Some polarization diagnostics to explore themagnetism of the upper chromosphere and TR
Javier Trujillo Bueno(IAC, Tenerife, Spain)

Q>0

Courtesy of J. Harvey

H-alpha intensity image (DOT archive)
Javier Trujillo Bueno
2nd SOLAR-C Science Definition Meeting
Tokyo, March 2010

“Quiet” chromosphere
NOTE: Stokes I is insensitive to B
0 G

1000 GThe only way to obtain
quantitative empirical informationon the magnetic field vector inthe solar atmosphere is via themeasurement and physicalinterpretation of the emergent
spectral line polarization.
Stokes parameters
Javier Trujillo Bueno
2nd SOLAR-C Science Definition Meeting
Tokyo, March 2010

Physical mechanisms that control thepolarization of the spectral lines thatoriginate in the solar atmosphere

The Zeeman effect

Scattering processes and the Hanle effectJavier Trujillo Bueno
2nd SOLAR-C Science Definition Meeting
Tokyo, March 2010

The message of this talk
The Hanle effect is a key
physical mechanism that should
be increasingly exploited forfacilitating the exploration ofmagnetic fields in the outersolar atmosphere (upperchromosphere, transition regionand corona).

Javier Trujillo Bueno
2nd SOLAR-C Science Definition Meeting
Tokyo, March 2010

The impact of the Hanle effect on thelinear polarization produced byscattering processes

90º scattering geometry
The Hanle effect REDUCES theamplitude of the line scatteringpolarization signal(i.e.,Stokes Q decreases with respect tothe B=0 G case) !

The Hanle effect ROTATES thedirection of linear polarization(i.e., Stokes U is NON-ZERO) !

Magnetic splitting of the Level = Natural width of the Level

Javier Trujillo Bueno
2nd SOLAR-C Science Definition Meeting
Tokyo, March 2010

The Hanle and Zeeman
effects in action in theQUIET solar chromosphere.

Observations with ZIMPOL @ THEMIS
Stokes Iof the polarization in the Ca II IR-triplet(TB, Ramelli, Manso Sainz & Bianda 2010)

8542 line of Ca II

Spectrograph’s

Q/I

SLIT

U/I

Hanle DEPOLARIZATIONof thescattering polarization

Hanle ROTATION ofthe direction oflinear polarization

V/I

Javier Trujillo Bueno
2nd SOLAR-C Science Definition Meeting
Tokyo, March 2010

Circularpolarization createdby the LONGITUDINALZEEMAN effectNew discovery space 1
2D spectropolarimetry of the Ca II
IR triplet with SOLAR-C option-Bwould allow us to map the spatial andtemporal variations of thechromospheric magnetic field with
unprecented polarimetric sensitivity athigh spatial and temporal resolution.
Javier Trujillo Bueno
2nd SOLAR-C Science Definition Meeting
Tokyo, March 2010

Two problems (and type of radiative transfer codes) for
the interpreta:on and modelling of
the polariza:on observed in spectral lines• The diagnostic problem of plasma
structures embedded in optically thinregions of the outer solar chromosphere• The diagnostic problem of thechromospheric and TR plasma itself.
Javier Trujillo Bueno
2nd SOLAR-C Science Definition Meeting
Tokyo, March 2010

The diagnostic problem of plasma structures embedded
in optically thin regions of the solar chromosphere.

It requires solving a “simplified”
non-LTE problem of the 2nd kind

Javier Trujillo Bueno
2nd SOLAR-C Science Definition Meeting
Tokyo, March 2010

The “simplified” non‐LTE Problem of the Second Kind

Coefficientsof the radiativetransfer equation

I, Q, U, V

GIVEN
Incident Radiation

Javier Trujillo Bueno
2nd SOLAR-C Science Definition Meeting
Tokyo, March 2010

With the computer program HAZEL (HAnle and ZEeman Light;see Asensio Ramos, Trujillo Bueno & Landi Degl’Innocenti 2008; ApJ) we assume a slab
whose optical thickness is chosen to fit theobserved 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
121
Javier Trujillo Bueno
2nd SOLAR-C Science Definition Meeting
Tokyo, March 2010

He I 10830 spectropolarimetric observations of off-limb spicules( From Centeno, Trujillo Bueno & Asensio Ramos 2009; ApJ)NOTE: the longitudinal Zeeman
effect is of great help here !

HAZEL inversion of He I 10830 observations of spicules in quiet regions(From Centeno, Trujillo Bueno & Asensio Ramos 2009; ApJ)

B = 48 G
Inclination = 35º

Inversion example

Azimuth = 0.15º

Javier Trujillo Bueno
2nd SOLAR-C Science Definition Meeting
Tokyo, March 2010

HAZEL inversion of He I 10830 observations of spicules in quiet regions(From Centeno, Trujillo Bueno & Asensio Ramos 2009; ApJ)

Javier Trujillo Bueno2nd SOLAR-C Science Definition Meeting
Tokyo, March 2010

At least 50 gauss at aheight of about 2000 km
in chromospheric spicules.

New discovery space 2• With SOLAR-C option-B we would be
able to determine with unprecedented
spatial and temporal resolution thestrength and geometry of themagnetic field in a variery ofchromospheric and coronal plasma
structures (e.g., spicules, prominences
and active region filaments).
Javier Trujillo Bueno
2nd SOLAR-C Science Definition Meeting
Tokyo, March 2010

The diagnostic problem of thechromospheric and TR plasma itself.

Anisotropy of the radiation field
WITHIN a stellar atmosphere
2J0
A= 0J0
Javier Trujillo Bueno
2nd SOLAR-C Science Definition Meeting
Tokyo, March 2010

The general non‐LTE Problem of the Second Kind
Equations ?

Chapter 7 of Landi Degl’Innocenti & Landolfi (2004)

Numerical methods of solution ?

TB (1999; 2003)

Multilevel RT computer programs ?

Manso Sainz & TB (2003)
Stepan (2008; PhD thesis)

Javier Trujillo Bueno
2nd SOLAR-C Science Definition Meeting
Tokyo, March 2010

Some interes:ng spectral line choices :• The IR triplet of Ca II•(see Manso Sainz & Trujillo Bueno 2003; Phys. Rev. Letters)• The H-alpha line
• The Mg II k-line
Javier Trujillo Bueno
2nd SOLAR-C Science Definition Meeting
Tokyo, March 2010

Scattering polarization andthe Hanle effect in the H-alpha line
(Stepan & Trujillo Bueno 2010, ApJ)

Javier Trujillo Bueno
2nd SOLAR-C Science Definition Meeting
Tokyo, March 2010

Response of the emergent Q profile of H-alpha to the Hanle effect of an inclined field(Stepan & TB 2010)

Upper
chromosphere

Q/I response function

Response of the Q/I profile

Javier Trujillo Bueno
2nd SOLAR-C Science Definition Meeting
Tokyo, March 2010

Observed Q/I in the H-alpha line
Observed Q/I profile(see Gandorfer’s atlas ofthe Second Solar Spectrum)

Javier Trujillo Bueno
2nd SOLAR-C Science Definition Meeting
Tokyo, March 2010

The Hanle effect in the H-alpha line is very sensitive to thepresence of gradients of the magnetic field strength in the upperchromosphere (see Stepan & TB 2010; ApJ)
Height-variation of the magnetic field strength needed to produce the observed Q/I ?

An abrupt magnetization in theupper chromosphere of the “quiet” Sun ?

Javier Trujillo Bueno
2nd SOLAR-C Science Definition Meeting
Tokyo, March 2010

The Hanle effect in the H-alpha line
(Stepan & TB 2010; ApJ)

Javier Trujillo Bueno
2nd SOLAR-C Science Definition Meeting
Tokyo, March 2010

On the probable existence of an abrupt magnetization in
the upper chromosphere of the “quiet” Sun(Stepan & TB 2010; ApJ)

Height-variation of the magnetic field strength needed to produce the observed Q/I

Javier Trujillo Bueno
2nd SOLAR-C Science Definition Meeting
Tokyo, March 2010

On the probable existence of an abrupt magnetization in
the upper chromosphere of the “quiet” Sun(Stepan & TB 2010; ApJ)

The resulting theoretical Q/I profile of the H-alpha line

Javier Trujillo Bueno
2nd SOLAR-C Science Definition Meeting
Tokyo, March 2010

New discovery space 3
H-alpha spectropolarimetry with
SOLAR-C option-B would allow us toexplore with high angular and temporal
resolution the spatial structure of themagnetic field in the upper
chromosphere of the Sun.

Javier Trujillo Bueno
2nd SOLAR-C Science Definition Meeting
Tokyo, March 2010

Ly-alpha intensity imageof the TR (see Vourlidas et al. 2010)

How to explore the magnetismof the transition region ?
Quiet Transition Region(detail of a supergranular cell)

Javier Trujillo Bueno
2nd SOLAR-C Science Definition Meeting
Tokyo, March 2010

Radiative transfer modeling of the intensity andscattering polarization of the Mg II k-line and of its
sensitivity to the Hanle effect in the solar TR(Results from an ongoing work in collaboration with M. Sampoorna & J. Stepan)• Radiative transfer code with Partial Frequency
Redistribution (PRD) and polarization (see Sampoorna &Trujillo Bueno 2010; ApJ).

• Model atmospheres used: for the moment semiempirical models like FAL-C, but we can do the RT
calculations with PRD + scattering polarization inMHD models also.

Javier Trujillo Bueno
2nd SOLAR-C Science Definition Meeting
Tokyo, March 2010

The Hanle effect at the Mg II k-line center

Horizontal magnetic fieldwith a random azimuth(Results from an ongoing collaboration
with M. Sampoorna & J. Stepan)

Saturation field ~ 100 G

Javier Trujillo Bueno
2nd SOLAR-C Science Definition Meeting
Tokyo, March 2010

New discovery space 4• With SOLAR-C option-B we could
discover and explore for the firsttime scattering polarization in aTransition Region line, opening thus anovel diagnostic window on thephysical conditions of the outer solaratmosphere.

Javier Trujillo Bueno
2nd SOLAR-C Science Definition Meeting
Tokyo, March 2010

Concluding comment
With SOLAR-C option-B

JAXA + NASA + ESA
would make feasible a new revolution
in our empirical understanding ofsolar magnetism.
Javier Trujillo Bueno
2nd SOLAR-C Science Definition Meeting
Tokyo, March 2010