Spectral Line Performance Using Inversion Codes J. Graham, A. Norton, S. Tomczyk, A. Lopez Ariste, H. Socas-Navarro, B. Lites NCAR/HAO Goal: Characterize performance of FeI 6173 and NiI 6768 over anticipated range of velocities and magnetic field parameters.

Simulations - Artificial Profiles Profiles are generated using ME parameters based on ASP Obs & Inversions - Mar 9 ‘02 FeI 6173/FeI 6302  = 1.0 ~22,000 profiles - Mar 10 ‘02 NiI 6768/FeI 6302  = 0.6 ~34,000 profiles Pixels treated identically - Random velocity (+/- 6 km/s) & random field orientation assigned - Field strength and filling factor of FeI 6302 given to both lines Apply filters, apply detector noise Use Levenberg-Marquardt least squares minimization to fit ME filtered profiles Errors between fit and true parameters provide a measure of line performance Simulations – Observed Profiles Same as above except no randomization of parameters and no ‘true’ values

 6173  x 6768 Line Performance: Velocity 6173/6768 perform similarly for low field strength and low velocities 6173 performs poorly at high B (>1700 G) and high velocities (> 3 km/s) using current filter configuration. Field Strength – 6173 performs much better  – 6173 performs much better at low flux densities

 6173  x 6768 Longitudinal Flux Density – 6173 performs better except at weak-strong field transition Transverse Flux Density – 6173 performs better except tranverse fields in weak-strong field transition Method of coarse sampling may cause hiccup in B determination in the weak-strong field transition where Zeeman splitting  Doppler width.

 6173  x 6768 Stokes I/V Only : Velocity 6173/6768 perform similarly for low field strength or low velocities In umbra, velocity errors worsen without Stokes Q & U profiles I/V Only: Longitudinal Flux Density On average, 6173 performs slightly better until high B where it moves into strong field regime. Stokes I/V Only

+ HMI x Sim * ASP 6173 B accuracy of 100 G in penumbra and umbra  and  accuracy to ~2  above 600 Mx/cm B accuracy of 400 G in penumbra and umbra  and  accuracy to ~2  above 1000 Mx/cm 2 Blends & Asymmetries in Ni worsen its performance at high flux. Observed Profiles

+ HMI x Sim * ASP Flux: 6173 does 4x better for both transverse and longitudinal components. Observed Profiles

Conclusions Using 6173: We gain up to 4x accuracy of field strength in sunspots.(100 vs 400 G) We gain up to 4x accuracy of flux, both longitudinal and transverse. We better determine orientation for Mx/cm 2 range. Velocity is not compromised unless high B and high velocity. * Velocity errors will decrease in umbra with full Stokes vector  Good news for Active region helioseismology. Challenges * Increasing the dynamic range in order to take advantage of We also need to develop an inversion technique that can handle near real time data since the current inversion techniques are time consuming.

HMI Best-Case Error Values 6173 UmbraPenumbraPlageQuiet B ( Gauss) Velocity (m/s) 50* (30)30* (20) UmbraPenumbraPlageQuiet B ( Gauss) Velocity ( m/s) *This value is high due to strong B fields causing line to move outside of filter sampling range. If we ‘chase the line’ or add more filter sampling positions then the error will be the value in parenthesis.