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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 - PowerPoint PPT Presentation
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A. Lagg – He 10830 lecture NAOJ, Aug 2008A. Lagg – He 10830 lecture NAOJ, Aug 200811
He 10830 lectureHe 10830 lecture:some aspects as seen from an observer‘s viewpoint
Andreas LaggAndreas Lagg
National Astronomical Observatory of JapanNational Astronomical Observatory of Japanandand
Max-Planck-Institut für Sonnensystemforschung,Max-Planck-Institut für Sonnensystemforschung,Katlenburg-Lindau, GermanyKatlenburg-Lindau, Germany
no quantum theoryno quantum theory
no derivation of formulaeno derivation of formulae
no in depth explanation of no in depth explanation of Hanle theoryHanle theory
no solar physicsno solar physics
phenomenological explanation phenomenological explanation of effects (Hanle, PB, atomic of effects (Hanle, PB, atomic polarization)polarization)
application of formulae to application of formulae to demonstrate influence of CI, demonstrate influence of CI, geometry, PB, Hanle on Stokes geometry, PB, Hanle on Stokes IQUVIQUV
A. Lagg – He 10830 lecture NAOJ, Aug 2008A. Lagg – He 10830 lecture NAOJ, Aug 200822
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)Harvey & Sheeley (1977)
A. Lagg – He 10830 lecture NAOJ, Aug 2008A. Lagg – He 10830 lecture NAOJ, Aug 200833
Para / Ortho Helium
Centeno et al., 2008Centeno et al., 2008
A. Lagg – He 10830 lecture NAOJ, Aug 2008A. Lagg – He 10830 lecture NAOJ, Aug 200844
Ionization / Recombination Scheme
Centeno et al., 2008Centeno et al., 2008
A. Lagg – He 10830 lecture NAOJ, Aug 2008A. Lagg – He 10830 lecture NAOJ, Aug 200855
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
A. Lagg – He 10830 lecture NAOJ, Aug 2008A. Lagg – He 10830 lecture NAOJ, Aug 200866
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 5876both 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., 2008Asensio Ramos et al., 2008
A. Lagg – He 10830 lecture NAOJ, Aug 2008A. Lagg – He 10830 lecture NAOJ, Aug 200877
He 10830 – Formation Height
equil.hydrostat.
Tr1
Tr2+3
He
de
ns
ity
3S
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
A. Lagg – He 10830 lecture NAOJ, Aug 2008A. Lagg – He 10830 lecture NAOJ, Aug 200888
Influence of Height above Limb
Centeno et al., 2008Centeno et al., 2008
He 10830 He D3 5876
FAL-C, nominal CI
highest
lowest
A. Lagg – He 10830 lecture NAOJ, Aug 2008A. Lagg – He 10830 lecture NAOJ, Aug 200899
Influence of Coronal Illumination (CI)
Centeno et al., 2008Centeno et al., 2008
change of ratio!(additional diagnostic tool)
He 10830 He D3 5876
A. Lagg – He 10830 lecture NAOJ, Aug 2008A. Lagg – He 10830 lecture NAOJ, Aug 20081010
Zeeman Effect
reliable magnetic field information for B >200 Gsimultaneous observation of photosphere (Si) and chromosphere (He)three (blended) HeI lines("blue" line + 2 "red" lines)
The HeI 10830 diagnostics: Zeeman effectThe HeI 10830 diagnostics: Zeeman effect
Line WL [Å] Transition geff rOS
Si I 10827.088 4s 4s 33PP22 - 4p - 4p 33PP22 1.50
He Ia 10829.091 2s 2s 33SS11 - 2p - 2p 33PP00 2.00 0.11
He Ib 10830.250 2s 2s 33SS11 - 2p - 2p 33PP11 1.75 0.33
He Ic 10830.340 2s 2s 33SS11 - 2p - 2p 33PP22 1.25 0.56
Atomic Parameters: [Lagg et al., 2007]Atomic Parameters: [Lagg et al., 2007]
A. Lagg – He 10830 lecture NAOJ, Aug 2008A. Lagg – He 10830 lecture NAOJ, Aug 20081111
The HeI 10830 diagnostics: Paschen Back effectThe HeI 10830 diagnostics: Paschen Back effect
Paschen-Back Effect
B LS HH Weak B
BLSC HHHH
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 LThe interaction betweenthe external B and the
magnetic moment of the eBLS HH Strong B
Zeeman effectRegime
Paschen-Back effect Regime
B LS HH IPBS Regime
A. Lagg – He 10830 lecture NAOJ, Aug 2008A. Lagg – He 10830 lecture NAOJ, Aug 20081212
The HeI 10830 diagnostics: Paschen Back effectThe HeI 10830 diagnostics: Paschen Back effect
Paschen-Back Effect
Socas-Navarro et al. (2004)Socas-Navarro et al. (2004)
LZS IPBS
Positions and strengths of the Zeeman components as a function of the magnetic
fieldTr 1 Tr 1
Tr 2 Tr 2
Tr 3 Tr 3
Δλ
(Å)
Δλ
(Å)
Δλ
(Å)
rela
tive
str
engt
hre
lati
ve s
tren
gth
rela
tive
str
engt
h
A. Lagg – He 10830 lecture NAOJ, Aug 2008A. Lagg – He 10830 lecture NAOJ, Aug 20081313
Paschen Back Effect: influence on Q, U, V
Sasso et al. (2006)Sasso et al. (2006)
dashed = w/o PBdotted = with PB
A. Lagg – He 10830 lecture NAOJ, Aug 2008A. Lagg – He 10830 lecture NAOJ, Aug 20081414
Paschen-Back effect: Error on parameters
Sasso et al. (2006)Sasso et al. (2006)
A. Lagg – He 10830 lecture NAOJ, Aug 2008A. Lagg – He 10830 lecture NAOJ, Aug 20081515
Hanle Effect (Trujillo-Bueno, 2002, Landi Degl'Innocenti, 1982)(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 effectThe HeI 10830 diagnostics: Hanle effect
A. Lagg – He 10830 lecture NAOJ, Aug 2008A. Lagg – He 10830 lecture NAOJ, Aug 20081616
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
lifeJ tgB /1106
ωL >> 1/tlife
LP in forward scattering: max. polarization along ±y90° scattering: no polarization
ωL ≈ 1/tlife
LP in forward scattering: weaker, but still ±y90° scattering: lin.pol. in Q, U, smaller than in non-magnetic case
The HeI 10830 diagnostics: Hanle + BThe HeI 10830 diagnostics: Hanle + B
Hanle Effect (Trujillo-Bueno, 2002, Landi Degl'Innocenti, 1982)(Trujillo-Bueno, 2002, Landi Degl'Innocenti, 1982)
A. Lagg – He 10830 lecture NAOJ, Aug 2008A. Lagg – He 10830 lecture NAOJ, Aug 20081717
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
A. Lagg – He 10830 lecture NAOJ, Aug 2008A. Lagg – He 10830 lecture NAOJ, Aug 20081818
Hanle Effect, the He 10830 case
He Blue Line (JHe Blue Line (JLL=1, J=1, JUU=0):=0):
degenerate lower leveldegenerate lower levelupper level cannot carry atomic
polarization→ emitted beam to (1) unpolarized→ transmitted beam (2) has excess of linear polarization ┴ to B (=dichroism)
Trujillo-Bueno, 2001Trujillo-Bueno, 2001
'normal‘ (scattering) case:upper level atomic polarization
Transition: JL = 0 → JU = 1
The HeI 10830 diagnostics: Atomic PolarizationThe HeI 10830 diagnostics: Atomic Polarization
A. Lagg – He 10830 lecture NAOJ, Aug 2008A. Lagg – He 10830 lecture NAOJ, Aug 20081919
Hanle Effect, the He 10830 case Trujillo-Bueno, 2001Trujillo-Bueno, 2001
'normal‘ (scattering) case:upper level atomic polarization
Transition: JL = 0 → JU = 1
The HeI 10830 diagnostics: Atomic PolarizationThe HeI 10830 diagnostics: Atomic Polarization
He Red Lines (JHe Red Lines (JLL=1, J=1, JUU=1 or 2):=1 or 2):
degenerate upper & lower leveldegenerate upper & lower levelboth levels carry atomic polarization
→ emitted beam to (1) polarized→ transmitted beam (2) has excess of linear polarization ┴ to B
A. Lagg – He 10830 lecture NAOJ, Aug 2008A. Lagg – He 10830 lecture NAOJ, Aug 20082020
90° scattering: linear polarization only in red line
Trujillo-Bueno, 2001Trujillo-Bueno, 2001
The prominence case
A. Lagg – He 10830 lecture NAOJ, Aug 2008A. Lagg – He 10830 lecture NAOJ, Aug 20082121
forward scattering: linear polarization in red & blue line
Trujillo-Bueno, 2001Trujillo-Bueno, 2001
The filament case
A. Lagg – He 10830 lecture NAOJ, Aug 2008A. Lagg – He 10830 lecture NAOJ, Aug 20082222
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 G
auss
↑↓
> 8
Gau
ss ↓
0 – 8 Gauss 8 - 100 Gauss
A. Lagg – He 10830 lecture NAOJ, Aug 2008A. Lagg – He 10830 lecture NAOJ, Aug 20082323
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 diagramfor:
INC 180-INCandAZI -AZI
andAZI 180-AZI(but: different V)
(traditional ambiguities)
Merenda et al., 2006Merenda et al., 2006
Van Vleck ambiguityVan Vleck ambiguitysaturated regime
A. Lagg – He 10830 lecture NAOJ, Aug 2008A. Lagg – He 10830 lecture NAOJ, Aug 20082424
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., 2006Merenda 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.
A. Lagg – He 10830 lecture NAOJ, Aug 2008A. Lagg – He 10830 lecture NAOJ, Aug 20082525
Dependence of LP on optical thickness of He slab
Asensio Ramos et al., 2008Asensio Ramos et al., 2008
no change in ratio!
A. Lagg – He 10830 lecture NAOJ, Aug 2008A. Lagg – He 10830 lecture NAOJ, Aug 20082626
Dependence of Hanle signal on inclination and observing angle
Asensio Ramos et al., 2008Asensio Ramos et al., 2008
μ=0.1
μ=0.1
μ=1
μ=1
cos2(ΘVV)=1/3
B=10G, h=3”
red
com
p.
blue
com
p.
U/IU/I
Q/I
Q/I
A. Lagg – He 10830 lecture NAOJ, Aug 2008A. Lagg – He 10830 lecture NAOJ, Aug 20082727
Dependence of Stokes Q on magnetic field strength
Trujillo Bueno and Asensio Ramos, 2007Trujillo Bueno and Asensio Ramos, 2007
A. Lagg – He 10830 lecture NAOJ, Aug 2008A. Lagg – He 10830 lecture NAOJ, Aug 20082828
Dependence of Stokes Q on magnetic field strength
Trujillo Bueno and Asensio Ramos, 2007Trujillo Bueno and Asensio Ramos, 2007
A. Lagg – He 10830 lecture NAOJ, Aug 2008A. Lagg – He 10830 lecture NAOJ, Aug 20082929
Dependence of Stokes Q on magnetic field strength
Trujillo Bueno and Asensio Ramos, 2007Trujillo Bueno and Asensio Ramos, 2007
A. Lagg – He 10830 lecture NAOJ, Aug 2008A. Lagg – He 10830 lecture NAOJ, Aug 20083030
Dependence of Stokes Q on magnetic field strength
Trujillo Bueno and Asensio Ramos, 2007Trujillo Bueno and Asensio Ramos, 2007
atomic polarization must not be neglected even for strong fields!
A. Lagg – He 10830 lecture NAOJ, Aug 2008A. Lagg – He 10830 lecture NAOJ, Aug 20083131
Dependence of Stokes Q on magnetic field strength
Trujillo Bueno and Asensio Ramos, 2007Trujillo Bueno and Asensio Ramos, 2007
A. Lagg – He 10830 lecture NAOJ, Aug 2008A. Lagg – He 10830 lecture NAOJ, Aug 20083232
Some pitfalls for Zeeman-used scientists
Zeeman:total linear polarization is proportional to transversal field
disk centerB=500G
blue: INC=54° (more horizontal)green: INC=44°
red: INC=34° (more vertical)
A. Lagg – He 10830 lecture NAOJ, Aug 2008A. Lagg – He 10830 lecture NAOJ, Aug 20083333
Some pitfalls for Zeeman-used scientists
Zeeman:total linear polarization is proportional to transversal field
Hanle:not at all!(van Vleck angle)
disk centerB=50G
blue: INC=54° (more horizontal)green: INC=44°
red: INC=34° (more vertical)
A. Lagg – He 10830 lecture NAOJ, Aug 2008A. Lagg – He 10830 lecture NAOJ, Aug 20083434
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 centerB=50G
blue: INC=54° (more horizontal)green: INC=44°
red: INC=34° (more vertical)
A. Lagg – He 10830 lecture NAOJ, Aug 2008A. Lagg – He 10830 lecture NAOJ, Aug 20083535
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 centerINC=60°
blue: B=100G (strongest)green: B=25G
red: B=1G (weakest)
A. Lagg – He 10830 lecture NAOJ, Aug 2008A. Lagg – He 10830 lecture NAOJ, Aug 20083636
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 kG10-3 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 Baveraging: 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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