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He 10830 lecture : some aspects as seen from an observer‘s viewpoint

He 10830 lecture : some aspects as seen from an observer‘s viewpoint. Andreas Lag g National Astronomical Observatory of Japan and Max-Planck-Institut für Sonnensystemforschung, Katlenburg-Lindau, Germany. no quantum theory no derivation of formulae no in depth explanation of Hanle theory

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He 10830 lecture : some aspects as seen from an observer‘s viewpoint

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  1. He 10830 lecture:some aspects as seen from an observer‘s viewpoint Andreas Lagg National Astronomical Observatory of Japanand Max-Planck-Institut für Sonnensystemforschung,Katlenburg-Lindau, Germany no quantum theory no derivation of formulae no in depth explanation of Hanle theory no solar physics phenomenological explanation of effects (Hanle, PB, atomic polarization) application of formulae to demonstrate influence of CI, geometry, PB, Hanle on Stokes IQUV

  2. He 10830 - History first solar obs. in He 10830:D‘Azambuja (1938), Zirin (1956), Mohler & Goldberg (1956), Namba (1963), Fisher (1964), Milkey et al. (1973) Harvey & Hall (1971) Giovanelli & Hall (1977) Lites et al. (1985): report on steady flows (9 km/s, hours to days) Avrett (1994): formation of He 10830 He 10830 spectropolarimetry:Lin (1995), Lin et al. 1996, 1998 Trujillo-Bueno (2002): atomic polarization in He 10830 solved Giovanelli & Hall (1977) Harvey & Sheeley (1977)

  3. Para / Ortho Helium Centeno et al., 2008

  4. Ionization / Recombination Scheme Centeno et al., 2008

  5. The He 10830 Triplet Transition 23S1 – 23P2,1,0 absorption depends on: density and extend of upper chromosphere coronal radiation in the λ<504 Å continuum 2s 3S level populated by recombination of He II orcollisional excitation from 11S Tr1: 10829.0911 Å, f=0.1111, geff=2.00 Tr2: 10830.2501 Å, f=0.3333, geff=1.75 Tr3: 10830.3397 Å, f=0.5556, geff=1.25

  6. The He D3 line Transition 23P2,1,0 - 33D3,2,1 formation mechanism similar to He 10830 (CI required) difference to 10830: optical thickness of the observed solar plasma structures is weaker on the solar disk it is much easier to see structures in 10830 than in 5876 both lines are clearly seen in emission when observing offlimb structures such as prominences and spicules. He 10830 preferable because: forward scattering creates measurable linear polarization signals in the lines of the He I 10830 when the magnetic field is inclined (Trujillo Bueno et al. 2002) nearby presence of Si I line  coupling science Asensio Ramos et al., 2008

  7. He 10830 – Formation Height He density 3S1 z  • model atmospheres: • T-profile pressure • models A (cell-center), C (average), F (bright network), P (plage) • CH/CL hi/lo coronal irradiance Tr1 Tr2+3 WL  Avrett et al. (1994)

  8. Influence of Height above Limb He 10830 He D3 5876 lowest highest FAL-C, nominal CI Centeno et al., 2008

  9. Influence of Coronal Illumination (CI) change of ratio!(additional diagnostic tool) He 10830 He D3 5876 Centeno et al., 2008

  10. The HeI 10830 diagnostics: Zeeman effect Zeeman Effect reliable magnetic field information for B >200 G simultaneous observation of photosphere (Si) and chromosphere (He) three (blended) HeI lines("blue" line + 2 "red" lines) Atomic Parameters: [Lagg et al., 2007]

  11. The HeI 10830 diagnostics: Paschen Back effect Weak B Strong B Paschen-Back Effect The Hamiltonian of an electron in an atom in an external uniform magnetic field: Zeeman effect Regime Hamiltonian of the electron affected by the Coulomb interaction Coupling between S and L The interaction between the external B and the magnetic moment of the e Paschen-Back effect Regime IPBS Regime

  12. The HeI 10830 diagnostics: Paschen Back effect LZS IPBS Tr 1 Tr 1 relative strength Δλ (Å) Tr 2 Tr 2 Δλ (Å) relative strength Tr 3 Tr 3 Δλ (Å) relative strength Paschen-Back Effect Positions and strengths of the Zeeman components as a function of the magnetic field Socas-Navarro et al. (2004)

  13. Paschen Back Effect: influence on Q, U, V Sasso et al. (2006) dashed = w/o PBdotted = with PB

  14. Paschen-Back effect: Error on parameters Sasso et al. (2006)

  15. The HeI 10830 diagnostics: Hanle effect Hanle Effect (Trujillo-Bueno, 2002, Landi Degl'Innocenti, 1982) non magnetic case: • anisotropic illumination of atoms (3 independent, damped oscillators in x,y,z) with unpolarized light • no polarization in forward scattering • complete linear polarization in 90° scattering Hanle effect:modification of (atomic) polarization caused by the action of a magnetic field

  16. The HeI 10830 diagnostics: Hanle + B Hanle Effect (Trujillo-Bueno, 2002, Landi Degl'Innocenti, 1982) magnetic case: now the 3 oscillators are not independent: 1 osc. along B (ω0) 2 osc. around B(ω0-ωL ; ω0+ωL) damped oscillation precesses around B→ rosette like pattern→ damping time tlife = 1/γ ωL≈ 1/tlife LP in forward scattering: weaker, but still ±y 90° scattering: lin.pol. in Q, U, smaller than in non-magnetic case ωL >> 1/tlife LP in forward scattering: max. polarization along ±y 90° scattering: no polarization

  17. Atomic Polarization: the quantum picture 'normal‘ (scattering) case:upper level atomic polarization polarization only in emission (90° scattering) no polarization in absorption (forward scattering) Transition: JL = 0 → JU = 1

  18. The HeI 10830 diagnostics: Atomic Polarization Hanle Effect, the He 10830 case Trujillo-Bueno, 2001 'normal‘ (scattering) case:upper level atomic polarization Transition: JL = 0 → JU = 1 He Blue Line (JL=1, JU=0):degenerate lower level upper level cannot carry atomic polarization → emitted beam to (1) unpolarized → transmitted beam (2) has excess of linear polarization ┴ to B (=dichroism)

  19. The HeI 10830 diagnostics: Atomic Polarization Hanle Effect, the He 10830 case Trujillo-Bueno, 2001 'normal‘ (scattering) case:upper level atomic polarization Transition: JL = 0 → JU = 1 He Red Lines (JL=1, JU=1 or 2):degenerate upper & lower level both levels carry atomic polarization → emitted beam to (1) polarized → transmitted beam (2) has excess of linear polarization ┴ to B

  20. The prominence case • 90° scattering: • linear polarization only in red line Trujillo-Bueno, 2001

  21. The filament case • forward scattering: • linear polarization in red & blue line Trujillo-Bueno, 2001

  22. Hanle effect saturation Hanle effect sensitive linear polarization signal depends on magnetic field strength magnetic field direction (around B = 10−2 G, the density matrix elements start to be affected by the magnetic field caused by a feedback effect that the alteration of the lower-level polarization has on the upper levels) ↑ < 8 Gauss ↑↓ > 8 Gauss ↓ Hanle saturation regime • linear polarization signal depends on • magnetic field direction (coherences are negligible and the atomic alignment values of the lower and upper levels are insensitive to the strength of the magnetic field) Application:disk center, horizontal field:tan(2*AZI) = Q/U 0 – 8 Gauss 8 - 100 Gauss

  23. Ambiguities of Hanle effect Van Vleck ambiguity solid lines: INC=const, AZI=(-90,90)dashed lines: AZI=±90, INC=(0,-90)B=25 Gauss, off-limb, red comp. polarization diagram: same QU diagram for: INC  180-INCandAZI  -AZI and AZI  180-AZI(but: different V) (traditional ambiguities) saturated regime Merenda et al., 2006

  24. Ambiguities: van Vleck ambiguity + traditional ambiguity Merenda et al., 2006 INC=80°, AZI=-46°, B=22G or INC=40°, AZI=19°, B=25G plus traditional 180° ambiguity:INC=100°, AZI=46°, B=22G or INC=140°, AZI=-19°, B=25G The Van Vleck ambiguity occurs only for some combinations of the inclinations and azimuths. Moreover, it occurs mainly in the saturation regime of the Hanle effect.

  25. Dependence of LP on optical thickness of He slab Asensio Ramos et al., 2008  no change in ratio!

  26. Dependence of Hanle signal on inclination and observing angle B=10G, h=3” Q/I μ=1 μ=1 Q/I blue comp. cos2(ΘVV)=1/3 μ=0.1 red comp. U/I U/I μ=0.1 Asensio Ramos et al., 2008

  27. Dependence of Stokes Q on magnetic field strength Trujillo Bueno and Asensio Ramos, 2007

  28. Dependence of Stokes Q on magnetic field strength Trujillo Bueno and Asensio Ramos, 2007

  29. Dependence of Stokes Q on magnetic field strength Trujillo Bueno and Asensio Ramos, 2007

  30. Dependence of Stokes Q on magnetic field strength Trujillo Bueno and Asensio Ramos, 2007 atomic polarization must not be neglected even for strong fields!

  31. Dependence of Stokes Q on magnetic field strength Trujillo Bueno and Asensio Ramos, 2007

  32. Some pitfalls for Zeeman-used scientists Zeeman:total linear polarization is proportional to transversal field blue: INC=54° (more horizontal)green: INC=44°red: INC=34° (more vertical) disk centerB=500G

  33. Some pitfalls for Zeeman-used scientists Zeeman:total linear polarization is proportional to transversal field Hanle:not at all!(van Vleck angle) blue: INC=54° (more horizontal)green: INC=44°red: INC=34° (more vertical) disk centerB=50G

  34. Some pitfalls for Zeeman-used scientists Zeeman:ratio between linear and circular polarization is proportional to inlination Hanle:not at all!(van Vleck angle)(same example) blue: INC=54° (more horizontal)green: INC=44°red: INC=34° (more vertical) disk centerB=50G

  35. Some pitfalls for Zeeman-used scientists Zeeman:strength of polarization signal is a measure of strength of magnetic field Hanle:not for very weak fields!(Hanle depolarizes) saturation regime (10-100G):strength of linear polarization does not depend on B blue: B=100G (strongest)green: B=25Gred: B=1G (weakest) disk centerINC=60°

  36. Conclusions Strong fields (active region, plage fields): • reliable measurements for B > 200 G (100 G for special geometries) • Paschen-Back effect important for correct determination of |B| • atomic polarization important for B < 1.5 kG • 10-3 polarization signal sufficient Weak fields: • 10 – 100 G: saturated Hanle regime: LP determined by direction of B • <10 G: Hanle sensitive regime: LP depends on direction and on strength of B • averaging: weak fields do not cancel out! • good: 4x10-4 polarization signal, ideal: 1x10-4 Hanle: additional complications in analysis of data • Ambiguities: • 180° Hanle ambiguity • Van Vleck ambiguity • Computation: • x10-100 as compared to Zeeman only

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