1. Photometric observations by HDAC onboard Cassini: sensitivity and first comparison with models Yuri Skorov, Horst Uwe Keller, Ralf Reulke, Karl-Heinz Glassmeier, Vlad Izmodenov, Olga Katushkina
Lomonosov Moscow State University

2. HDAC calibration via SPICA observations
The star spectra was obtained from the INES (IUE Newly Extracted Spectra) database.
HDAC relative spectral sensitivity (UVIS Calibration Report)
HDAC off-axis response. Raster Scan 2002.

3. Pseudo normalized SPICA observations 2006-2011
Pseudo normalized SPICA observations The data from HDAC2006_037_23_32_06 was used for normalization. Observation time is s.
Scan directions of SPICA observations Angle differences between the star position and the line of sight.
Sensitivity variations across the FOV (off-axis response) are very stable.
Angular distribution of sensitivity is not axisymmetric.
Central noisy part of FOV plays only minor role for analysis of LISM hydrogen observations.

4. Sensitivity decreases very slowly. Today 11 cts/s/R.
The relative reduction in sensitivity obtained from the SPICA observations.

5. IPH observations 2011: rotational mode
Star
Fixed orientation
Hydrogen observations in Rotational mode. Integration time 4 sec.
Red curves: HDAC2011_002_00_41_24_4.0,
green curves: HDAC2011_058_21_03_20_4.0.

6. IPH observations 2008: rotational mode
Saturn position from 2001 to 2017 relative to the upwind direction of interstellar hydrogen (arrow).
For 2008 observations obtained in rotational mode give us instant scan in a plane parallel to the direction of hydrogen flow.
Hydrogen observations in Rotational mode. Integration time 4 sec. For the fixed position STD~600, MEAN~90000.

7. 3D model of the hydrogen distribution inside the heliosphere (Izmodenov&Co)
Boltzmann kinetic equation:
m=m(t,l,vr)
rE=1 AU TS
LISM
LISM
Hydrogen distribution in the heliosphere is effected by: - Local effects that are important near the Sun: (solar gravitation Fg, radiation Frad and ionization bE) - Global effects: distribution function of H atoms is distorted in the heliospheric interface due to charge-exchange => distribution function is not Maxwellian at 90 AU (Izmodenov et al., 2001) Simple self-absorption approximation for the calculation of the Lyman-alpha spectra is used (no multiple scattering)
fondue
Outer boundary is at 90 AU

8. Comparison: raw data vs. model
model data
Comparison: raw data vs. model
Time interval is only 7 days
2004/220
2004/22
2004/13
Larger amplitude
Smaller amplitude
Time
Time
Time

9. 2D stationary case for different m and b
HDAC_2011_DAY2
β - ionisation rate
HDAC observations

10. 3D and time-dependent effects
HDAC_2011_DAY2
HDAC observations

11. Variations of boundary conditions
HDAC_2011_DAY2
HDAC observations

12. CONCLUSIONS Sensitivity of HDAC is sufficient
Observations in the rotational mode allow us to obtain unique data on the 3D distribution of hydrogen
A preliminary comparison of the data with theoretical models shows that the accuracy of the observations is sufficient to verify the models
We want to perform an extensive comparison of data from HDAC and FUV to check the absolute calibration
Noise problem not solved yet, but little influence on the accuracy

13. HDAC absolute sensitivity
Comparison with absolute calibration using FUV data for 2001 and 2003 (Regehly and Reulke)