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. Historically there have been two classes of instruments. Magnetographs and Spectropolarimeters…

SHINE 2008 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 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 HMI - Imaging Spectropolarimeter Full Sun image - 1 arcsecond resolution (4096x4096) Full Stokes I, Q, U, V with 6 samples across FeI 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

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 ● 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 Vector polarimetry with HMI

SHINE 2008 Stokes Inversion

SHINE 2008 HMI inversion code Very Fast Inversion of the Stokes Vector (VFISV) by Juan Borrero Provides inference of: Magnetic Field Strength Total Magnetic Flux Inclination Azimuthand 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 How precisely will HMI and VFISV infer the properties of the vector magnetic field? Simulations by Juan Borrero

SHINE 2008 σ B (Gauss) σ Inclination (deg) σ Azimuth (deg) σ Vlos (m/s) Sunspot Plage Network HMI Expected Errors We expect to see saturation starting at about 4000 Gauss

SHINE 2008

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