1. Update on Lyman-alpha from Cassini, and Voyager
Wayne Pryor
Central Arizona College

2. IPH surveys- where we are now-
Data processed up to June 2005
Modeled every 1 minute with optically thin model using C-kernels and geometer up to Dec. 2004
To fit the rotating data from 2004, need asymmetric solar wind H lifetime (A=0.8): reflects enhanced equatorial solar wind at solar minimum
Subtracting model from near-Saturn data leaves H cloud (extended in equatorial plane)
Comparisons with Voyager data from ongoing

3. Calibration change: 139 (new data) vs. 29 (old data)
Normalized in wings
Ratio of peaks is 0.71
At start of mission,
IPH data=0.8*model
Now
IPH data=0.55* model
Note 0.8*0.7=0.56

4. 2004 IPH Data and Model

5. A=0 Model: symmetric solar wind (not too good…)

6. A=0.8 case: asymmetric solar wind (better)

7. H cloud result: 2004

8. New effort- Voyager 1/ Cassini Lyman-alpha comparison (2003.5-2004.5)
Voyager 1 at A.U. from Sun
Looking upwind
Voyager 1 at 34 N ecliptic latitude
Cassini is downwind, in ecliptic plane
Solar rotational modulation is seen in both
Goal is to constrain the density from the degree of damping.

9. UVIS “upwind” Modulation 2003-2004

10. Voyager 1 modulations

11. Voyager 1 and thin model (model bump can be missing if active region source is S. V1 is N)

12. Voyager sees waves damped by about a factor of 6

13. H density Published results for the H density vary widely
This reflects inconsistent UV calibrations (scaled Galileo derived model by 0.8 to fit Cassini)
Galileo model had n~0.17 cm-3, Cassini had n~0.14 cm-3
To examine the H density nH, we will assess modulation damping with distance:
Near the Sun, at low H optical depth, amplitude modulation of interplanetary Lyman-a should be close to modulations of solar Lyman-a
At large distances & large H optical depths, amplitude modulation of sky H should be greatly reduced by multiple scattering
Shemansky et al. (1984) found Lyman-alpha was optically thick in Voyager data, nH at large distances (but inside the termination shock) to be ~ cm-3.
Quemerais et al. (1996) found nH=0.15 +/ cm-3

15. What H data sets are we using?
Spacecraft Lyman-a Lyman-b Start End
Ulysses x ?
Galileo x x
Cassini x x ?
Voyager

18. Cassini Data and Geometry

19. 2002 period with good modulation

21. Cassini Results
Solar rotation modulation of Lyman-a occurs past Jupiter.
Our models (e.g. Pryor et al., JGR, 2003), single scattering models with fixed multiple scattering correction, describe the modulations seen.
The absence of strong modulation damping suggests Cassini is in the single scattering region for solar photons.
Hall 1992 find Lyman-a line-center optical depth 1 occurs over a path length of ~10 AU for nH=0.1 cm-3
When Saturn (semi-major axis 9.54 AU, period 29.4 years) is upwind, this applies,
Cassini is now downwind, so the optical depth is lower because the heliospheric cavity is elongated downwind.

22. Galileo EUV data show similar modulations

23. Cassini UVIS and Galileo EUV

24. Voyager 1 and Sun

25. Quemerais et al., 1996 figure for nH=0.15

26. Quemerais et al., 1996 figure for nH=0.15

27. Damping with density

28. To do…
Get SWAN and Ulysses GAS upwind data to test solar model and compare line-center to line-integrated modulation
Complete Cassini and Galileo modeling for 1-10 A.U. cases
Run Quemerais-type model for the Voyager modulation damping
Constrain hydrogen density.

29. Voyager / Cassini anticorrelated