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SHINE 2008

Vector Magnetic Fields from the Helioseismic and Magnetic Imager. Steven Tomczyk (HAO/NCAR) Juan Borrero (HAO/NCAR and MPS). SHINE 2008. From Juan Borrero. SHINE 2008. Basic problem is to infer properties of magnetic field from observations of the Stokes profiles.

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SHINE 2008

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  1. Vector Magnetic Fields from the Helioseismic and Magnetic Imager Steven Tomczyk (HAO/NCAR) Juan Borrero (HAO/NCAR and MPS) SHINE 2008

  2. From Juan Borrero SHINE 2008

  3. Basic problem is to infer properties of magnetic field from observations of the Stokes profiles. Historically there have been two classes of instruments. Magnetographs and Spectropolarimeters… SHINE 2008

  4. Magnetograph Instrument with typically poor spectral resolution and good spatial resolution. Few samples across line profile. Usually only Stokes V - LOS Flux Density Examples: BBSO, GONG, KPNO, MDI Pro: Fast Temporal cadence Con: LOS Flux density, saturation (systematic errors) SHINE 2008

  5. Spectropolarimeter Instrument with typically good spectral resolution and moderate spatial resolution. Many samples across line profile. Usually spectrograph, I, Q, U, V Allow inference of vector field (B and geometry) Examples: ASP, Hinode SP, IVM, SOLIS Pro: Very precise Con: Slow to acquire map (Hinode SP - 15 minutes, partial Sun), complicated and slow data inversion SHINE 2008

  6. HMI - Imaging Spectropolarimeter Full Sun image - 1 arcsecond resolution (4096x4096) Full Stokes I, Q, U, V with 6 samples across FeI 617.3 nm line Allows inference of vector magnetic field Full magnetic information every 90 seconds - 10 minute cadence for standard data product Precision is not as good as Hinode SP but very fast SHINE 2008

  7. SHINE 2008

  8. HMI will have: • Full Disk Coverage • High Temporal Cadence • Continuous Observations • Evolution of magnetic structure of sunspots and active regions • Magnetic shear accumulations and impulsive release • Evolution of helicity in active regions SHINE 2008

  9. Vector polarimetry with HMI • Full Stokes I,Q,U,V allows inference of Vector Magnetic Fields • More accurate velocities in the presence of magnetic fields through removal of Q, U & V to I crosstalk • Flows around sunspots, Sunspot seismology • More accurate flux determinations • Total flux, as opposed to longitudinal • True full disk magnetometry • Limb fields, polar fields SHINE 2008

  10. Stokes Inversion SHINE 2008

  11. HMI inversion code Very Fast Inversion of the Stokes Vector (VFISV) by Juan Borrero • Provides inference of: • Magnetic Field Strength • Total Magnetic Flux • Inclination • Azimuth and Errors • Filling Factor • Line-Of-Sight Velocity • Thermodynamic Properties Milne-Eddington radiative transfer Initial guess with Neural Network and Weak Field Approximation Quick look and full inverted data product Macroturbulence and damping not fit Look up table for Voigt/Faraday functions Works with high or low spectral sampling data Very fast SHINE 2008

  12. How precisely will HMI and VFISV infer the properties of the vector magnetic field? Simulations by Juan Borrero SHINE 2008

  13. HMI Expected Errors We expect to see saturation starting at about 4000 Gauss SHINE 2008

  14. SHINE 2008

  15. 180º Ambiguity Resolution Is a fundamental problem Growing confidence in our ability to resolve it HMI will provide resolved vector field SHINE 2008

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