HSP observations of the F ring and the B ring edge
Nicole Albers
UVIS Team Meeting, 5th ­ 7th January 2010, Boulder F ring observations: HSP [2005­2009]
4 additional occs since last meeting giving a total of 116 F ring occs
● 10 low­B observations (though mostly low signal to noise ratio)
● Supplementary core: 19 obvious occurrences
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2
Nicole Albers
UVIS Team Meeting, Boulder, January 2010
F ring core orbit model – comparing the new data
2008­332T
Initial data cutoff
3
Nicole Albers
UVIS Team Meeting, Boulder, January 2010
Evidence for a discontinous F ring core
2008­332T
Initial data cutoff
4
Nicole Albers
UVIS Team Meeting, Boulder, January 2010
Del Per R36
The Hya R94 egress
The Hya R104 egress
5
Nicole Albers
UVIS Team Meeting, Boulder, January 2010
F ring component detections
Strand activity has been constantly increasing, consistent with the registered F ring core residual trend
● 80% of multiple inner strands occurred after the F­ii appeared
● 40% of F­ii have a larger optical depth than the F ring core
● 3 known core misidentifications (good indications for yet more, without necessarily having large residuals)
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6
Nicole Albers
UVIS Team Meeting, Boulder, January 2010
F ring: Work in progress
F ring strands:
F ring strands: HSP observations at this point don't seem to show the kinematic spiral seen by ISS
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Key to strand kinematics is to figure out the kinematics of F­ii ●
Essential to “sort” potential multiple detections ●
Find potential “strand­core­crossing” points (core structure)
7
Nicole Albers
UVIS Team Meeting, Boulder, January 2010
B ring edge: HSP observations [2004 ­2009] ●
Nicole Albers
Total of 103 occultations, some of them opaque 8
UVIS Team Meeting, Boulder, January 2010
Evidence for streamline compression at the edge
Optical depth is largest when edge is most compressed, most radially inward, in pericenter of dominant m=2 pattern
● But the optical depth has been increasing in time since 2004
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9
Nicole Albers
UVIS Team Meeting, Boulder, January 2010
Optical depth at the edge 10
Nicole Albers
UVIS Team Meeting, Boulder, January 2010
11
Nicole Albers
UVIS Team Meeting, Boulder, January 2010
B ring edge variability
Azimuthal changes:
Material at the edge forms into sub­km +/­90deg from Mimas which dissolves further downstream
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Temporal changes:
Increase optical depth
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Increase in radial amplitude
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Increase in sub­km structure
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12
Nicole Albers
UVIS Team Meeting, Boulder, January 2010
B ring edge kinematics
Mimas 2:1 ILR dominates
● m=2 pattern orientation and strength varies in time
● potential m=1 pattern (VIMS, RSS) present but few tens of km residuals ●
13
Nicole Albers
UVIS Team Meeting, Boulder, January 2010
Presence of multiple modes at the edge
free m=2
free m=1
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Nicole Albers
UVIS Team Meeting, Boulder, January 2010
B ring edge multi­mode kinematics
Streamline description:
N
r=a 1−∑i=0 ei cos[mi∗ f i ]
f i =−0 i −i∗et −et 0 
Spitale and Porco (submitted): forced m=2 + free m=1,2,3
But still unsure about the correct epoch ....
15
Nicole Albers
UVIS Team Meeting, Boulder, January 2010
B ring edge multi­mode kinematics
16
Nicole Albers
UVIS Team Meeting, Boulder, January 2010
B ring edge: Work in progress
Edge kinematics:
Further fitting requires carefully scanning the chi^2 gradients of various multiple modes
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Is the increasing optical depth directly related to the larger radial excursion of the edge? ● Is the sub­km structure related to streamline compression or is it driving the edge?
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Edge profiles:
Is there additional systematics in the edge profiles, potential time dependences?
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17
Nicole Albers
UVIS Team Meeting, Boulder, January 2010