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IAUC 3048: Occn OF SAO 158687 BY URANUS AND Sat BELT

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                                                  Circular No. 3048
Central Bureau for Astronomical Telegrams
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
Cable Address: SATELLITES, NEWYORK     Telex: 921428
Telephone: (617) 864-5758

     Amplifying the brief announcement on IAUC 3047, J. L. Elliot
reports that several secondary occultations of SAO 158687 on Mar.
10 were observed by E. Dunham, D. Mink and himself from the Kuiper
Airborne Observatory and also by R. L. Millis, P. Birch and D.
Trout at the Perth Observatory.  Both groups independently concluded
that these occultations were caused by bodies that are apparently
part of a satellite belt about 40 000 km distant from the center
of Uranus.  The diameters of the satellites range from 100 km
to much smaller values.  The occultation by Uranus itself was
successfully observed from the Airborne Observatory (located at Long. =
-90o, Lat. = -50o) and lasted ~ 25 min centered on 21h06m UT.  The
Uranus occultation did not occur at the Perth Observatory.  The
secondary occultations took place during an 8-9 min interval around
20h16m UT and during a similar interval around 21h50m UT (although
dawn prevented observations of the latter events in Perth).

     M. K. V. Bappu, Indian Institute of Astrophysics, cables:
"Using the 102-cm reflector at Kavalur (Long. = -5h15m19s.6, Lat. =
+12o34'32"), Bhattacharyya and Kuppuswamy found the diminution of
SAO 158687 during the occultation by the atmosphere of Uranus to be
0.046 magnitude at an effective wavelength of 7500 A.  Visually and
photoelectrically they observed the complete disappearance of the
star for 8s.9 beginning at 20h19m15s UT and ascribe this to
obscuration by a hitherto unknown satellite of the planet."

     Computations by the undersigned show that the asymmetry in the
times of the satellite occultations about the main occultation (as
observed at the Airborne Observatory) is consistent with the existence
of a circular belt in the plane of Uranus' equator.  Allowance
for foreshortening yields the radii of the inner and outer edges of
the belt as 44 000 and 51 000 km, respectively.  The Kavalur observation
suggests occultation by a 100-km-sized body near the outer
edge of the belt.  Other observers are urged to examine their
records for further evidence of this belt.  At Sutherland, times of
mid-occultation by the belt would have been 20h22m and 21h59m UT;
at Mauritius, 20h23m and 21h54m; at Lembang, 20h20m and 21h46m; at
Kyoto, 20h22m; at Helwan, 21h56m.  Those wishing to attempt to
detect the satellite belt directly are advised that at the present
opposition it should be located from 3".5 to 4".0 to the north and
south of the center of Uranus and from 2".7 to 3".1 to the east and
west; the brightest bodies in it are expected to have mv ~ 19.

1977 March 14                  (3048)              Brian G. Marsden

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