HDAC Data on Titan
Current Status of HDAC Analysis
Yuichi ITO1*, Horst Uwe Keller1, Axel Korth1 , Ralf Reulke2
1 : Max-Planck-Institut für Sonnensystemforschung, Katlenburg-Lindau,
37191, Germany
2 : Deutsches Zentrum für Luft- und Raumfahrt, Institut für Verkehrsforschung,
Rutherfordstraße 2, 12489 Berlin, Germany
E-mail : ito@mps.mpg.de
TEL: +49-5556-979-124, FAX: +49-5556-979-240
20060710, UVIS team meeting in Boulder
Outline
1. Review T9 data
2. Current status (software, status)
3. Summary & future plan
Dark: H=0 & D=0 (Background)
Blue: H=7 & D=0
Green: H=7 & D=7
(1)Signal from 13-19 kct/s ~ 460-680 [R] (raw data)
(2)Max modulation
~ 0.92 (raw data)
1. Review T9/PHASE2 data
Titan 9th encounter on Dec26, 2005
F10.7 = 89.5
Raw data
HDAC viewed Titan disk
HDAC viewed limb of Titan
680[R]
Measured ct/s
2.0*10^4
downtrend
uptr
end
1.6*10^4
460[R]
1.2*10^4
UTC
20:03
T9/PHASE2 end
12
Distance to
Target
[1000km]
FOV orientation changed
at this moment
18:59
Closest approach
17:53
T9/PHASE2
start
26
0
6 -15
Absolute
deviation
from Target
[deg]
-6
Doppler
speed
[km/s]
Distance of
Titan(black)
and FOV
15
0.5
1.0
1.5
2.0
Time [hr]
Intensity [arbitrary]
(1)Determination of Non-LyA component
FUV spectrum
Spectrum convoluted by
HDAC sensitivity
100
120
140
160
180
200
Wavelength [nm]
Convolute HDAC sensitivity & FUV spectrum
(1)100-121.45nm,(2)121.45nm-121.65nm,(3)121.65nm-200nm.
Non-LyA = ( (1)+(3) )/( (1)+(2)+(3) )
Non-LyA : 0.598
(2)Consideration of outflow effect
s/c Dopplershift + outflow
H-LyA
s/ c
Dop
p
lers
hift
H-LyA
H-LyA
A velocity of ~2km
outflow is expected
Collisiondominated
Collision-less
Free-particle
Exobase
trajectory
(1500km)
Visible region
Invisible region
A schematic diagram to show the
concept of outflow
Exospheric
Line profile
Wavelength direction
HDAC profile
Titan
Only s/c Dopplershift
In our case, we assume that the
outflow speed is equal to the thermal
velocity
2. A comprehensive analysis program for T9 observations
T9 obs data
Analysis model
(1)Ly-A radiative transfer model
(2)Line profile simulation
(3)Orbit simulater (SPICE-Kernel )
(4)Dopplershift correction by outflow effect in
exosphere (* See data interpretation)
Transmission of
Hydrogen cell
Transmission of
Deuterium cell
BG information
Measured signal
Comparison module
( Chi-squares fitting )
And
Inversion module
Hydrogen density
(by inversion algorithm)
Exospheric
temperature
Doppler shift
Lyman alpha
flux
Our goal
Scheme of HDAC analysis
3. Application of the Model
Conditions
•
•
•
BG-level
: 60% of measured signal(fix)
Used DATA : 17:53-18:53 (Nadir observation)
H-LyA model : Single scattering
HDAC conditions
•
•
•
H-cell cycle : 0777777777777777
HDAC cell : 300K,
optical depth 0.86
Îsearch for exospheric temperature & exospheric density
BG_percentage: 60%
CELL
: 300K, tau = 0.86
Exospheric temperature is ~550K
Comparison (Obs & Cal)
Exospheric temperature
Obs (H OFF)
250
600
Cal (H off)
Cal (H on)
150
50
FOV FLAG
( inside disk 1 )
0
0
20
40
60
Exospheric temperature[K]
Intensity [Rayleigh]
Obs (H ON)
400
200
0
0
80
Elapsed time after P2/start
10
15
Iterations
20
Best fit hydrogen density profile
Intensity ratio v.s. altitude
30000
30000
Nadir obs(17:53-18:53)
Radiative transfer analysis
20000
max.3000-4000km
10000
Red line: exobase (1500 km)
Altitude [km]
Altitude [km]
5
Black: Espositio‘s model
(Initial hydrogen distribution)
20000
10000
Red: retrieved hydrogen
distribution
0
0
0.0
0.1
0.2
0.3
Ratio
0.4
0.5
0.6
10-5
100
105
Number Density[1/cm3]
1010
Expected exospheric temperature
Past measurements:
•
•
Voyager UVS measurement :186+-20 K at 3840 km (Smith et al)
Cassini INMS : 149K+-3K at exobase (1150km-1550km) : (By
the upward flux estimated from CH4 distribution, J.Waite)
Theoretical description:
•
Lellouch: exospheric temperature at solar minimum could be as
low as 130 K and could exceed 300 K during solar maximum (Ip,
1996, Astrophysical Journal v.457, p.922 )
T9: F10.7 = 89.5
(near solar minimum)
Interpretation of Retrieved Temperature
Exospheric temperature is too high (550K) for a cell temperature of 300K.
Why?
ÎThe value of the R.R (modulation) deviates from the actual observations.
Î The R.R is dependent on the following 3 parameters:
Hcell ON
R.R =
Hcell OFF
(1)Subtraction of BG-level
We assumed 60% of signal is BG-level. We need FUV albedo
information!
(2) HDAC parameters
300K is assumed for HDAC cell. Uncertainty is 270K to 330K in the
calibration report.
(3) Outflow effect
(1)No detailed consideration of FOV and its direction.
(2)No consideration of phase angle(30-90deg )
(3)Assume outflow velocity equals to thermal velocity
Summary
We have been developing a comprehensive HDAC analysis program for
retrieval of hydrogen distribution and exospheric temperature. However, there
are no real conclusions yet.
Retrieved quantity
(1) Retrieved temperature is 550K.
(2) Retrieved density profile is smaller than Esposito’s model.
Future plan
(1) HDAC temperature width
(2) Determination of BG-level (FUV albedo)
(3) More detailed analysis of outflow effect
(3-1) in relation with FOV & its orientation,
(3-2) Doppler shift correction by partition function