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Magnetometry of the Solar Corona through UV Spectropolarimetry

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FOVs of VIR Coronagraph. at differnt S/Cs roll angles. Slit's FOV of the. UV Coronagraph (the telescope points at different heights by tilting the mirror) ... – PowerPoint PPT presentation

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Title: Magnetometry of the Solar Corona through UV Spectropolarimetry


1
Magnetometry of the Solar Corona through UV
Spectropolarimetry
  • Achim Gandorfer, Udo Schühle, Sami Solanki
  • Max Planck Institute for Solar System Research

2
Magnetic Coupling in solar atmosphere
  • Coronal heating and
  • eruptions
  • ?
  • Complex coronal
  • magnetic structure
  • ?
  • Distribution and
  • evolution of
  • photospheric
  • magnetic flux
  • ?
  • Emergence of new
  • flux and interaction
  • with convection

The layers of solar atmosphere are coupled by
Magnetic field
3
Solar magnetometric techniques
4
Zeeman effect
5
Hanle diagnostics
  • Hanle effect Modification of scattering
    polarisation in the presence of a magnetic field

6
Hanle effect
  • depolarisation
  • independent on field orientation
  • rotation of the polarisation plane
  • depends on field orientation
  • N.B. For unresolved mixed polarity fields there
    will always be a depolarisation effect!

7
Zeeman polarimetry
  • Ideal remote sensing of strong isolated field
    components
  • Works if Zeeman splitting is comparable to
    Doppler width order of 1 kG
  • Works best in photosphere
  • splitting scales with ? works best in near IR
  • Sensitive to cancellation effects needs high
    spatial resolution

8
When does the Hanle effect work?
  • Needs scattering polarisation (second solar
    spectrum)
  • works from upper photosphere through chromosphere
    to corona
  • works best in UV
  • Works if Zeeman splitting is comparable to
    natural line width 0.1 ... 100 G
  • needs very high polarimetric sensitivity

9
Magnetic coupling science
  • Study the processes that produce and shape the
    magnetic field in the solar interior (dynamo
    theory MHD of magnetic fields in convection
    zone)
  • Study the photospheric drivers of the dynamics in
    the upper solar atmosphere (high resolution
    spectro-polarimetry, 3D MHD simulations)
  • Measure and compute the magnetic field above the
    solar surface (novel spectro-polarimetry,
    magnetic field extrapolations and stereoscopy)
  • Study the influence of the field on the upper
    atmosphere (EUV imaging and spectroscopy, plasma
    theory)

10
Magnetic coupling science
  • Study the processes that produce and shape the
    magnetic field in the solar interior (dynamo
    theory MHD of magnetic fields in convection
    zone)
  • Study the photospheric drivers of the dynamics in
    the upper solar atmosphere (high resolution
    spectro-polarimetry, 3D MHD simulations)
  • Measure and compute the magnetic field above the
    solar surface (novel spectro-polarimetry,
    magnetic field extrapolations and stereoscopy)
  • Study the influence of the field on the upper
    atmosphere (EUV imaging and spectroscopy, plasma
    theory)

Solar Orbiter science
11
Magnetic coupling science
  • Study the processes that produce and shape the
    magnetic field in the solar interior (dynamo
    theory MHD of magnetic fields in convection
    zone)
  • Study the photospheric drivers of the dynamics in
    the upper solar atmosphere (high resolution
    spectro-polarimetry, 3D MHD simulations)
  • Measure and compute the magnetic field above the
    solar surface (novel spectro-polarimetry,
    magnetic field extrapolations and stereoscopy)
  • Study the influence of the field on the upper
    atmosphere (EUV imaging and spectroscopy, plasma
    theory)

COMPASS science
12
What needs to be done?
  • explorative phase
  • uncharted second solar spectrum from 100-300nm
  • diagnostic phase
  • use Hanle effect in selected UV spectral lines
    for direct magnetometry of the solar corona

13
How can this be done?
  • UV polarimetric mission in space
  • large telescope
  • high data rate
  • VUV spectroscopy
  • polarimetry

14
What is COMPASS?
  • Coronal Magnetism, Plasma and Activity Studies
    from Space (COMPASS)
  • understanding the origin and evolution of the
    Suns magnetic field and its interaction with the
    heliospheric plasma

15
Who is COMPASS?
mission proposed to ESA in response of the call
for ideas for the Cosmic vision program 2015-2025
16
COMPASS observables
  • polarization in spectral lines in EUV wavalengths
    (IR vis.)
  • no theoretical aspects here
  • see talks by
  • Manso Sainz et al. tomorrow
  • Raouafi et al. tomorrow
  • here only conceptual/technical aspects

17
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19
COMPASS mission scenario
20
COMPASS Formation Flying Spacecrafts
Sunward Spacecraft (SW-S/C)
Sunshaded Spacecraft (SS-S/C)
Occulter/ Solar Panels
Solar Panels
21
COMPASS Off-Disk Payload
Coronagraphic UV Spectro-Polarimeter
Coronagraphic VIR Spectro-Polarimeter
S/C Service Module
Solar Panels
22
COMPASS On-Disk Payload
EUV Imager-Polarimeter
Occulter/ Solar Panel
Dopplergraph- Magnetograph
Disk UV Spectro-Polarimeter
S/C Service Module
23
P/L Dimensional Envelopes (TBC)
1.5 m
30 cm
60 cm
24
Sunward S/C Dimensional Envelopes (TBC)
1.3 m
EUV Imager-Polarimeter
1 m
1.6 m
Dopplergraph- Magnetograph
1 m
1.5 m
Disk UV Spectro-Polarimeter
25
Shadow of the Sunward S/Cs Occulter on the
Coronagraphs
1.3 m
30 cm
1.6 m
60 cm
Sunward occulter umbra
Sunward occulter penumbra
26
Coronagraphs Fields-of-View
Slits FOV of the UV Coronagraph (the telescope
points at different heights by tilting the mirror)
FOVs of VIR Coronagraph at differnt S/Cs roll
angles
27
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32
Telescope
scanning single mirror telescope similar to
SUMER 1 resolution 6 field (slit length)
instant. 1 squared FOV (scan range)
33
Polarimetric analysis
MgF2 rotating retarder Brewster plate stack as
analyser can be moved out of beam
34
Spectrograph
dispersion magnification single element design
(TVLS) spectral band 115nm-155nm
35
detector / focal plane assembly
1 large microchannel plate 1 fiberoptic coupler
3 2kx2k APS
36
next steps
  • chances for COMPASS extremely low
  • good for SolarOrbiter !
  • COMPASS should be seen as a model mission
  • also smaller, bilateral missions or even a
    national initiative for a pure spectropolarimeter
    are an option
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