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IAUC 3051: Occn OF SAO 158687 BY URANIAN Sat BELT; CSVS 6997

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                                                  Circular No. 3051
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

     J. L. Elliot, E. Dunham and D. Mink, Cornell University, report
that their observations from the Kuiper Airborne Observatory
show a group of five secondary occultations of SAO 158687 both before
and after the star was occulted by Uranus on Mar. 10 (cf. IAUC
3048).  They note that the times of the individual secondary
occultations are remarkably symmetrical with respect to the occultation
by Uranus itself and suggest that the occulting material is therefore
confined to specific narrow rings in the 7000-km-wide belt.
The events, labeled with Greek letters in order of increasing
separation from Uranus, were recorded as follows, where the UT times
correspond to the middle of each occultation, and the subscripts 1
and 2 refer to the different (mean) locations of the Airborne
Observatory (the altitude of which was 12.5 km), namely, 1: Long. =
-82o11', Lat. = -50o20'; 2: Long. = -101o19', Lat. = -50o21'.

     Event        UT     Duration   Event        UT     Duration
     alpha1    20h20m55s    1s      alpha2    21h45m52s    1s
     beta1     20 19 34     1       beta2     21 47 06     1
     gamma1    20 16 58     1       gamma2    21 49 45     1
     delta1    20 16 03     1       delta2    21 50 39     1
     epsilon1  20 11 46     7       epsilon2  21 54 06     4

     R. L. Millis, Lowell Observatory, reports that five occultation
events were also detected by P. Birch, D. Trout and himself
with the 61-cm reflector at the Perth Observatory (cf. IAUC 3048).
Mid-times of these events (denoted with subscript 3) are:

     Event        UT     Duration   Event        UT     Duration
     alpha3    20h23m43s    1s      delta3    20h15m59s    1s
     beta3     20 23 19     1       epsilon3  20 10 33     8
     gamma3    20 18 44    1-2

     M. W. Feast, South African Astronomical Observatory, reports
that J. Churms monitored the occultation at Cape Town (subscript 4)
and (after learning of the times observed by Elliot et al.) provided
the following mid-times for some short-duration events:

     Event        UT     Duration   Event        UT     Duration
     alpha4    21h55m20s    -       delta4    22h00m13s    _
     beta4     21 56 38     -       epsilon4  22 03 44     6s
     gamma4    21 59 18     -       zeta4     22 07 11     8

These first four events were the only ones of significance (dips of
~ 1 mm on the photometer trace) observed between 21h45m and 22h02m
UT.  Observations began at 20h40m, but the trace was less steady
during the early stages because of low altitude.  The epsilon4 event was
a major one (amounting to ~ 1 cm on the trace, about as much as the
Uranus occultation itself), and the trace was noticeably ragged
(dips ~ 1 mm) between 22h02m and 22h05m.  The zeta4 occultation had a
depth of 3 mm but occurred at the very end of the trace.  Feast
remarks that the photometer was a conventional (not a high speed) one
and that the dips of short duration will not be faithfully reproduced
as to their shape.

     A letter received from M. K. V. Bappu, Indian Institute of
Astrophysics, gives the time of the beginning of the occultation
observed at Kavalur as 20h19m51s UT (rather than 20h19m15s; cf. IAUC
3048), from which we can define for the middle of the event:

     Event        UT     Duration
     epsilon5  20h19m55s    9s

     The values correlated below for the distances of the occulting
material from the center of Uranus (in km, and projected on the
plane of Uranus' equator) were derived by the undersigned.  The
relative positions of Uranus and the star were adjusted so that the
distances for the first four events with subscripts 1 and 2 coincide
(the mutual agreement among them being +/- 40 km) and so that
the distance for epsilon5 is the mean of those for epsilon1 and 2 (i.e. 51 700
km).  Coincidence of the distances for epsilon5 and 1 produces an
increase of ~ 600-700 km in the distances of the rings.

     Event     Distance     Event     Distance     Event     Distance
                            alpha3     42 200
                            beta3      42 500
     alpha1,2   44 900                             alpha4     45 000
     beta1,2    45 900      gamma3     45 700      beta4      46 000
     gamma1,2   47 900      delta3     47 800      gamma4     48 000
     delta1,2   48 600                             delta4     48 800
     epsilon1   52 000      epsilon3   51 900
     epsilon2   51 400                             epsilon4   51 600
                                                   epsilon5   54 300

     Dr. Elliot is planning to make a detailed study of these
occultations and would appreciate receiving observations (including
photometer tracings).  His address is: Center for Radiophysics and
Space Research, Cornell University, Ithaca, NY 14853, U.S.A.

CSVS 6997
     B. V. Kukarkin and N. E. Kurochkin, Sternberg Astronomical
Institute, propose CSVS 6997 (R.A. = 13h05m57s, Decl. = +32o52'.8, equinox
1900.0) as the counterpart for the radio source OP 313.  Moscow
plates show an outburst to mpg ~ 16 in 1958; at minimum mpg ~ 19.

1977 March 21                  (3051)              Brian G. Marsden

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