Title: Magnetometry of the Solar Corona through UV Spectropolarimetry
1Magnetometry of the Solar Corona through UV
Spectropolarimetry
- Achim Gandorfer, Udo Schühle, Sami Solanki
- Max Planck Institute for Solar System Research
2Magnetic 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
3Solar magnetometric techniques
4Zeeman effect
5Hanle diagnostics
- Hanle effect Modification of scattering
polarisation in the presence of a magnetic field
6Hanle 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!
7Zeeman 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
8When 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
9Magnetic 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)
10Magnetic 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
11Magnetic 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
12What 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
13How can this be done?
- UV polarimetric mission in space
- large telescope
- high data rate
- VUV spectroscopy
- polarimetry
14What 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
15Who is COMPASS?
mission proposed to ESA in response of the call
for ideas for the Cosmic vision program 2015-2025
16COMPASS 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
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19COMPASS mission scenario
20COMPASS Formation Flying Spacecrafts
Sunward Spacecraft (SW-S/C)
Sunshaded Spacecraft (SS-S/C)
Occulter/ Solar Panels
Solar Panels
21COMPASS Off-Disk Payload
Coronagraphic UV Spectro-Polarimeter
Coronagraphic VIR Spectro-Polarimeter
S/C Service Module
Solar Panels
22COMPASS On-Disk Payload
EUV Imager-Polarimeter
Occulter/ Solar Panel
Dopplergraph- Magnetograph
Disk UV Spectro-Polarimeter
S/C Service Module
23P/L Dimensional Envelopes (TBC)
1.5 m
30 cm
60 cm
24Sunward 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
25Shadow 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
26Coronagraphs 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
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32Telescope
scanning single mirror telescope similar to
SUMER 1 resolution 6 field (slit length)
instant. 1 squared FOV (scan range)
33Polarimetric analysis
MgF2 rotating retarder Brewster plate stack as
analyser can be moved out of beam
34Spectrograph
dispersion magnification single element design
(TVLS) spectral band 115nm-155nm
35detector / focal plane assembly
1 large microchannel plate 1 fiberoptic coupler
3 2kx2k APS
36next 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