
1985 February 22 (4040) Brian G. Marsden
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