Circular No. 3466 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 617-864-5758 PROBABLE OCCULTATION BY 1978 P 1 A. R. Walker, South African Astronomical Observatory, reports the observation, with the University of Cape Town's photometer on the 1-m telescope at Sutherland, of an occultation of the mag ~ 12 star at R.A. = 13h40m45s.1, Decl. = +8o34'48" (equinox 1950.0). The event had a duration of 50s and was centered on Apr. 6d23h39m28s UT. The event was apparently caused by Pluto's probable satellite, 1978 P 1 (cf. IAUC 3464), which is deduced therefore to have a minimum diameter of 1200 km. Positive or negative reports from other observers would be very useful. SATELLITES OF SATURN H. J. Reitsema, Lunar and Planetary Laboratory, reports that observations by P. A. Smith, S. M. Larson and himself with the 1.5-m reflector appear to confirm the objects 1980 S 7 and 1980 S 8, described by Harris and Gibson on IAUC 3463, but there was no obvious detection of 1980 S 9; the approximate separations from the center of Saturn were: 1980 S 7, Mar. 13.35 UT, 17" east and moving in; 1980 S 8, Mar. 15.19, ~ 19" east. Another probable satellite, designated 1980 S 11, was detected some 22" east of Saturn's center on Mar. 14.47 UT, and this object has been confirmed by Harris at Mount Wilson Observatory. With reference to the notes by Laques and Lecacheux on IAUC 3457 and by Lamy and Mauron on IAUC 3463, Reitsema reports the following separations of an object, designated 1980 S 12, detected well to the east of the center of Saturn: Mar. 28.2125 UT, 56".5; 28.2451, 57".9; 28.2692, 59".0; 28.2927, 60".2; 28.3153, 61".7; the object is in the plane of the rings and of mag 17. Further, two of these more distant objects were observed simultaneously on Apr. 8: 1980 S 13, of mag ~ 17.5, moved from 43" west of Saturn on Apr. 8.32 to 41" west on Apr. 8.35; 1980 S 14, of mag 17.3, was located 55" east of Saturn on Apr. 8.15 and attained a greatest eastern elongation of 61" during Apr. 8.26-8.35 UT. STEPANYAN'S STAR Further to the notes on IAUC 3462 and 3465, K. Horne, California Institute of Technology; B. Margon, University of California at Los Angeles; and J. Africano, Sacramento Peak Observatory, write that observations of six further eclipses in 1980 Mar. refine the period to 3h48m08s.3 +/- 0s.5. The epoch remains at HJD 2444293.0243. 1980 April 10 (3466) Brian G. Marsden
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