Polarized Radiation Diagnostics Methods for “Measuring”
Chromospheric and Coronal Magnetic Fields
Javier Trujillo Bueno(IAC, Tenerife, Spain)

Courtesy of J. Harvey

Solar Chromosphere

Q>0

TRACE image
Here, between the thin solar photosphere and themillion-degree corona dominance of the physics passes
from hydrodynamic to magnetic forces ...

Solar Corona

Outline of the talk
• Itroduction• Physical mechanisms that produce
polarization in spectral lines.
• Some diagnostic methods based on them.
• Some suggestions for SOLAR-C• Concluding comments.
Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

Introduction• Probably, the greatest future challenge in spaceastrophysics is the empirical investigation of
the magnetic field vector in a variety ofastrophysical systems:• Solar outer atmosphere:

Chromoshere, TR and Corona• Circumstellar envelopes• Accreting systems• Etc…

Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)• To this end we need to carry out

spectropolarimetric observations
from space telescopes,
throughout the whole electromagnetic
spectrum, also in the

UV, EUV and X-ray spectral regions.
Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)• The polarization signals I am going to consider here areproduced by the joint action of the Hanle and Zeeman
effects, but I will emphasize here the diagnostic potentialof the spectral line polarization caused byatomic level polarization• Such polarization signals are sensitive to magnetic fields
in a parameter domain that goes from at least one
microgauss to a few hundreds of gauss (Hanle effect).
• Observations of these polarization effects provide

key information, impossible to obtain via conventional
spectropolarimetry.

Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

Physical mechanisms that control thepolarization of the spectral lines thatoriginate in a stellar atmosphere:• The Zeeman effect• Atomic level polarization• The Hanle effectJavier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

What is the Zeeman effect polarization ?

Mr. Zeeman

The spectral line polarization produced by the

wavelength shifts between the sigma and picomponents. (NOTE: such wavelength shifts are due to the
Zeeman splitting of the energy levels).
NOTE: Typically, 100 G or more are needed to observe this effect in
the linear polarization profiles of solar spectral lines (i.e., in the Q/I
Javier Trujillo Bueno (IAC; Tenerife; Spain)
and/or U/I profiles).

Talk at Solar-C science definition meeting (Tokyo, 2008)

Observation of the polarization of the Zeeman effectin sunspots with HINODE

Courtesy of L. Bellot Rubio

Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

Observation of the magnetic fields of the “quiet” solar
photosphere through the “Zeeman eyes” of HINODE(From Lites et al. 2008)

The “skin” of the Sun: the solar photosphere

Spectrograph’s slit

Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

The chromospheric K-line of CA IIOBSERVED IN A SUNSPOT = strongly magnetized region

Linear polarization
created by the
TRANSVERSEZEEMAN effectCircularpolarization createdby the LONGITUDINALZEEMAN effectObservation by Stenflo (2006) with ZIMPOL @ Kitt Peak

Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

The longitudinal Zeeman effect in the 8542 chromospheric line of Ca II±15 G

NSO/SOLIS observation by J. Harvey

Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

GOOD NEWS for the ZEEMAN effect:
The mere detection of polarization implies
the presence of a magnetic field B.
BAD NEWS for the ZEEMAN effect:(1) It is of limited practical interest for the“measurement” of B in chromospheric andcoronal plasmas because the Zeeman polarization scaleswith the ratio between the Zeeman splitting and the
Doppler-broadened line width.
(2) The Zeeman effect is BLIND to B that are tangled
on scales too small to be resolved.
Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

What is the Hanle effect ?

Mr. Hanle

Any modification of the atomic level polarization(population imbalances and coherences) due to the presence ofa magnetic field.
NOTE: Typically, Q/I and U/I are sensitive to magnetic fields
with strengths between at least 1 milligauss and 100 G !
Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

ATOMIC LEVEL POLARIZATION

Fractional
atomicpolarizationof the level
underconsideration

Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

Anisotropy of the radiation
field in a spherically symetricatmosphere
How to quantify the“degree of anisotropy’’at each point within the medium?

The anisotropy factor W = 2 A
2
J0
A= 0
J0

€

Anisotropic Illumination

OPTICAL PUMPINGATOMIC POLARIZATION

NEVER FORGET !
• POLARIZATION in a spectral line can be producedby the mere presence of population imbalances among
the sublevels pertaining to the upper and/or lower atomic
level of the line transition under consideration.
• Upper-level polarization

selective EMISSION of polarization• Lower-level polarization

selective ABSORPTION of polarization

Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

The Hanle effect• It is especially sensitive to magnetic fields for which
the Zeeman splitting is comparable to the natural widthof the upper (or lower) level of the spectral line used,regardless of how large the line width due to Doppler
broadening is.
• It is therefore sensitive to weaker magnetic fields than the
Zeeman effect: from at least 1 milligauss to a few hundreds ofgauss.
• It is also sensitive to magnetic fields that are tangled on scales
too small to be resolved [e.g., the Hanle-effect investigation by Trujillo Bueno et al.

(2004; Nature, 430, 326) showed that the bulk of the “quiet” photosphere is seething with tangled

magnetic fields at subresolution scales, with <B>~130 gauss, which may be important for theoverall energy balance of the solar atmosphere].
Javier Trujillo Bueno (IAC; Tenerife; Spain)

Talk at Solar-C science definition meeting (Tokyo, 2008)90º scattering

The Hanle effect REDUCES theline scattering polarization
amplitude (i.e., Stokes Q decreases withrespect to the B=0 G case) !
The Hanle effect ROTATES the
direction of linear polarization (i.e.,
Stokes U is NON-ZERO) !

Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

For example, the critical field is
B = 23 G for the Sr I 4607 line.

Moreover: in forward scattering, whenobserving at the solar disk center, theHanle effect CREATES linear
polarization in many spectral lines

Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

Selective emission versus Selective absorption
and the Hanle effect in forward scattering(Trujillo Bueno et al. 2002; Nature 415, 403)

Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

The He I 10830 A multiplet

1

Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

Solar prominence case: 90º scattering

In the off-limb case (90º scatteringgeometry) the main process that
contributes to the emergent Q/I
is SELECTIVE EMISSION, andThe solar prominence case: spectropolarimetricobservation versus quantum theory.
Clear
observationalsignature of the
Hanle effect:

Red line: 1-1+2-1

Blue line: 0

1

Linear polarization:
Scattering+HanleNO

rotation of thedirectionof polarization of
the scattered
light.

Linear polarization:
Scattering+Hanle

B=26 G
Inclination=25º
Azimuth=160º
Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

NO

Circular polarization:
Longitudinal Zeeman effectSolar filament case: forward scattering

In the on-disk case (forward
scattering geometry)
TWO processes contribute to
the emergent Q/I , namely
SELECTIVE EMISSION and
SELECTIVE ABSORPTION, andThe coronal filament case: forward scatteringand the Hanle effect at the solar disk center
QuantumtheoryYES!

Classical
theory

B=20 G
Inclination=105º

Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

In forward scattering the Hanle effect creates linear polarization in many spectral lines

Ca I 4227 chromospheric line

ATOMPOLsignalObservation taken by
Joos using ZIMPOL
at IRSOL (Locarno)
ATOMPOLsignalLinear polarization
created by
the Hanle effectof an inclined fieldin forward scattering

Note:
NO Zeeman effect !

Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

THE K-line of Ca IIOBSERVATION AT THE SOLAR DISK CENTER“QUIET” CHROMOSPHERE !

(taken by Stenflo et al. 2006 using ZIMPOL at Kitt Peak)

ATOMPOLsignals

Forward scattering signals
Linear Polarization(due to atomic level polarization)

ATOMPOLsignals

No Zeeman effect !

Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

Circular Polarization

On-disk spectropolarimetric observation ofpolar faculae in the He I 10830 triplet using TIP( Observation with TIP taken in collaboration with M. Collados )Silicon Photospheric Line
Chromospheric He I Triplet

ATOMPOL signal

ATOMPOL signal

ATOMPOL signal
Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

Zeeman signal

Magnetic Mappers of the Solar Atmosphere•

How to infer the thermal and magnetic structure of the solar
chromosphere and its coupling with the underlying photosphere ?

•How to determine the magnetic fields that confine the plasma ofstructures embedded in the solar chromosphere and corona ?

• How to explore the magnetic fied topology of coronal loops andarcades ?

Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

(1) How to explore the magnetism of
the solar chromosphere ?

Solar Chromosphere

Q>0This is a NEGATIVE of aspectroheliogram at the line
center of the Ca II K-line
taken by J. Harvey many
years ago at Kitt Peak.
One has the strong impressionof HEIGHT in these cloud andfibril features !
Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting

Here, between the thin solar photosphere and themillion-degree corona dominance of the physics passes
from hydrodynamic to magnetic forces ...

Another reason to investigate the magnetismof the “quiet” solar chromosphere
The ubiquitous presence of small-scale magnetic fields inthe “quiet” solar photosphere might have several importantconsequences for the overlying solar atmosphere, such asubiquity of reconnecting current sheets and heatingprocesses.
Therefore, it is now even more important to carry out
detailed investigations on the thermal and magnetic
structure of the solar chromosphere.

Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

Which spectral lines should
we use for “mapping” themagnetic field of thesolar chromosphere ?

Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

Suggestion 1:
The Hanle and Zeeman effects
in the IR triplet of Ca II

Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

In sunspots the polarization of the Ca II IR triplet is dominated by the Zeeman effectSuitable tool for determining the 3D structure of sunspot magnetic fields (see, e.g., Socas Navarro 2005)
Intensity image

Photospheric line close to the IR triplet of Ca II

Chromospheric 8498 line of the Ca II IR triplet

Chromospheric 8542 line of the Ca II IR triplet

Circular polarization images

In sunspots the polarization of the Ca II IR triplet is dominated by the Zeeman effect

The determination of the 3D structure ofsunspot magnetic fields can be done by interpretingthe observed Stokes profiles of the Ca II
IR triplet through the application of the non-LTE
inversion code of Stokes profiles induced by the
Zeeman effect of Socas-Navarro, Trujillo bueno
and Ruiz Cobo (2000; ApJ).

The model resulting from the application of our non-LTE
inversion code of Stokes profiles induced by the Zeeman
effect reveals a complex topology with areas of
opposite-sign torsion, suggesting that flux-ropes of
opposite helicities may coexist together in the same spot.
(see Socas-Navarro 2005).

Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

The Hanle and Zeeman effects in the Ca II IR triplet as athermometer and magnetometer of the (“quiet”) solar chromosphere( a fibrilar dominated-magnetism medium ! )( Manso Sainz & Trujillo Bueno 2007; 2009; Trujillo Bueno et al. 2009)

Intensity image of A QUIET REGION at the line center of the 8542 line of ionized calcium

SLIT( From Cauzzi et al. 2008 )The Hanle and Zeeman
effects in action in the
QUIET solar chromosphere.

Observations with ZIMPOL @ THEMIS
Stokes Iof the polarization in the Ca II IR-triplet(Trujillo Bueno, Ramelli, Manso Sainz & Bianda 2009)

8542 line of Ca II
Q/ISpectrograph’s
SLIT

U/I

Stokes Q changes its amplitude,
but it remains positive

Stokes U changes its sign !

Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

V/I
Circularpolarization createdby the LONGITUDINALZEEMAN effectIn the “quiet” chromosphere thepolarization of the Ca II IR triplet is such that:• Stokes V (the circular polarization) is
dominated by Mr. Zeeman.

• Stokes Q and U (the linear
polarization) are dominated by atomic
level polarization and by Mr. Hanle.
Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

The generation and transfer of polarized radiation
Equations ?

see the monograph by Landi Degl’Innocenti & Landolfi (2004)

Numerical method of solution ?

Trujillo Bueno (1999; 2003)

Multilevel Hanle-effect RT computer program ?

Manso Sainz & Trujillo Bueno (2003)

Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

The atomic polarization of this upper
level is very sensitive to magnetic fieldsof the order of a few gauss.

Critical Hanle field(in gauss)

Their atomic polarization (population imbalancesand quantum coherences) are sensitive tomagnetic fields between 0.001 and 0.1 G.
Level’s lifetime(in seconds)

Level’s Landé factor

Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

1D models of the solar atmosphere

FAL-C (HOT)M-CO (COOL)

Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

Spectropolarimetric observations close to the polar regions(see Tsuneta et al. 2008)

Spectrograph’s SLITFirst observation of scattering polarization in
the IR triplet of Ca II in the “quiet” Sun

Weakest Line: 8498

Strongest Line: 8542?

?

The Ca II 8662 and 8542 lines were expected to show negligible linear polarization. However, theQ/I observations of Stenflo et al. (2000) showed well defined polarization peaks (see the figure).
“This observational result further underscores that we are dealing with a fundamental
problem, for which we lack a physical explanation” (Stenflo et al. 2000).

The calculated Q/I linear polarization of
the Ca II IR-triplet in a (HOT) semi-empiricalmodel of the solar atmosphere(From Manso Sainz & Trujillo Bueno 2003; Phys. Rev. Letters 91, 111102)

WITHOUT lower-level polarization
Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

WITH lower-level polarization

Scattering Polarization in the Ca II IR triplet
Results for the FAL-C (HOT) and M-CO (COOL) models for B=0 G(From Manso Sainz & Trujillo Bueno 2001; 2007)

HOT model

M-CO

COOL model

0G

The Hanle effect in the Ca II IR triplet
Results for the FAL-C (HOT) model for a horizontal field with B=5 mGpointing to you (red), perpendicular to you (green) and away from you (blue)(From Manso Sainz & Trujillo Bueno 2007)

The Hanle and Zeeman
effects in action in the
QUIET solar chromosphere.

Observations with ZIMPOL @ THEMIS
Stokes Iof the polarization in the Ca II IR-triplet(Trujillo Bueno, Ramelli, Manso Sainz & Bianda 2009)

8542 line of Ca II
Spectrograph’s

Q/I

SLIT

Hanle DEPOLARIZATIONof thescattering polarization

U/I

Hanle ROTATION ofthe direction of
linear polarization

Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

V/I
Circularpolarization createdby the LONGITUDINALZEEMAN effectThis type of polarization signals produced by ATOMIC LEVEL POLARIZATION
and the HANLE effect in the solar atmosphere should be exploited to:(1) explore the thermal and magnetic structure of the solar chromosphere(2) evaluate the degree of realism of MHD simulations of the chromosphere

CHROMOSPHERE

PHOTOSPHERE

Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

Log(B) [G](Snapshot taken from Wedemeyer-Bohm et al. 2005)

(B) How to infer the magnetic fields that confine the plasma ofstructures embedded in the solar chromosphere and corona ?

Coronal Filament(seen against thebright solar disk)

This movie shows
intensity images of thesolar atmosphere atconsecutive wavelengths

going from thecontinuum to the line
center of the H-alphaline.

Courtesy of L. Rouppe van der Voort(SSVT @ Canary Islands observatories)

How to infer the magnetic fields that confine the plasma ofstructures embedded in the solar chromosphere and corona ?

Solar Prominences(seen against the dark
background of the sky)

Courtesy of T. Berger

How to infer the strength and topology of the magnetic field in
more active regions (e.g., emerging flux regions, active region filaments, flaring regions, etc.)

Active Regions(seen on-disk)

DOT archiveSUGGESTION 2: By observing and interpreting the polarization
signals produced by the joint action of atomic level polarization andthe Hanle and Zeeman effects in the He I 10830 triplet.
Images of A SMALL ACTIVE REGION in the IR continuum and in the He I 10830 line

Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

The He I 10830 triplet shows clear(Hanle+Zeeman) polarization signals inplasma structures of the solar
chromosphere and corona, such as:• Filaments and prominences (e.g., Lin et al. 1998; Trujillo Bueno et al. 2002; Merenda et al.2006)• Active region filaments (e.g., Kuckein et al. 2009; Merenda 2008: PhD thesis)• Regions of emerging flux (e.g., Solanki et al. 2003)• Active regions (e.g., Lagg et al. 2006)• Polar faculae (e.g., see one of previous images)• Flaring regions (e.g., Sasso et al. 2007)• Chromospheric spicules (e.g., Trujillo Bueno et al. 2005)

NOTE: it is crucial to carry out the calculations taking into account the Paschen-Back effectand the impact of level crossings and repulsions on the atomic level polarization.

Upper levels of He I 10830

Upper levels of He I 5876

Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

The polarization of the He I 10830
triplet is such that:• Stokes V (the circular polarization) is
dominated by Mr. Zeeman (longitudinal).

• Stokes Q and U (the linear polarization) is
caused by the joint action of ATOMPOL,
Mr. Hanle and Mr. Zeeman (transversal).
Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

Simulated disk-center observation of the intensity and polarizationof the He I 10830 triplet for a magnetic field vector with B=500 G,
inclined by 80 degrees with respect to the local vertical.
ATOMPOL + Paschen-Back(From Trujillo Bueno & Asensio Ramos 2007, ApJ)

Stokes I

Stokes Q

Only PB
Only Zeeman

Stokes U

Stokes V

Applications in Solar Physics
The magnetic field that channels the
dynamic jets that we call SPICULES

Hinode solar spacetelecope archiveHow to infer the magnetic field vector of solar chromospheric spicules?
slit

DOT H-alpha wing image showing
spicules emanating from network
magnetic concentrations.

Difficult to measure but“easy” to interpret

Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

We take into account radiative transfer in a slab
whose optical thickness is chosen to fit the observed
Stokes I profile.
The observed Stokes Q, U and V profiles are then used
to infer the magnetic field vector (its strength, its inclination
with respect to the solar local vertical, and its azimuth).
The He I 10830 A multiplet
1

2

1
Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

Geometry of the problem
We assume that a slab ofneutral Helium atoms isilluminated by the continuum
anisotropic radiation fieldcoming from the underlying
solar photosphere.

Z

REFERENCE
DIRECTION

e2

θB

B

χΒ
Y
X

e1

Ω

Wave
Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

Spectropolarimetric observations in the He I 10830 line
vs. RT modeling of the Hanle and Zeeman effects.
(Trujillo Bueno et al. 2005; ApJ Letters, 619, L191)

SPICULESQUIET REGIONS
Observationalsignature of the
Hanle effect:
rotation of thedirectionof polarization of
the scattered light.

B=10 G
Inclination=37º
Azimuth = 173º
V=13 km/s

τ=3

Do we have magnetic canopies in the most“quiet” regions of the solar chromosphere ?
slit

QUESTION
Can we explore via
spectro-polarimetry in the He I
10830 triplet the structure of
the magnetic field in “quiet”
regions like this one, where
there seems to be insufficientchromospheric material
to trace it ?

DOT H-alpha wing image showing
spicules emanating from network
magnetic concentrations.
Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

Cartoon Model of the “Quiet” Solar Chromosphere(From Judge 2007)

Cartoon Model of the “Quiet” Solar Chromosphere
Observer(From Judge 2007)

The amplitude of the emergent polarization must
depend on the optical thickness of the absorbing layer.
Let us see how it varies assuming:(1)

a horizontal field between 10 and 100 gauss.

(2)

disk-center observation (forward-scattering geometry).

Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

The He I 10830 linear polarization signal created by the
Hanle effect of an inclined field when observing at thesolar disk center (forward scattering geometry)
NOTE that the smaller the optical thickness of the plasma structure the smaller the Q/I amplitude !

Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

Can we detect with the Tenerife IR Polarimeter He I 10830 linear
polarization signals when observing “QUIET” inter-network regionsat the solar disk center?
If detected, such a Hanle-effect signal would be due to the presenceof an inclined magnetic field in the “QUIET” chromosphere !

Hanle signal !
Result of our HAZEL
inversion:

B=47 G
Inclination=47º
Zeeman signal !

(From Asensio Ramos & Trujillo Bueno 2009; SPW5)

The Astrophysical Journal, 683, 565, 2008

Exposure times (T) needed for detecting X/I signals with the indicatedpolarimetric sensitivity (PS), with 0.5” and a spectral resolution of
0.05 Angstroms, and assuming a 1m space telescope having
an overall throughput of 5% .

• Ca II IR-triplet lines• He I 10830 triplet• PS=0.1% T=0.32 sec• PS=0.1% T=0.16 sec• PS=0.01%

T=32 sec• PS=0.01%

T=16 sec

Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

The polarization of the IR triplet of Ca II
Not so good news

Good news•

Good choice to study both, the “quiet” andthe active Sun magnetism.

•

Provides information on the thermal andthe magnetic structure, all the way up fromthe photosphere to the bulk of thechromosphere.

•

The polarization signals are sensitive tomagnetic strengths from milligauss to kG
fields.

•

Ideal choice to evaluate the reliability of
MHD models of thephotosphere+chromosphere via spectral
synthesis and comparison with
spectropolarimetric observations.

•Not the ideal choice for studying themagnetic field that confines theplasma of structures embedded in thesolar chromosphere and corona (e.g.,
prominences, filaments, spicules, …).

•

The forward scattering signals arerather small, but neverthelessmeasurable through longer
integration times.

•

Stokes inversion of the magnetic field
vector is possible, but requires toinfer first a model for thethermal+density stratification.

Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

The polarization of the He I 10830 triplet
Not so good news

Good news•

Ideal choice for studying the magnetic
field that confines the plasma ofstructures embedded in the solar
chromosphere and corona (e.g.,
prominences, filaments, spicules).

•Not the best choice to study themagnetism of the “quiet” chromosphere.

•

Difficult to obtain information on thethermal and/or density structure.

•

It is also suitable for obtainig some
information on the magnetic field
vector in regions of emerging flux,
flaring regions, sunspots, etc.

•

Difficult to obtain information on theheight corresponding to the inferredmagnetic field vector.

•

Photospheric lines present in thesame spectral region, so informationon the photospheric-chromosphericcoupling can also be obtained.

•

Not an ideal choice to evaluate thereliability of MHD models of the solar
atmosphere.

•

Stokes inversion of the magnetic field
vector is already possible (with theHanle+Zeeman code HAZEL).

Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

How to explore the magnetic fied topology of coronal loops and arcades ?
SUGGESTION 3: Build a EUV imaging polarimeter in order to map themagnetic fieds of coronal loops and arcades

Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)

Can we expect scattering polarization signals in spectral
lines at EUV wavelengths for which the underlying quiet
solar disk is seen completely dark ?
•For many EUV lines their lower level is the upper or lower
level of a forbidden line at visible wavelengths, which arepolarized due to the anisotropic illumination in theforbidden line.

•

This lower-level polarization is transferred to the upper
level of the EUV line by collisional excitation.

•

Therefore, since the upper level of the EUV line is polarized,
we will have measurable scattering polarization signals
caused by the ensuing selective emission processes.

•

Contrary to the case of forbidden line polarimetry, suchlinear polarization signals can be observed also in forward
scattering at the solar disk centercoronal magnetic
mapper.

See the paper by Manso Sainz & TB (2009) in the proceedings of the Solar Polarization Workshop 5 (SPW5)

Theoretical prediction of the linear polarization produced by coronalloops in the EUV Fe X line at 174.5 Angstroms
From Manso Sainz & TB (2009) (see SPW5 paper)

Horizontal Magnetic Field Case
Top of the loop as seen at the disk-center

FORWARD scattering geometry
TOP of the loop as seen at disk center

BConcluding comments• If you want to do something scientifically challenging
put in SOLAR-C a spectropolarimeter for measuring
simultaneously the polarization in photospheric andchromospheric lines (e.g., for the spectral region of
the IR triplet of Ca II and/or for that of the He I
10830 triplet).
• If, in addition, you want to do something
technologically challenging put in SOLAR-C a EUV
imaging polarimeter (i.e., a TRACE-like instrument
BUT capable of obtaining also linear polarization imagesof coronal loops).

Concluding Comments• I bear no doubt that (Hanle + Zeeman)

spectropolarimetry will be arevolutionary technique in 21st
century astrophysics.

• JAXA + ESA + NASA should takeadvantage of our joint knowledge inthis field to open this NEW

diagnostic window to the Universe.
Javier Trujillo Bueno (IAC; Tenerife; Spain)
Talk at Solar-C science definition meeting (Tokyo, 2008)