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Multi-Height Full Stokes Polarimetry of a B-Class Flare

Multi-Height Full Stokes Polarimetry of a B-Class Flare. Tom Schad – in collaboration with – Ali Tritschler & Matt Penn. CANFIELD-FEST. Aug 8 – 11, 2010. Introduction. The Problem:. How do flares acquire and release free magnetic energy into thermal and nonthermal energy?.

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Multi-Height Full Stokes Polarimetry of a B-Class Flare

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  1. Multi-Height Full Stokes Polarimetry of a B-Class Flare Tom Schad – in collaboration with – Ali Tritschler & Matt Penn CANFIELD-FEST Aug 8 – 11, 2010

  2. Introduction The Problem: • How do flares acquire and release free magnetic energy into thermal and nonthermal energy? • Constraining the Problem: • Quantifying the transfer of energy…usual methods: • multi-spectral diagnostics • energetic particle spectrum measurement (@ 1 AU) • Evaluating magnetic field topology from photospheric field. Image courtesy A.O. Benz, “Flare Observations” Living Rev. Solar Phys. 5 This talk  A not-as-usual method  chromospheric polarimetry of flaring regions Tom Schad - Canfield-Fest

  3. A few previous studies… • Hénoux & Semel, 1981 • Penn & Kuhn 1995 • Metcalf, Leka, & Mickey 2005 • Xu et al. 2006, 2007 • Sasso et al. 2007 • Firstova et al. 2008 Achieving polarimetric signals from the chromosphere is observationally and as well as theoretically challenging. Tom Schad - Canfield-Fest

  4. Why Multi-Height Flare Polarimetry? Field Topology Advantage ‘Actual?’ force free boundary for extrapolation Field Reconstruction Assumed Non-Linear Force-Free Photospheric Field Extrapolation Chromospheric Zeeman Polarimetry More accurate topology for examining of flaring region skeleton Direct measure of total field energy Probe of not-well classified horizontal fine structure in chromosphere..perhaps flaring role Accelerated Particle Dist. Measure Measure of accelerated particle anisotropy in solar atmosphere. Measuring spectra of accelerated particles (1 AU) Impact Linear Polarization Tom Schad - Canfield-Fest

  5. CHALLENGES Line Formation Complex NLTE formation Weak polarization Large range of contribution heights -Photospheric contamination Necessary Observations Interesting fields largely horizontal Fine scale structure Large scale features [+large Grad(VLOS)] Short scale dynamics Technical Needs Multi-wavelength spectropolarimetry, large field of view, high cadence, diffraction-limited, high spectral resolution, high polarization accuracy, Tom Schad - Canfield-Fest

  6. He I Triplet @10830 - promising diagnostic of vector magnetic fields in upper chromosphere Observational Magnetic Field Reconstructions NLFF Extrapolation Coupled Zeeman, Hanle, Atomic Polarization, PB effect inversions possible HELIX+ and HAZEL codes available Solanki et al., 2003, 2004 Tom Schad - Canfield-Fest

  7. Observations@ the Dunn Solar Telescope, May 2010 • FIRS • Fe I 6302, Si 10827, He I 10830 – Full Stokes Polarimetry • IBIS • Ca II 8542 – Full Stokes • Whitelight Imaging • + G-Band Imaging • + DST High Order Adaptive Optics • + Supporting Observations @ SOLIS (10830 spectroheliograms & 8542 L)and McMath/Pierce (10830 – Full Stokes) Tom Schad - Canfield-Fest

  8. Slit 2 Slit 3 Slit 4 Slit 1 FIRSThe Facility Infrared Spectropolarimeter at the Dunn Solar Telescope Sunspot in Slit 2 Two Beams Fe I 630.1 nm Fe I 630.2 nm Raw VIS Frame – 630 nm Si I 1082.7 nm • Multi-Spectral Diff.Limited Slit-Spectropolarimeter • Simultaneous IR & Vis Full Stokes Polarimetry • Multi-Slit (Fast scanning of solar image across slit unit) • Large Field of View (up to ~ 170” x 70”) • Currently operates in 630, 1565, and 1083 nm spectral windows Two Beams Telluric Jaeggli et al. (2008) He I 1083 nm Triplet Raw IR Frame – 1083 nm

  9. IBIS The InterferometricBidimensionalSpectro(polari)meter • Builds 3(or 4) dim data cubes [X, Y, LAMBDA, (STOKES STATE)] using tunable scanning of a given spectral window or combinations of spectral windows • Usable Range: 5800 Å - 8600 Å • High Spectral ( R≥ 200 000), spatial ( ≃ 0.2″), and temporal resolution (several frames per second) Raw IBIS Frame with Dual-Beam Polarimetry FOV ~ 40” X 80” Cavallini (2006); Reardon & Cavallini (2008) Tom Schad - Canfield-Fest

  10. May 25, 2010 Operations IBIS FIRS • Ca II λ8542 Å • Full Stokes Dual-Beam Polarimetry • 20 spectral points (Stokes definition modulation sequence at each wavelength + simultaneous whitelight continuum frames) • 36 second period for all 120 [i.e. 20-λ x 6-states] measurements • Near continuous scanning between 13:00 and 18:00 UT • Unbinned Polarimetry RMS noise ~ 1x10-2 IC • Visible Arm: Fe λ 6301 Å and λ 6302 Å (1 pm spectral disp) • Infrared Arm: Si λ 10827 Å and He I λ 10830 Å (3.8 pm spectral disp) • Full Stokes Dual-Beam Polarimetry • 4-slit unit used • FOV ~168” x 70” • Deeper integration scan (1 hour for full FOV scan…FOV can be scan ~ 20 min) • Angular resolution: 0.29” • RMS noise @ 029” res ~ 2x10-3 IC Tom Schad - Canfield-Fest

  11. OBSERVING TARGET NOAA AR 11072 May 25, 2010 μ ≈ 0.6 S15 °, W35° FIRS FOV IBIS FOV FIRS slit aligned perpendicular to Earth’s Horizon (reason for FOV rotation between scans) Tom Schad - Canfield-Fest

  12. A B6.5 Flare on May 25, 2010 H-alpha movie From BBSO Full Disk Images Tom Schad - Canfield-Fest

  13. The Observed Flare - Context • Put in continuum int map, hewid equivalent width map, IBIS frame (c.int + lcen), & BBSO flare map Tom Schad - Canfield-Fest

  14. First, a photometric/spectroscopic look: H alpha and Ca II 8542 intensity follows closely the X-ray flare flux. GOES X-ray Flux IBIS 8542 Line Center Intensity Movie Tom Schad - Canfield-Fest

  15. He I 10830 Flare Response 13:05:39 UT • In large flares, 10830 emission common. • Emission seen in small flares, but spatial extent is often limited. • Formation of 10830 flare emission not well known [You et al. 2001] • Most likely enhanced coronal EUV deepens some spectra during event. 14:15:24 UT 15:20:29 UT Primary formation processes [Avrett et al. 1994; Ding et al. 2005]: 16:25:59 UT Photoionization-Recombination (PRM) – due to coronal EUV Collisional excitation Collision ionization (CM)  Hard to distinguish. FIRS Observations Tom Schad - Canfield-Fest

  16. He I 10830 – Red Line Intensity He I 10830 – Blue Line Intensity Continuum Intensity Near Si I 10827 Tom Schad - Canfield-Fest

  17. A Possible Nonthermal Effect to He I 10830 Line Formation Ding et al. (2005) suggest a nonthermal electron beam may deepen absorption prior to flare heating excited 10830 emission Slit #3 Flare Light Curve Tom Schad - Canfield-Fest

  18. Quick note on velocity diagnostics Deepened 10830 absoption in contrast to 8542, 6563, etc., allows for better velocity determination. Tom Schad - Canfield-Fest

  19. Flare Polarization Observations…. Magnetic Energy Injection at Flare Location • Flare location association with large magnetic shear along neutral line [Hagyard et al. 1990] • Injection of energy into corona derived from displacement of magnetic features (emergence/cancellation, MMFs, sunspot rotation [Regnier & Canfield 2006]) • Injected energy can be estimated from transverse field motions [Kusano et al. 2002]: Hagyard et al. 1990 Tom Schad - Canfield-Fest

  20. TEMPORAL EVOLUTION OF PHOTOSPHERIC FIELD VECTOR 13:05:39 UT FIRS Scan Start Times 14:15:24 UT 15:20:29 UT Significant Transverse Field 16:25:59 UT FLARE START: 15:46 UT Horizontal Motion of Magnetic Field Tom Schad - Canfield-Fest

  21. Photosphere/Chromosphere Field Comparison 13:05:39 UT 14:15:24 UT Chromospheric Vertical Field More Diffuse 15:20:29 UT 16:25:59 UT Field more ‘pinched’ in chromosphere? Tom Schad - Canfield-Fest

  22. Chromospheric Magnetic and Velocity Structure 13:05:39 UT 14:15:24 UT 15:20:29 UT 16:25:59 UT Tom Schad - Canfield-Fest

  23. Chromospheric Magnetic and Velocity Structure 13:05:39 UT 14:15:24 UT 15:20:29 UT BSE? 16:25:59 UT 9 August 2010 Tom Schad - Canfield-Fest Tom Schad - Canfield-Fest 23

  24. Finally, a look at the full Stokes Spectra…Flare 10830 Emission Stokes Spectra Flare • Only a preliminary look, as reduction needs work. 10830 in emission Curious Stokes V signal in flare.  Red component < noise  Blue comp. shows Zeeman profile. Perhaps optical thickness difference? As seen in Stokes V map, flare location near polarity reversal Hint of Stokes U structure Tom Schad - Canfield-Fest

  25. IBIS 8542 Stokes Vector Movies Complete polarization calibration (unfortunately poor MPEG quality) Tom Schad - Canfield-Fest

  26. 8542 PreFlare vs . Flare Emission Stokes Spectra • Flare fibrils show distinct 8542 emission • Stokes I U crosstalk, but clear but complext changes in Q, U Tom Schad - Canfield-Fest

  27. 8542 Stokes Vector Time Series Flare End 15:55 Flare Peak 15:51 Flare Start 15:46 Anti-symmetric Stokes V profile turned anomalous by flare? Stokes U amplitude seems to increase during flare? What could explain it? Tom Schad - Canfield-Fest

  28. A few possible causes…. • Impact Polarization • Formation Height Change? • Field Topology Shift? • Not real? Instrumental, seeing cross-talk? Effect of limited spectral resolution? Temporal effect? [Firstova et al. 2008] Tom Schad - Canfield-Fest

  29. Concluding Remarks • FIRS and IBIS join observations offer beneficial new diagnostics and instrumental opportunities for flare studies. • He I 10830 triplet could be an important tool for field topology and evolution assessment. • Polarization signatures within flare for 10830 and 8542 shows interesting complex behavior. • Stay tuned… Thank You Tom Schad - Canfield-Fest

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