UVIS HSP occultations
and ring structure
UVIS team meeting,
Goslar, June 12, 2007
Goslar,
Miodrag Sremčević
LASP, CU Boulder
M. Sremčević: Rings microstructure
2
Excess light in UVIS HSP
At the ring edges there is more coming light into
HSP detector compared to empty space!
Gam Peg Rev 36
(HSP counts)
Encke gap
UVIS team meeting
Outer A ring
Goslar, June 12, 2007
M. Sremčević: Rings microstructure
3
Zet Per Rev 42 (ingress)
(HSP counts)
Zet Per Rev 42 (egress)
(HSP counts)
UVIS team meeting
Goslar, June 12, 2007
M. Sremčević: Rings microstructure
4
Zet Oph Rev 26
(HSP counts)
Lam Sco Rev 29
(HSP counts)
UVIS team meeting
Goslar, June 12, 2007
M. Sremčević: Rings microstructure
5
More light at the ring edges than counts from the star?
The only explanation: some sort of diffraction or light
scattering effect.
Difraction on the ring edge does not match predictions!
Diffraction onto the edge: Voyager RSS example
UVIS team meeting
Goslar, June 12, 2007
M. Sremčević: Rings microstructure
6
Plausible explanation: diffraction onto the ring particles!
Ring
Gap
directly
transmitted
light (solid)
+”half” of
diffracted
component
Cassini RSS
I 1=I 0∗exp−2 /
+diffracted
light (dashed)
Cassini HSP
I 2=I 0∗exp−/
Cassini HSP
I 3=I 0 I I 0
 I ≤I 2−I 1 /2
UVIS team meeting
Goslar, June 12, 2007
M. Sremčević: Rings microstructure
7
Excess light is well above the noise level!
Appears at all ring and gap edges (A, B rings & Cassini
division).
Consistent with scattering onto ring particles
(spatial dimensions indicate few cm – 10cm sized
particles)
Excess light  I is 2-3 times smaller than simple
prediction: only particles of favorable size do contribute.
Probing the rings for particle size!
Work in progess...
UVIS team meeting
Goslar, June 12, 2007