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Spatial Distribution of Atom Velocities in the Mercury Sodium Tail - Observation at Haleakala in June 2007 -
H. Fukazawa, M. Kagitani, S. OkanoH. Fukazawa, M. Kagitani, S. Okano Planetary Plasma and Atmospheric Research CenterPlanetary Plasma and Atmospheric Research Center Tohoku UniversityTohoku University
Potter and Killen, 2008
Previous observations of Mercury’s sodium tail
Baumgardner et al. 2008
Kameda et al. 2008
Anti-sunward velocity of sodium atoms in the tail
- [Potter et al., 2002] : ~ 20RM
- [Potter et al., 2007] : ~ 20RM - [This study] : ~ 120RM => Sodium atom velocities were derived for the region not studied before.
Potter and Killen, 2008
June 6, 2007
This study
20RM
Observation- Date (UT) : June 6; 8; 10; 11, 2007 05:00 ~ 06:30LT (evening twilight)
- Site : Haleakala observatory, Maui island (20.7 ゚ N 156.3 ゚W 3040m )- Telescope : 40cm Schmidt Cassegrain ( F/10.9 )- Spectrograph : Echell High Resolution Spectrograph
- Data : 1dataset => equator = 1 frame, North-South = 3 frames
- Slit Width : 50 – 90 μm
- Plate Scale : 0.85”/pixel, 2.1 pm/pixel
- Spectral Resolution : λ/ λ⊿ ~ 70,000 @ 589nm
- Exposure time : 300 – 840 sec
Slit position on June 6.
N
S2.5Rm( 5,580km)
8Rm( 19,500km)
17Rm( 41,900km)
Spectral image with slit aligned anti-sunward direction
Terrestrial Na airglow
Na emission on Mercury
Example of spectral image (June 6, 2007)
Sun
Earth
Mercury θPA
Vt
VLOS
cVLOS
90sin PA
LOSt
VV
Geometry of the Sun, Mercury, and the Earth
Date
(UT)
TAA
(Degrees)
PA
(Degrees)
Heliocentric Distance
(AU)
Radial Velocity,
(km/sec)
Solar Radiation Acceleration,
(cm/sec2)
6/6/07 134.9 114.5 0.433649 7.05 87.5
6/8/07 141.2 119.4 0.441392 6.24 73.1
6/10/07 147.3 124.5 0.448213 5.37 55.8
6/11/07 150.3 127.0 0.451231 4.93 46.6
Planetary configuration on June 6–11, 2007
Derivation of sodium anti-sunward velocity
VLOS: LOS velocityVt : tailward velocityc : light velocity : Doppler shift : D2 line wavelengthθPA : phase angle
Anti-sunward velocities of sodium atoms on June 6, 2007Anti-sunward velocities of sodium atoms on June 8, 2007Anti-sunward velocities of sodium atoms on June 10, 2007Anti-sunward velocities of sodium atoms on June 11, 2007
Non-uniform accelerations, exceeding error bars, are seen in the data.
Sodium brightness in the tail on June 6, 2007Sodium brightness in the tail on June 8, 2007Sodium brightness in the tail on June 10, 2007Sodium brightness in the tail on June 11, 2007
Non-uniformities are also seen in sodium brightness (noticeable on June 8).
Bri
ghtn
ess
[kR
]
1
0.1
10
100
1000
Distance from Mercury center [RM]
0
40 80 120
Comparison between sodium velocity and brightness
■ At regions where velocity non-uniformity is seen, brightness is also increased.
Velocity and brightness of sodium atoms in the tail on June 8 and 10, 2007.
Velocity of sodium atoms at a distance of 20RM to 50 RM from Mercury center on June 8, 2007.
Time scale of velocity change
~ 20min~ 20min
Conclusions
- Non-uniform acceleration of sodium atoms was identified in the tail. - Time scale between successive non-uniform acceleration is about 20 minutes.
Future Strategy
- Simulation of Mercury magnetosphere
- 3-D simulation of the sodium tail
Combining above two simulations, we may reproduce what is happening on Mercury.
- Another observation
Date
(UT)
TAA
(degrees)
PA
(degrees)
Heliocentric Distance
( AU)
RadialVelocity
(km/sec)
Solar Radiation Acceleration
(cm/sec2)
06/27/08 238.3 118.5 0.415636 -8.65 115
07/03/08 260.9 101.1 0.383247 -10.3 151
07/10/08 292.9 78.4 0.343348 -9.38 180
07/14/08 314.4 63.0 0.324070 -7.30 164
Table.2. Planetary configuration in June-July, 2008
Mercury orbit.
outleg
inleg
Energy needed for escape[Potter et al, 2008]
TAA
Sun
Mercury
apherion periherion
Next Observation - Purpose : to get more positive results on the non-uniform acceleration - Necessity : sufficient S/N and spatial resolution - Time window : end of June – early July this year
Data processing and Error estimation
ガウシアンフィッティングNO
binnig
10000 times loop
wavelength error in fitting
calculate 1
Estimation of sodium velocity error.
Tail Spectroscopic Data
ガウシアンフィッティングGaussian fitting
OK
Smoothed Tail Data
Random readout noise is added
Noise added tail data
Gaussian fitting
Determine center pixel
histogram of center pixel