1. HDAC status and analysis: Photometric observations by HDAC onboard Cassini Yuri Skorov, Horst Uwe Keller, Ralf Reulke, Karl-Heinz Glassmeier, Vlad Izmodenov, Olga Katushkina

2. 2008
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.

3. “Catastrophic” events in 2001
Overview of HDAC photometer data for 2001 and 2002.

4. SPICA observations: Off Axis Response
HDAC off-axis response. SPICA Raster Scan 2002
The off-axis response was measured in the laboratory (red line). Blue line – fitting curve for the raster scans, green circles – one of the scans. .
How stable is this 2D map of off-axis response?
We have raster scans for 2002 and 2003 and many single-pass observations in

5. Raster Scan. Line of Sight movement
Raster Scan. Central part of off-axis response map. 2D inhomogeneities are clearly visible
Raster Scan. SPICA data set

6. 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
0.125 s.
Scan directions of SPICA observations Angle differences between the star position and the line of sight.

7. 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.

8. HDAC calibration via SPICA observations
HDAC relative spectral sensitivity (UVIS Calibration Report)
Spica spectra for ( Flux variation over one day is clearly visible: the first spectrum is obtained at 18:15:46, the last one at 23:28:10.

9. Total FUV signal with linear trend (due to sensitivity decline) divided out. Blue line is the predicted variation in flux from the model (Greg Holsclaw, team meeting presentation).
Spica spectra (black curve) and its product with the spectral sensitivity function (red curve).

10. Sensitivity decreases very slowly. Today 11 cts/s/R.
Absolute HDAC sensitivity in counts/s/R evaluated from the Spica observations (blue curve) and LISM observations (red curve).

11. 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.

12. FUV and HDAC

14. Examples of spectra and extrapolation
IPH observations 2011: rotational mode
Examples of spectra and extrapolation

15. Example of obtained preliminary results
IPH observations 2011: rotational mode
HDAC2011_058_21_03_20
Example of obtained preliminary results
HDAC2011_124_06_18_15

16. Distribution of UV objects in the sky (from ESRO TD1 catalog)

17. IPH observations 2011: rotational mode

18. IPH observations 2008: rotational mode
During NASA scientists noted that the Sun is undergoing a "deep solar minimum," stating:
"There were no sunspots observed on 266 of [2008's] 366 days (73%). Prompted by these numbers, some observers suggested that the solar cycle had hit bottom in /wikipedia.org/

19. 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 multiply scattering)
fondue
Outer boundary is at 90 AU

20. 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

21. Comparison: raw data vs. model
Observations (red curve) for DOY The abscissa is time in simulation steps. Integration time is 4 seconds. The ordinate is dimensionless intensity of Lyman alpha emission (observation and theory). Dashed red curves = observations +- 2σ. Dark blue curves correspond to different ionization rate: solid/dashed=5. Light blue curves correspond to 3D time dependent models: solid curve for self absorption model, dashed curve for optically thin model.
DOY
HDAC
Time

22. CONCLUSIONS Sensitivity of HDAC is sufficient
Observations in the rotational mode allow 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 must perform an extensive comparison of data from HDAC and FUV to improve the absolute calibration