Presentation is loading. Please wait.

Presentation is loading. Please wait.

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.

Similar presentations


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 lecture NAOJ, Aug He lecture He 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 lecture NAOJ, Aug He 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 He spectropolarimetry: Lin (1995), Lin et al. 1996, 1998 Trujillo-Bueno (2002): atomic polarization in He solved Giovanelli & Hall (1977) Harvey & Sheeley (1977)

3 A. Lagg – He lecture NAOJ, Aug Para / Ortho Helium Centeno et al., 2008

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

5 A. Lagg – He lecture NAOJ, Aug The He 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: Å, f=0.1111, g eff =2.00 Tr2: Å, f=0.3333, g eff =1.75 Tr3: Å, f=0.5556, g eff =1.25

6 A. Lagg – He lecture NAOJ, Aug The He D3 line Transition 2 3 P 2,1, D 3,2,1 formation mechanism similar to He (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 than in 5876 both lines are clearly seen in emission when observing offlimb structures such as prominences and spicules. He preferable because: forward scattering creates measurable linear polarization signals in the lines of the He I 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 lecture NAOJ, Aug He – 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 lecture NAOJ, Aug Influence of Height above Limb Centeno et al., 2008 He 10830He D FAL-C, nominal CI highest lowest

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

10 A. Lagg – He lecture NAOJ, Aug 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 diagnostics: Zeeman effect LineWL [Å]TransitiongeffrOS Si I s 3 P 2 - 4p 3 P He Ia s 3 S 1 - 2p 3 P He Ib s 3 S 1 - 2p 3 P He Ic s 3 S 1 - 2p 3 P Atomic Parameters: [Lagg et al., 2007]

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

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

15 A. Lagg – He lecture NAOJ, Aug 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 diagnostics: Hanle effect

16 A. Lagg – He lecture NAOJ, Aug 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 diagnostics: Hanle + B Hanle Effect (Trujillo-Bueno, 2002, Landi Degl'Innocenti, 1982)

17 A. Lagg – He lecture NAOJ, Aug 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 lecture NAOJ, Aug Hanle Effect, the He 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 diagnostics: Atomic Polarization

19 A. Lagg – He lecture NAOJ, Aug Hanle Effect, the He case Trujillo-Bueno, 2001 'normal‘ (scattering) case: upper level atomic polarization Transition: JL = 0 → JU = 1 The HeI 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 lecture NAOJ, Aug ° scattering:  linear polarization only in red line Trujillo-Bueno, 2001 The prominence case

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

22 A. Lagg – He lecture NAOJ, Aug 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 Gauss Gauss

23 A. Lagg – He lecture NAOJ, Aug 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 lecture NAOJ, Aug 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 lecture NAOJ, Aug Dependence of LP on optical thickness of He slab Asensio Ramos et al., 2008  no change in ratio!

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

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

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

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

32 A. Lagg – He lecture NAOJ, Aug 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 lecture NAOJ, Aug 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 lecture NAOJ, Aug 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 lecture NAOJ, Aug 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 lecture NAOJ, Aug 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 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:  x as compared to Zeeman only


Download ppt "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."

Similar presentations


Ads by Google