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Hacking Zeeman

Hacking Zeeman. Colin Folsom (Armagh Observatory). Zeeman Overview. Read input Calculate line components (Zeeman splitting) Calculate continuum opacity (per window, per atmospheric layer) Calculate line to continuum ratio (window, layer, line)

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Hacking Zeeman

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  1. Hacking Zeeman Colin Folsom (Armagh Observatory)

  2. Zeeman Overview • Read input • Calculate line components (Zeeman splitting) • Calculate continuum opacity (per window, per atmospheric layer) • Calculate line to continuum ratio (window, layer, line) • Calculate spectrum from each stellar surface element...

  3. Disk Integration • For each: rotation phase, window, surface element • Determine local field • Determine strengths of components for each line • Calculate spectrum ...

  4. LinPro • For each: phase, window, surface element, layer • For each component of each line: • Calculate Voight profile, at each point in wavelength, with polarization information(Humlicek, 1982 algorithm) • For each point in wavelength, perform radiative transfer, for 4 Stokes parameters(Martin & Wickramasinghe, 1979; Landstreet ,1988; Wade et al., 2001)

  5. Putting it together • Integration propagates through atmospheric layers • Surface elements are Doppler shifted and added • Gaussian instrumental profile applied • Windows and phases output separately

  6. Non-Magnetic Zeeman • Major time saving • Input and output compatible with magnetic • As similar routines as possible

  7. Non-Magnetic Case • Assume horizontal homogeneity • Only need a line of surface elements rather then a disk (allows for correct vsini and limb darkening) • Computation goes as vsinirather then vsini2

  8. Non-Magnetic Case • Skip separate Voight profiles for different components (save a factor of a few) • Voight profiles of one line at one layer are the same for all surface elements (only angle of emergent flux differs) • Go from proportional to vsini to independent(save a factor of a few up to > 10)

  9. Non-Magnetic Case • Don’t need: line components, local field, component strengths. (but save almost no time) • Can use non-polarized radiative transfer(relatively small time saving)

  10. Total time saving • Itot 10: 10 surface elements vs 100 1 Voight profile vs. a few 100 (per line, layer, window and phase) • 133 lines (60 Å) in 5 sec vs. 849 sec • Identical non-magnetic results, down to machine precision.

  11. Automated 2 Fitting • Zeeman acts as the fitting function • Preserve compatibility with regular Zeeman (easy upgrades) • Determine vsini, microturbluence, abundances • Possibly T and logg...

  12. Levenberg-Marquardt • Use Levenberg Marquardt fitting algorithm: • Fast • Many parameters • Somewhat non-linear • Still can get stuck in local minima

  13. Fitting results • Conditions: 120 lines, 100 Å, 8 free parameters(vsini, microturbulence, Ca, Ti, V, Cr, Fe, Ba) • 4 iterations, 41 Zeeman calls

  14. Fitting Results

  15. Fitting Results • Repeat this process for several windows • Averages • Standard deviations • Discrepancies • Check result are sensible • Parameters are constrained • Inaccurate atomic data is not a (serious) problem

  16. Adding Temperature • Interpolating on a grid of model atmospheres • Constrain T by excitation potentials • And logg by ionization balance • Test results of throwing everything in • Calculate new abundance specific models, e.g. ATLAS12.

  17. Adding Temperature HD 73666 comparison

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