Saturn's F Ring
­ in stellar occultations ­
Nicole Albers
UVIS Team Meeting
Pasadena, Jan 07­09, 2007
> 40 stellar occultations ( July 2004 ­ now )
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> 47 radial cuts at various longitudes, times, and angles
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12 features found are interpreted as temporary clumps
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1 opaque feature as possible moonlet
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Bosh et al. (2002): F ring core orbit model within 100km of F ring core in occultation
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UVIS Team Meeting
Pasadena, Jan 07­09, 2007
Ring width from optical depth:
W =∫ r  dr
Sampled area: ~10km around core
Sampled area: ~500km around core
Width|Peak optical depth
Core feature has the same shape on a scale of about 20km ­ Width appears as simple multiple of optical depth
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Width is not constant with varying optical depth ­ Mass is not conserved in radial cuts ­ Ring material constantly perturbed by external forcing
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Optical depth on average between 0 and 1
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Irrepeatable measurements at various longitudes, times and angles
UVIS Team Meeting
Pasadena, Jan 07­09, 2007
Core feature has the same shape on a scale of about 20km ­ Width appears as simple multiple of optical depth
●
Width is not constant with varying optical depth ­ Mass is not conserved in radial cuts ­ Ring material constantly perturbed by external forcing
●
●
Optical depth on average between 0 and 1
●
Irrepeatable measurements at various longitudes, times and angles
But what about Rider observations?
UVIS Team Meeting
Pasadena, Jan 07­09, 2007
Alp Sco Rev 13 ingress
VIMS
ISS
UVIS
Alp Sco Rev 13 ingress
VIMS
UVIS
Alp Sco Rev 13 ingress
VIMS
UVIS
Alp Sco Rev 13 ingress
VIMS
UVIS
Alp Sco Rev 13 egress
VIMS
UVIS
Summary
F ring appears completely different in every occultation
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Riders are taken simultaneously and sample the same ring area
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Perfect for time variable objects like F ring or observation geometry dependent wakes ●
UVIS Team Meeting
Pasadena, Jan 07­09, 2007