Rev 51 Enceladus
Zeta Orionis Occultation
Analysis Status
9 January 2008
Enceladus Plume Occultation
In Rev 51 zeta Orionis was occulted by Enceladus’ plume
This is the perfect geometry to get a horizontal cut through the plume and
detect density variations in the gas jets
Enigmatic Enceladus
High density dust jets
Are there corresponding high density gas
streams?
Outline
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•
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FUV analysis
HSP data
Jets / probability
Location of jets
Comparison to models
FUV analysis
Occ is easy to detect
Star drifted from pixel 13 to pixel
12 over the course of the
observation
FUV analysis
Plume occults zeta Orionis in time records 89 and 90
Signal falls into spatial rows 11 to 15, summed for these spectra
Integration time = 5 sec
Water column density: FUV, Ian’s analysis
Two occulted time records combined
Column density derived from short wavelength region of spectrum
and from long wavelength region gives different but similar values
Water column density: FUV, Candy’s analysis
Time record 89
Mota 2005 cross-sections
Best fit column density = 1.5 x 1016 cm-2
Column density almost
identical to 2005
Time record 90
Mota 2005 cross-sections
Best fit column density = 1.65 x 1016 cm-2
HSP Data: Bonnie’s analysis
•
Statistical analysis applied
to find features that are
probably real
•
Assumes signal is Poisson
distribution
•
Six different bin sizes
employed
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Possible real features:
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•
•
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1 (b) m = 0.032
2 (c) m = 0.000008
3 (d) m = 0.00056
6 (e) m = 0.026
HSP Data, summed to 200 msec
a. Ingress
f. Egress
e. Damascus III
b. Cairo (V)
c. Cairo (VIII)
or Baghdad (I)
d. Baghdad (VI)
Closest point
Start time: 2007-297T16:59:49.735
Closest point to limb: 17:07:20.8
Deepest absorption: 17:07:21.0
Hot Spot Locations (Spitale & Porco, 2007)
Start to end
a) Ingress
b) Cairo V
c) Cairo VIII or
Baghdad I
Closest to limb
End
f
e
d
b
c
d) Baghdad VI
e) Damascus III
a
f) Egress
S/c viewed
from this side
Start
Hot Spot Locations (Spitale & Porco, 2007)
End
Start to end
Cairo V
Cairo VIII or Baghdad I
Baghdad VI extension?
Closest to limb
Baghdad VI no absorption
Damascus III
Start
Precise geometry polar plot
• Asterisks show possible absorptions in UVIS data
• Circles show clusters of dust jets visible in images
FUV - HSP Comparison Work in Progress
Times of two FUV integrations
Since these are averages over 5 sec the peak density at plume
center could be 2 - 2.5 x higher
Ray height from ingress to egress
Ray height from ingress to egress
50
45
40
km altitude of star
35
30
25
20
15
10
5
0
1
3
5
7
9
11
13
15
17
19
21
23
25
Trajectory kernels from 071114_052T37_alleph.bsp
Reconstruction, not quite final
27
29
31
33
35
37
39
41
43
Optical Depth vs. Rayheight
Best fit: z-2.3
Optical Depth vs. Time
Monte Carlo model results - Predicted Plume Shape
Work in Progress
Occultation Track across plume model
Summary of Results
• Column density in 2005 ~ = 2007 ~ = 1.6 x 1016 cm-2
• Peak density may be 2 - 2.5 higher
• HSP data shows 2 - 4 features which may be real
• Possible to correlate to dust jets mapped in images
• Change in opacity is minimal however - gas streams do not
appear to be as collimated as dust jets
• Plume density structure still best characterized as ~z-2.3 where z
is rayheight
• Consistent with simple Tian et al model
Future Plans
• LPSC
• EGU
• GRL Paper