Transcript Diapositive 1

New results in polarimetry of
planetary thermospheric
emissions: Earth and Jovian cases.
M. Barthelemy (1), J. Lilensten (1), C. Simon (2), H. Lamy(2), G Gronoff (3),
H. Menager (1), S. Miller (4), M. Lystrup (5), H. Rothkael (6), J. Moen (7).
(1)IPAG, France
(2)BIRA-IASB, Belgium
(3)NASA, Langley,VA, USA
(4)UCL, UK
(5)University of Colorado, USA
(6)Polish Space Research Center, Poland
(7)University in Oslo, Norway
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Polarization processes
• Impact polarization
Polarization rate
depends of:
– Pitch angle
distribution
– Kind of particles
– Energy
– Depolarization
processes as
collisions.
• Emission in an
anisotropic region:
for ex Electric field.
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Ex. Lyman alpha polarization rate by
electron impact. Laboratory measurement
(from James et al 1998).
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Earth case: POLARLIS,
or the measurement of the POLarization of the Oxygen
thermospheric Red Line In Svalbard.
Photo-polarimeter: SPP at KHO in Longyearbyen
(Svalbard) and at Hornsund .
Channel 1: Photomultiplier.
Red filter centered on 6300 A with a
FHWM of 1 nm.
Linear polarization analyser. One
rotation of the analyser every 4.02 s.
Channel 2: Same, without the
polarization filter.
Steerable Polarization Photometer (SPP)
built at the Oslo University (UiO). It includes
2 channels and a pan-tilt unit. Aperture is
2°.
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17 jan 2007 late afternoon. From Lilensten et al. 2008. GRL
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Reassessment
-Error in calibration angles. Correction around 45°
-New measurements at Hornsund (no light
pollution)
-Confirmation of the detection
-But rates around 1% after data processing
-Direction close to the vertical (difference was
due to the pollution)
-Compatible with Bommier et al. 2011
-Raw polarisation before depolarizing
collisions: ~18%
-Vertical ie //B
- Barthelemy et al. submitted 2010.
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Jovian case
• H3+ emissions in the IR.
• The emission process is different: No emission
due to electronic impact because of the chemical
process of formation, but…
• Possibility to get alignment due the electric fields
in the auroral region.
2 half nights observation for August 2008 at the
UKIRT with the instrument UIST-IRPOL in the Long L
band (3.6-4.2 µm). Barthelemy et al. 2010, submitted
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Seventh data set:
I at 3.95µm
q (Normalized Stokes parameter)
u (Normalized Stokes parameter)
p (%) (Debiaised)
Θ (°) (ref is the slit direction)
v (Normalized Stokes parameter)
The polarization direction are
difficult to interpret…
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Interpretation:
Conclusion and Perspectives
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Jovian case.
•Auroral UV emissions.
•Lyman  , the most promising:
•Very intense (100 kR)
•Emission due to electrons and/or protons. Various
polarization rate and direction with the energy.
•Radiative transfer in a presence of magnetic field for
an allowed transition.
•Due to this, possible variation of the polarization rate
along the line profile. Need for very high resolution.
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Needed in a dream world
• Spatial resolution around 100km2
• Width of the oval ~200km.
• Spectral resolution
• Lyman alpha width is 0.02 nm and it exists H2 lines in
coincidence with H-Lyman alpha.
• Typical lyman alpha filter width (~5nm) Some lines of
H2 but faint compared to H-Lyman alpha
• Polarimetric accuracy under 1%
• Only in the night side (dayside emission can
reach 10% of the auroral emission!)
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Feasability
• Flux (at Ly alpha)
• Expected spatial resolution:100 km2
• 100 kR in the oval (i.e. 1e11 ph.cm-2.s-1 averaged in all directions).
• Orbit : for example EJSM in resonance 2:1 with Europa i.e. around
106km for the centre of the planet
i.e. 7.9 10-1 ph.cm-2.s-1
Need an effective area of the instrument of 12.5 cm2 on a basis of
10ph.s-1. pix-1 (with an efficiency of the optics of 0.05, this
correspond to an aperture of 250cm2)
Pb moving pieces!!!
• With a “better” orbit (more flux) : example of JUNO.
Polar orbit.
Closest point 4000km
~12000km above the oval.
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Spectra/Lyman alpha filter
• Interest of spectra:
• H2 lines
• No mixing between H2 and Lyman alpha lines if
sufficient resolution.
– But not enough flux considering EJSM orbits
to get H2 lines.
– And possible problem with the grating.
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Optical solution?
• Exemple: SMESE-Lyot like design
(mirrors)
From Auchere et al. 1st SMESE workshop.
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Conclusions
• Difficult design due to the short wavelength
– But
• Strong interest
• Best solution?
• Mission to the planet (EJSM; too late for Juno)
VS
• Space telescope
• Rq: Saturn has Ly alpha aurora 10 times
fainter.
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Perspectives and needs.
• Diversity of processes,diversity of emissions
→Specific information for each line and planet.
• Others examples :
– O 8446 Å, O 1304 Å* (Earth, Venus, Mars)
– Na I 5890 Å (Mercury)….in progress
– Needs for the jovian case
– Ab initio calculation of the link between H3+ lines
polarization and the fields (E and/or B).
– Lab experiment.
– In EJSM frame: Difficult to have a Ly alpha polarimeter. H3+
measurement as combined measurements
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Polarisation as a tool to study
the Solar System and beyond
COST proposal reference: oc-2010-2-8667
Hervé Lamy1 & Mathieu Barthélemy2
1 Belgian Institute for Space Aeronomy (BISA)
2 Institut de Planétologie et d’Astrophysique de
Grenoble (IPAG)
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