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A. Lagg – He 10830 lecture NAOJ, Aug 2008 1 He 10830 lecture He 10830 lecture : some aspects as seen from an observer‘s viewpoint Andreas Lagg National.

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Presentation on theme: "A. Lagg – He 10830 lecture NAOJ, Aug 2008 1 He 10830 lecture He 10830 lecture : some aspects as seen from an observer‘s viewpoint Andreas Lagg National."— Presentation transcript:

1 A. Lagg – He 10830 lecture NAOJ, Aug 2008 1 He 10830 lecture He 10830 lecture : some aspects as seen from an observer‘s viewpoint Andreas Lagg 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 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 A. Lagg – He 10830 lecture NAOJ, Aug 2008 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 A. Lagg – He 10830 lecture NAOJ, Aug 2008 3 Para / Ortho Helium Centeno et al., 2008

4 A. Lagg – He 10830 lecture NAOJ, Aug 2008 4 Ionization / Recombination Scheme Centeno et al., 2008

5 A. Lagg – He 10830 lecture NAOJ, Aug 2008 5 The He 10830 Triplet Transition 2 3 S 1 – 2 3 P 2,1,0 absorption depends on: density and extend of upper chromosphere coronal radiation in the λ<504 Å continuum 2s 3 S level populated by recombination of He II or collisional excitation from 1 1 S Tr1: 10829.0911 Å, f=0.1111, g eff =2.00 Tr2: 10830.2501 Å, f=0.3333, g eff =1.75 Tr3: 10830.3397 Å, f=0.5556, g eff =1.25

6 A. Lagg – He 10830 lecture NAOJ, Aug 2008 6 The He D3 line Transition 2 3 P 2,1,0 - 3 3 D 3,2,1 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 A. Lagg – He 10830 lecture NAOJ, Aug 2008 7 He 10830 – Formation Height Tr1 Tr2+3 He density 3 S 1 WL  z  Avrett et al. (1994) model atmospheres:  T-profile pressure  models A (cell-center), C (average), F (bright network), P (plage)  CH/CL hi/lo coronal irradiance

8 A. Lagg – He 10830 lecture NAOJ, Aug 2008 8 Influence of Height above Limb Centeno et al., 2008 He 10830He D 3 5876 FAL-C, nominal CI highest lowest

9 A. Lagg – He 10830 lecture NAOJ, Aug 2008 9 Influence of Coronal Illumination (CI) Centeno et al., 2008 change of ratio! (additional diagnostic tool) He 10830He D 3 5876

10 A. Lagg – He 10830 lecture NAOJ, Aug 2008 10 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) The HeI 10830 diagnostics: Zeeman effect LineWL [Å]TransitiongeffrOS Si I10827.088 4s 3 P 2 - 4p 3 P 2 1.50 He Ia10829.091 2s 3 S 1 - 2p 3 P 0 2.000.11 He Ib10830.250 2s 3 S 1 - 2p 3 P 1 1.750.33 He Ic10830.340 2s 3 S 1 - 2p 3 P 2 1.250.56 Atomic Parameters: [Lagg et al., 2007]

11 A. Lagg – He 10830 lecture NAOJ, Aug 2008 11 The HeI 10830 diagnostics: Paschen Back effect Paschen-Back Effect Weak B The Hamiltonian of an electron in an atom in an external uniform magnetic field: 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 Strong B Zeeman effect Regime Paschen-Back effect Regime IPBS Regime

12 A. Lagg – He 10830 lecture NAOJ, Aug 2008 12 The HeI 10830 diagnostics: Paschen Back effect Paschen-Back Effect Socas-Navarro et al. (2004) LZS IPBS Positions and strengths of the Zeeman components as a function of the magnetic field Tr 1 Tr 2 Tr 3 Δλ (Å) relative strength

13 A. Lagg – He 10830 lecture NAOJ, Aug 2008 13 Paschen Back Effect: influence on Q, U, V Sasso et al. (2006) dashed = w/o PB dotted = with PB

14 A. Lagg – He 10830 lecture NAOJ, Aug 2008 14 Paschen-Back effect: Error on parameters Sasso et al. (2006)

15 A. Lagg – He 10830 lecture NAOJ, Aug 2008 15 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 The HeI 10830 diagnostics: Hanle effect

16 A. Lagg – He 10830 lecture NAOJ, Aug 2008 16 magnetic case: now the 3 oscillators are not independent: 1 osc. along B (ω 0 ) 2 osc. around B (ω 0 -ω L ; ω 0 +ω L ) damped oscillation precesses around B → rosette like pattern → damping time tlife = 1/γ ω L >> 1/t life LP in forward scattering: max. polarization along ±y 90° scattering: no polarization ω L ≈ 1/t life LP in forward scattering: weaker, but still ±y 90° scattering: lin.pol. in Q, U, smaller than in non-magnetic case The HeI 10830 diagnostics: Hanle + B Hanle Effect (Trujillo-Bueno, 2002, Landi Degl'Innocenti, 1982)

17 A. Lagg – He 10830 lecture NAOJ, Aug 2008 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 A. Lagg – He 10830 lecture NAOJ, Aug 2008 18 Hanle Effect, the He 10830 case He Blue Line (J L =1, J U =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) Trujillo-Bueno, 2001 'normal‘ (scattering) case: upper level atomic polarization Transition: JL = 0 → JU = 1 The HeI 10830 diagnostics: Atomic Polarization

19 A. Lagg – He 10830 lecture NAOJ, Aug 2008 19 Hanle Effect, the He 10830 case Trujillo-Bueno, 2001 'normal‘ (scattering) case: upper level atomic polarization Transition: JL = 0 → JU = 1 The HeI 10830 diagnostics: Atomic Polarization He Red Lines (J L =1, J U =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 A. Lagg – He 10830 lecture NAOJ, Aug 2008 20 90° scattering:  linear polarization only in red line Trujillo-Bueno, 2001 The prominence case

21 A. Lagg – He 10830 lecture NAOJ, Aug 2008 21 forward scattering:  linear polarization in red & blue line Trujillo-Bueno, 2001 The filament case

22 A. Lagg – He 10830 lecture NAOJ, Aug 2008 22 Hanle effect saturation Hanle effect sensitive linear polarization signal depends on 1)magnetic field strength 2)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) Hanle saturation regime linear polarization signal depends on 1)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 ↑ 8 Gauss ↓ 0 – 8 Gauss8 - 100 Gauss

23 A. Lagg – He 10830 lecture NAOJ, Aug 2008 23 Ambiguities of Hanle effect 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-INC and AZI  -AZI and AZI  180-AZI (but: different V) (traditional ambiguities) Merenda et al., 2006 Van Vleck ambiguity saturated regime

24 A. Lagg – He 10830 lecture NAOJ, Aug 2008 24 Ambiguities: van Vleck ambiguity + traditional ambiguity 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 Merenda et al., 2006 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 A. Lagg – He 10830 lecture NAOJ, Aug 2008 25 Dependence of LP on optical thickness of He slab Asensio Ramos et al., 2008  no change in ratio!

26 A. Lagg – He 10830 lecture NAOJ, Aug 2008 26 Dependence of Hanle signal on inclination and observing angle Asensio Ramos et al., 2008 μ=0.1 μ=1 cos 2 (Θ VV )=1/3 B=10G, h=3” red comp. blue comp. U/I Q/I

27 A. Lagg – He 10830 lecture NAOJ, Aug 2008 27 Dependence of Stokes Q on magnetic field strength Trujillo Bueno and Asensio Ramos, 2007

28 A. Lagg – He 10830 lecture NAOJ, Aug 2008 28 Dependence of Stokes Q on magnetic field strength Trujillo Bueno and Asensio Ramos, 2007

29 A. Lagg – He 10830 lecture NAOJ, Aug 2008 29 Dependence of Stokes Q on magnetic field strength Trujillo Bueno and Asensio Ramos, 2007

30 A. Lagg – He 10830 lecture NAOJ, Aug 2008 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 A. Lagg – He 10830 lecture NAOJ, Aug 2008 31 Dependence of Stokes Q on magnetic field strength Trujillo Bueno and Asensio Ramos, 2007

32 A. Lagg – He 10830 lecture NAOJ, Aug 2008 32 Some pitfalls for Zeeman-used scientists Zeeman: total linear polarization is proportional to transversal field disk center B=500G blue: INC=54° (more horizontal) green: INC=44° red: INC=34° (more vertical)

33 A. Lagg – He 10830 lecture NAOJ, Aug 2008 33 Some pitfalls for Zeeman-used scientists Zeeman: total linear polarization is proportional to transversal field Hanle: not at all! (van Vleck angle) disk center B=50G blue: INC=54° (more horizontal) green: INC=44° red: INC=34° (more vertical)

34 A. Lagg – He 10830 lecture NAOJ, Aug 2008 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) disk center B=50G blue: INC=54° (more horizontal) green: INC=44° red: INC=34° (more vertical)

35 A. Lagg – He 10830 lecture NAOJ, Aug 2008 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 disk center INC=60° blue: B=100G (strongest) green: B=25G red: B=1G (weakest)

36 A. Lagg – He 10830 lecture NAOJ, Aug 2008 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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