Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005dps....37.6205n&link_type=abstract
American Astronomical Society, DPS meeting #37, #62.05; Bulletin of the American Astronomical Society, Vol. 37, p.763
Astronomy and Astrophysics
Astronomy
2
Scientific paper
On May 24 and June 11, 2005 the Cassini Visual and Infrared Mapping Spectrometer (VIMS) observed grazing occultations of the long-period variable star, o Ceti (spectral type M7 III, mK = -2.60). The first occultation track penetrated the rings to a minimum radius of 115,000 km, providing 2 complete profiles of the F and A rings as well as the Cassini Division, while the second track penetrated to a radius of 126,000 km, in the inner A ring. The sampling interval was 80 ms, but the radial resolution is limited by the projected stellar diameter which ranges from 0.25 -- 2.7 km, depending on ring longitude. Due to the very small ring inclination to the line of sight of 3.45o, the B ring and much of the A ring appear almost opaque, while extremely high S/N ratio lightcurves were obtained of low optical depth regions such as the F ring and Cassini Division. All four cuts across the eccentric F ring reveal a dense central strand of FWHM 25 -- 45 km flanked by inner and outer strands which are variable both in normal optical depth (0.005<τ <0.035) and radial separation (250 -- 465 km). All three strands are embedded in a broad `skirt' which is at least 1200 km wide. Within the 325-km wide Encke Gap in the outer A ring are three quasi-circular narrow ringlets, as seen in Cassini images (Porco et al., 2005), with variable optical depths in the range 0.001<τ <0.007. In the Cassini Division, density waves associated with the weak Atlas 5:4 and Janus 7:5 resonances (ILRs) are clearly seen, with the former providing an estimate of the surface mass density of 1.4±0.2 g/cm2, identical to that obtained by Porco et al. (2005). Systematic variations in the transmission of the A ring with longitude are qualitatively consistent with gravitational wake models of Salo et al. (2004). This work was supported by NASA under a contract with the Cassini-Huygens Project.
Cassini Vims Team
Hedman Matthew M.
Nicholson Philip D.
Wallis B.
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