New Saturn Satellites
IAU Circular 6243
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Circular No. 6243
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
BMARSDEN@CFA.HARVARD.EDU or DGREEN@CFA.HARVARD.EDU (science)
Phone 617-495-7244/7440/7444 (for emergency use only)
SATELLITES OF SATURN
P. D. Nicholson and C. A. McGhee, Cornell University; M. R.
Showalter and L. Dones, Ames Research Center, NASA; R. G. French,
Wellesley College; S. M. Larson, Lunar and Planetary Laboratory; J.
J. Lissauer, State University of New York, Stony Brook; P. O.
Seitzer, Unversity of Michigan; B. Sicardy, Universite de Paris;
and G. E. Danielson, California Institute of Technology, report:
"During a 12-hr period spanning the Aug. 10 Saturnian ring-plane
crossing, we obtained a total of 48 images with the HST Wide Field
Planetary Camera 2 (+ 890-nm methane-band filter). In addition to
Saturn X (Janus), XI (Epimetheus), and XVII (Pandora), the images
reveal the presence of at least four other objects orbiting in the
vicinity of the F ring. We confirm that S/1995 S 2 lags behind the
predicted position of Saturn XVI (Prometheus) by 19 deg, comparable
to the 21 deg found during the May 22 crossing (IAUC 6192), thus
confirming the probable identification of S/1995 S 2 with
Prometheus (IAUC 6192, 6196), though it appears to be 0.5 mag
fainter than expected. For each of the other three objects we give
below the orbital radius, mean daily motion, longitude at epoch
1995 Aug. 10.5 TT (at Saturn) measured from the ascending node of
Saturn's equator on the J2000.0 earth equator, equivalent radius,
number of observations fitted, and approximate V magnitude at
opposition: S/1995 S 5, 140 060 +/- 400 km, 583.0 +/- 2.5 deg,
130.0 +/- 0.5 deg, 26 km, 15, 17.1; S/1995 S 6, 139 910 +/- 200 km,
584.0 +/- 1.2 deg, 246.0 +/- 0.1 deg, 19 km, 9, 17.8; S/1995 S 7,
139 440 +/- 250 km, 586.9 +/- 1.6 deg, 324.7 +/- 0.3 deg, 18 km,
10, 17.9. These fits assume circular orbits but include the
effects of Saturn's J2 and J4. Maximum residuals are 0".16 (or 1.6
pixels in the Wide Field Camera), corresponding to 1000 km or less.
Radii are calculated from the objects' integrated fluxes, assuming
circular cross-sections and albedos similar to those of Saturn X
and XI. The orbits of S/1995 S 5 and S/1995 S 6 are consistent
with that of the F ring (a = 140 200 km, n = 582.3 deg/day), and we
suspect that these objects are clumps or arcs within this ring
rather than undiscovered satellites, based on their brightness and
the completeness limit of Voyager imaging searches (R about 10 km).
S/1995 S 5 shows appreciable brightness variations with orbital
phase, also suggesting an arc-like structure. The orbit of S/1995
S 7 is indistinguishable from that of Prometheus = S/1995 S 2, with
the new object trailing the latter by 15 deg. The above orbital
radii are substantially different from those of S/1995 S 1 and
S/1995 S 3 (IAUC 6192) and their mean motions too imprecise at
present to permit unambiguous linkage with these objects."
1995 October 4 (6243) Daniel W. E. Green
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