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Author name code: trujillo-bueno
ADS astronomy entries on 2022-09-14
author:"Trujillo Bueno, Javier"
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Title: The transfer of polarized radiation in resonance lines with
partial frequency redistribution, J-state interference, and arbitrary
magnetic fields. A radiative transfer code and useful approximations
Authors: Alsina Ballester, E.; Belluzzi, L.; Trujillo Bueno, J.
2022A&A...664A..76A Altcode: 2022arXiv220412523A
<BR /> Aims: We present the theoretical framework and numerical
methods we have implemented to solve the problem of the generation and
transfer of polarized radiation in spectral lines without assuming
local thermodynamical equilibrium, while accounting for scattering
polarization, partial frequency redistribution (due to both the
Doppler effect and elastic collisions), J-state interference, and
hyperfine structure. The resulting radiative transfer code allows
one to model the impact of magnetic fields of an arbitrary strength
and orientation through the Hanle, incomplete Paschen-Back, and
magneto-optical effects. We also evaluate the suitability of a series
of approximations for modeling the scattering polarization in the
wings of strong resonance lines at a much lower computational cost,
which is particularly valuable for the numerically intensive case of
three-dimensional radiative transfer. <BR /> Methods: We examine the
suitability of the considered approximations by using our radiative
transfer code to model the Stokes profiles of the Mg II h & k lines
and of the H I Lyman-α line in magnetized one-dimensional models of
the solar atmosphere. <BR /> Results: Neglecting Doppler redistribution
in the scattering processes that are unperturbed by elastic collisions
(i.e., treating them as coherent in the observer's frame) produces a
negligible error in the scattering polarization wings of the Mg II
resonance lines and a minor one in the Lyman-α wings, although it
is unsuitable to model the cores of these lines. For both lines, the
scattering processes that are perturbed by elastic collisions only
give a significant contribution to the intensity component of the
emissivity. Neglecting collisional as well as Doppler redistribution
(so that all scattering processes are coherent) represents a rough
but suitable approximation for the wings of the Mg II resonance lines,
but a very poor one for the Lyman-α wings. The magnetic sensitivity
in the scattering polarization wings of the considered lines can be
modeled by accounting for the magnetic field in only the η<SUB>I</SUB>
and ρ<SUB>V</SUB> coefficients of the Stokes-vector transfer equation
(i.e., using the zero-field expression for the emissivity).
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Title: TIC: A Stokes Inversion Code for Scattering Polarization with
Partial Frequency Redistribution and Arbitrary Magnetic Fields
Authors: Li, H.; del Pino Alemán, T.; Trujillo Bueno, J.; Casini, R.
2022ApJ...933..145L Altcode: 2022arXiv220515666L
We present the Tenerife Inversion Code (TIC), which has been developed
to infer the magnetic and plasma properties of the solar chromosphere
and transition region via full Stokes inversion of polarized spectral
lines. The code is based on the HanleRT forward engine, which takes into
account many of the physical mechanisms that are critical for a proper
modeling of the Stokes profiles of spectral lines originating in the
tenuous and highly dynamic plasmas of the chromosphere and transition
region: the scattering polarization produced by quantum level imbalance
and interference (atomic polarization), the effects of frequency
coherence in polarized resonance scattering (partial redistribution),
and the impact of arbitrary magnetic fields on the atomic polarization
and the radiation field. We present first results of atmospheric and
magnetic inversions, and discuss future developments for the project.
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Title: CASPER: A mission to study the time-dependent evolution of
the magnetic solar chromosphere and transition regions
Authors: Orozco Suárez, D.; del Toro Iniesta, J. C.; Bailén, F. J.;
López Jiménez, A.; Balaguez Jiménez, M.; Bellot Rubio, L. R.;
Ishikawa, R.; Katsukawa, Y.; Kano, R.; Shimizu, T.; Trujillo Bueno,
J.; Asensio Ramos, A.; del Pino Alemán, T.
2022ExA...tmp...26O Altcode:
Our knowledge about the solar chromosphere and transition region (TR)
has increased in the last decade thanks to the huge scientific return
of space-borne observatories like SDO, IRIS, and Hinode, and suborbital
rocket experiments like CLASP1, CLASP2, and Hi-C. However, the magnetic
nature of those solar regions remain barely explored. The chromosphere
and TR of the Sun harbor weak fields and are in a low ionization stage
both having critical effects on their thermodynamic behavior. Relatively
cold gas structures, such as spicules and prominences, are located in
these two regions and display a dynamic evolution in high-resolution
observations that static and instantaneous 3D-magnetohydrodynamic (MHD)
models are not able to reproduce. The role of the chromosphere and TR
as the necessary path to a (largely unexplained) very hot corona calls
for the generation of observationally based, time-dependent models
of these two layers that include essential, up to now disregarded,
ingredients in the modeling such as the vector magnetic field. We
believe that the community is convinced that the origin of both the
heat and kinetic energy observed in the upper layers of the solar
atmosphere is of magnetic origin, but reliable magnetic field
measurements are missing. The access to sensitive polarimetric
measurements in the ultraviolet wavelengths has been elusive until
recently due to limitations in the available technology. We propose a
low-risk and high-Technology Readiness Level (TRL) mission to explore
the magnetism and dynamics of the solar chromosphere and TR. The mission
baseline is a low-Earth, Sun-synchronous orbit at an altitude between
600 and 800 km. The proposed scientific payload consists of a 30 cm
aperture telescope with a spectropolarimeter covering the hydrogen
Ly-alpha and the Mg II h&k ultraviolet lines. The instrument shall
record high-cadence, full spectropolarimetric observations of the
solar upper atmosphere. Besides the answers to a fundamental solar
problem the mission has a broader scientific return. For example,
the time-dependent modeling of the chromospheres of stars harboring
exoplanets is fundamental for estimating the planetary radiation
environment. The mission is based on technologies that are mature
enough for space and will provide scientific measurements that are
not available by other means.
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Title: Spectropolarimetric observations of the solar atmosphere in
the Hα 6563 Å line
Authors: Jaume Bestard, J.; Trujillo Bueno, J.; Bianda, M.; Štěpán,
J.; Ramelli, R.
2022A&A...659A.179J Altcode: 2022arXiv220103815J
We present novel spectropolarimetric observations of the hydrogen
Hα line taken with the Zürich Imaging Polarimeter (ZIMPOL) at
the Gregory Coudé Telescope of the Istituto Ricerche Solari Locarno
(IRSOL). The linear polarization is clearly dominated by the scattering
of anisotropic radiation and the Hanle effect, while the circular
polarization is dominated by the Zeeman effect. The observed linear
polarization signals show a rich spatial variability, the interpretation
of which would open a new window for probing the solar chromosphere. We
study their spatial variation within coronal holes, finding a different
behaviour for the U/I signals near the north and south solar poles. We
identify some spatial patterns, which may facilitate the interpretation
of the observations. In close-to-the-limb regions with sizable circular
polarization signals, we find similar asymmetric Q/I profiles. We
also show examples of net circular polarization profiles (NCP), along
with the corresponding linear polarization signals. The application
of the weak field approximation to the observed circular polarization
signals gives 10 G (40-60 G) close to the limb quiet (plage) regions
for the average longitudinal field strength over the spatio-temporal
resolution element.
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Title: Novel framework for the three-dimensional NLTE inverse problem
Authors: Štěpán, Jiří; del Pino Alemán, Tanausú; Trujillo
Bueno, Javier
2022A&A...659A.137S Altcode: 2022arXiv220101504S
The inversion of spectropolarimetric observations of the solar upper
atmosphere is one of the most challenging goals in solar physics. If
we account for all relevant ingredients of the spectral line formation
process, such as the three-dimensional (3D) radiative transfer out
of local thermodynamic equilibrium (NLTE), the task becomes extremely
computationally expensive. Instead of generalizing 1D methods to 3D, we
have developed a new approach to the inverse problem. In our meshfree
method, we do not consider the requirement of 3D NLTE consistency
as an obstacle, but as a natural regularization with respect to the
traditional pixel-by-pixel methods. This leads to more robust and
less ambiguous solutions. We solve the 3D NLTE inverse problem as
an unconstrained global minimization problem that avoids repetitive
evaluations of the Λ operator. Apart from the 3D NLTE consistency,
the method allows us to easily include additional conditions of
physical consistency such as the zero divergence of the magnetic
field. Stochastic ingredients make the method less prone to ending up
within the local minima of the loss function. Our method is capable
of solving the inverse problem faster by several orders of magnitude
than by using grid-based methods. The method can provide accurate and
physically consistent results if sufficient computing time is available,
along with approximate solutions in the case of very complex plasma
structures or limited computing time.
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Title: The polarization angle in the wings of Ca I 4227: A new
observable for diagnosing unresolved photospheric magnetic fields
Authors: Capozzi, Emilia; Alsina Ballester, Ernest; Belluzzi, Luca;
Trujillo Bueno, Javier
2022A&A...657A..44C Altcode: 2021arXiv211108967C
Context. When observed in quiet regions close to the solar limb, many
strong resonance lines show conspicuous linear polarization signals,
produced by scattering processes (i.e., scattering polarization), with
extended wing lobes. Recent studies indicate that, contrary to what
was previously believed, the wing lobes are sensitive to the presence
of relatively weak longitudinal magnetic fields through magneto-optical
(MO) effects. <BR /> Aims: We theoretically investigate the sensitivity
of the scattering polarization wings of the Ca I 4227 Å line to the
MO effects, and we explore its diagnostic potential for inferring
information on the longitudinal component of the photospheric magnetic
field. <BR /> Methods: We calculate the intensity and polarization
profiles of the Ca I 4227 Å line by numerically solving the problem
of the generation and transfer of polarized radiation under non-local
thermodynamic equilibrium conditions in one-dimensional semi-empirical
models of the solar atmosphere, taking into account the joint action
of the Hanle, Zeeman, and MO effects. We consider volume-filling
magnetic fields as well as magnetic fields occupying a fraction of
the resolution element. <BR /> Results: In contrast to the circular
polarization signals produced by the Zeeman effect, we find that the
linear polarization angle in the scattering polarization wings of Ca
I 4227 presents a clear sensitivity, through MO effects, not only to
the flux of the photospheric magnetic field, but also to the fraction
of the resolution element that the magnetic field occupies. <BR />
Conclusions: We identify the linear polarization angle in the wings
of strong resonance lines as a valuable observable for diagnosing
unresolved magnetic fields. Used in combination with observables that
encode information on the magnetic flux and other properties of the
observed atmospheric region (e.g., temperature and density), it can
provide constraints on the filling factor of the magnetic field.
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Title: Empirical relations between the intensities of Lyman lines
of H and He<SUP>+</SUP>
Authors: Gordino, M.; Auchère, F.; Vial, J. -C.; Bocchialini, K.;
Hassler, D. M.; Bando, T.; Ishikawa, R.; Kano, R.; Kobayashi, K.;
Narukage, N.; Trujillo Bueno, J.; Winebarger, A.
2022A&A...657A..86G Altcode: 2022arXiv220101519G
Context. Empirical relations between major UV and extreme UV spectral
lines are one of the inputs for models of chromospheric and coronal
spectral radiances and irradiances. They are also needed for the
interpretation of some of the observations of the Solar Orbiter
mission. <BR /> Aims: We aim to determine an empirical relation between
the intensities of the H I 121.6 nm and He II 30.4 nm Ly-α lines. <BR
/> Methods: Images at 121.6 nm from the Chromospheric Lyman-Alpha
Spectro Polarimeter (CLASP) and Multiple XUV Imager (MXUVI) sounding
rockets were co-registered with simultaneous images at 30.4 nm from the
EIT and AIA orbital telescopes in order to derive a spatially resolved
relationship between the intensities. <BR /> Results: We have obtained
a relationship between the H I 121.6 nm and He II 30.4 nm intensities
that is valid for a wide range of solar features, intensities, and
activity levels. Additional SUMER data have allowed the derivation of
another relation between the H I 102.5 nm (Ly-β) and He II 30.4 nm
lines for quiet-Sun regions. We combined these two relationships to
obtain a Ly-α/Ly-β intensity ratio that is comparable to the few
previously published results. <BR /> Conclusions: The relationship
between the H I 121.6 nm and He II 30.4 nm lines is consistent with the
one previously obtained using irradiance data. We have also observed
that this relation is stable in time but that its accuracy depends on
the spatial resolution of the observations. The derived Ly-α/Ly-β
intensity ratio is also compatible with previous results.
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Title: Demonstration of Chromospheric Magnetic Mapping with CLASP2.1
Authors: McKenzie, David; Ishikawa, Ryohko; Trujillo Bueno, Javier;
Auchere, F.; Kobayashi, Ken; Winebarger, Amy; Kano, Ryouhei; Song,
Donguk; Okamoto, Joten; Rachmeler, Laurel; De Pontieu, Bart; Vigil,
Genevieve; Belluzzi, Luca; Alsina Ballester, Ernest; del Pino Aleman,
Tanausu; Bethge, Christian; Sakao, Taro; Stepan, Jiri
2021AGUFMSH52A..06M Altcode:
Probing the magnetic nature of the Suns atmosphere requires measurement
of the Stokes I, Q, U and V profiles of relevant spectral lines (of
which Q, U and V encode the magnetic field information). Many of the
magnetically sensitive lines formed in the chromosphere and transition
region are in the ultraviolet spectrum, necessitating observations
above the absorbing terrestrial atmosphere. The Chromospheric
Layer Spectro-Polarimeter (CLASP2) sounding rocket was flown
successfully in April 2019, as a follow-on to the successful flight in
September 2015 of the Chromospheric Lyman-Alpha Spectro-Polarimeter
(CLASP). Both projects were funded by NASAs Heliophysics Technology
and Instrument Development for Science (H-TIDeS) program to develop
and test a technique for observing the Sun in ultraviolet light,
and for quantifying the polarization of that light. By demonstrating
successful measurement and interpretation of the polarization in
hydrogen Lyman-alpha and the Mg II h and k spectral lines, the CLASP
and CLASP2 missions are vital first steps towards routine quantitative
characterization of the local thermal and magnetic conditions in the
solar chromosphere. In October of 2021, we re-flew the CLASP2 payload
with a modified observing program to further demonstrate the maturity
of the UV spectropolarimetry techniques, and readiness for development
into a satellite observatory. During the reflight, called CLASP2.1,
the spectrograph slit was scanned across an active region plage to
acquire a two-dimensional map of Stokes V/I, to demonstrate the ability
of UV spectropolarimetry to yield chromospheric magnetic fields over
a large area. This presentation will display preliminary results from
the flight of CLASP2.1.
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Title: Polarization of the Lyα Lines of H I and He II as a Tool
for Exploring the Solar Corona
Authors: Hebbur Dayananda, Supriya; Trujillo Bueno, Javier; de Vicente,
Ángel; del Pino Alemán, Tanausú
2021ApJ...920..140H Altcode: 2021arXiv210701015H; 2021ApJ...920..140S
The near-Earth space weather is driven by the quick release of
magnetic free energy in the solar corona. Probing this extremely
hot and rarified region of the extended solar atmosphere requires
modeling the polarization of forbidden and permitted coronal lines. To
this end, it is important to develop efficient codes to calculate
the Stokes profiles that emerge from given three-dimensional (3D)
coronal models and this should be done taking into account the symmetry
breaking produced by the presence of magnetic fields and non-radial
solar wind velocities. We have developed such a tool with the aim
of theoretically predicting and interpreting spectropolarimetric
observations of the solar corona in permitted and forbidden lines. In
this paper, we show the results of a theoretical investigation of the
linear polarization signals produced by scattering processes in the H
I Lyα line at 1216 Å and in the He II Lyα line at 304 Å using 3D
coronal models by Predictive Science Inc. These spectral lines have very
different critical magnetic fields for the onset of the Hanle effect
(53 G and 850 G, respectively), as well as different sensitivities
to the Doppler effect caused by the solar wind velocities. We study
under which circumstances simultaneous observations of the scattering
polarization in these Lyα lines can facilitate the determination of
magnetic fields and macroscopic velocities in the solar corona.
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Title: Solving the Paradox of the Solar Sodium D<SUB>1</SUB> Line
Polarization
Authors: Alsina Ballester, Ernest; Belluzzi, Luca; Trujillo Bueno,
Javier
2021PhRvL.127h1101A Altcode: 2021arXiv210808334A
Twenty-five years ago, enigmatic linear polarization signals were
discovered in the core of the sodium D<SUB>1</SUB> line. The only
explanation that could be found implied that the solar chromosphere is
practically unmagnetized, in contradiction with other evidences. This
opened a paradox that has challenged physicists for many years. Here
we present its solution, demonstrating that these polarization signals
can be properly explained in the presence of magnetic fields in the
gauss range. This result opens a novel diagnostic window for exploring
the elusive magnetism of the solar chromosphere.
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Title: PORTA: POlarized Radiative TrAnsfer
Authors: StÄpán, JiÅí.; Trujillo Bueno, Javier
2021ascl.soft06037S Altcode:
PORTA solves three-dimensional non-equilibrium radiative transfer
problems with massively parallel computers. The code can be used for
modeling the spectral line polarization produced by the scattering
of anisotropic radiation and the Hanle and Zeeman effects assuming
complete frequency redistribution, either using two-level or multilevel
atomic models. The numerical method of solution used to find the
self-consistent values of the atomic density matrix at each point of
the model's Cartesian grid is based on Jacobi iterative scheme and on
a short-characteristics formal solver of the Stokes-vector transfer
equation that uses monotonic Bézier interpolation. The code can also
be used to compute the linear polarization of the continuum radiation
caused by Rayleigh and Thomson scattering in 3D models of stellar
atmospheres, and to solve the simpler 3D radiative transfer problem
of unpolarized radiation in multilevel systems. PORTA accepts/produces
HDF5 input/output and offers an advanced graphical user interface.
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Title: Mapping of Solar Magnetic Fields from the Photosphere to the
Top of the Chromosphere with CLASP2
Authors: McKenzie, D.; Ishikawa, R.; Trujillo Bueno, J.; Auchere, F.;
del Pino Aleman, T.; Okamoto, T.; Kano, R.; Song, D.; Yoshida, M.;
Rachmeler, L.; Kobayashi, K.; Narukage, N.; Kubo, M.; Ishikawa, S.;
Hara, H.; Suematsu, Y.; Sakao, T.; Bethge, C.; De Pontieu, B.; Vigil,
G.; Winebarger, A.; Alsina Ballester, E.; Belluzzi, L.; Stepan, J.;
Asensio Ramos, A.; Carlsson, M.; Leenaarts, J.
2021AAS...23810603M Altcode:
Coronal heating, chromospheric heating, and the heating &
acceleration of the solar wind, are well-known problems in solar
physics. Additionally, knowledge of the magnetic energy that
powers solar flares and coronal mass ejections, important drivers
of space weather, is handicapped by imperfect determination of the
magnetic field in the sun's atmosphere. Extrapolation of photospheric
magnetic measurements into the corona is fraught with difficulties and
uncertainties, partly due to the vastly different plasma beta between
the photosphere and the corona. Better results in understanding
the coronal magnetic field should be derived from measurements of
the magnetic field in the chromosphere. To that end, we are pursuing
quantitative determination of the magnetic field in the chromosphere,
where plasma beta transitions from greater than unity to less than
unity, via ultraviolet spectropolarimetry. The CLASP2 mission, flown
on a sounding rocket in April 2019, succeeded in measuring all four
Stokes polarization parameters in UV spectral lines formed by singly
ionized Magnesium and neutral Manganese. Because these ions produce
spectral lines under different conditions, CLASP2 thus was able to
quantify the magnetic field properties at multiple heights in the
chromosphere simultaneously, as shown in the recent paper by Ishikawa
et al. In this presentation we will report the findings of CLASP2,
demonstrating the variation of magnetic fields along a track on
the solar surface and as a function of height in the chromosphere;
and we will illustrate what is next for the CLASP missions and the
demonstration of UV spectropolarimetry in the solar chromosphere.
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Title: Long Characteristics versus Short Characteristics in 3D
Radiative Transfer Simulations of Polarized Radiation
Authors: de Vicente, A.; del Pino Alemán, T.; Trujillo Bueno, J.
2021ApJ...912...63D Altcode: 2021arXiv210304065D
We compare maps of scattering polarization signals obtained
from three-dimensional (3D) radiation transfer calculations in a
magnetoconvection model of the solar atmosphere using formal solvers
based on the "short characteristics" (SC) and the "long characteristics"
(LC) methods. The SC method requires less computational work, but
it is known to introduce spatial blurring in the emergent radiation
for inclined lines of sight. For polarized radiation this effect
is generally more severe due to it being a signed quantity and
to the sensitivity of the scattering polarization to the model's
inhomogeneities. We study the differences in the polarization signals
of the emergent spectral line radiation calculated with such formal
solvers. We take as a case study already published results of the
scattering polarization in the Sr I 4607 Å line obtained with the SC
method, demonstrating that in high-resolution grids it is accurate
enough for that type of study. In general, the LC method is the
preferred one for accurate calculations of the emergent radiation,
which is the reason why it is now one of the options in the public
version of the 3D radiative transfer code PORTA.
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Title: Evaluating the Reliability of a Simple Method to Map the
Magnetic Field Azimuth in the Solar Chromosphere
Authors: Jurčák, Jan; Štěpán, Jiří; Trujillo Bueno, Javier
2021ApJ...911...23J Altcode: 2021arXiv210202880J
The Zeeman effect is of limited utility for probing the magnetism
of the quiet solar chromosphere. The Hanle effect in some spectral
lines is sensitive to such magnetism, but the interpretation of the
scattering polarization signals requires taking into account that the
chromospheric plasma is highly inhomogeneous and dynamic (i.e., that
the magnetic field is not the only cause of symmetry breaking). Here
we investigate the reliability of a well-known formula for mapping the
azimuth of chromospheric magnetic fields directly from the scattering
polarization observed in the Ca II 8542 Å line, which is typically
in the saturation regime of the Hanle effect. To this end, we use
the Stokes profiles of the Ca II 8542 Å line computed with the PORTA
radiative transfer code in a three-dimensional (3D) model of the solar
chromosphere, degrading them to mimic spectropolarimetric observations
for a range of telescope apertures and noise levels. The simulated
observations are used to obtain the magnetic field azimuth at each
point of the field of view, which we compare with the actual values
within the 3D model. We show that, apart from intrinsic ambiguities,
the method provides solid results. Their accuracy depends more on
the noise level than on the telescope diameter. Large-aperture solar
telescopes, like DKIST and EST, are needed to achieve the required
polarimetric sensitivity using reasonable exposure times.
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Title: The Impact of Limited Time Resolution on the Forward-scattering
Polarization in the Solar Sr I 4607 Å Line
Authors: del Pino Alemán, T.; Trujillo Bueno, J.
2021ApJ...909..180D Altcode: 2021ApJ...909..180P; 2021arXiv210108485D
Theoretical investigations predicted that high spatiotemporal resolution
observations in the Sr I 4607 Å line must show a conspicuous
scattering polarization pattern at the solar disk center, which
encodes information on the unresolved magnetism of the intergranular
photospheric plasma. Here we present a study of the impact of limited
time resolution on the observability of such forward-scattering
(disk-center) polarization signals. Our investigation is based on
three-dimensional radiative transfer calculations in a time-dependent
magnetoconvection model of the quiet solar photosphere, taking into
account anisotropic radiation pumping and the Hanle effect. This type of
radiative transfer simulation is computationally costly, which is why
the time variation had not been investigated before for this spectral
line. We compare our theoretical results with recent disk-center
filter polarimetric observations in the Sr I 4607 Å line, showing
that there is good agreement in the polarization patterns. We also show
what we can expect to observe with the Visible Spectro-Polarimeter at
the upcoming Daniel K. Inouye Solar Telescope.
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Title: The Effects of Three-dimensional Radiative Transfer on the
Resonance Polarization of the Ca I 4227 Å Line
Authors: Jaume Bestard, J.; Trujillo Bueno, J.; Štěpán, J.; del
Pino Alemán, T.
2021ApJ...909..183J Altcode: 2021arXiv210104421J
The sizable linear polarization signals produced by the scattering of
anisotropic radiation in the core of the Ca I 4227 Å line constitute
an important observable for probing the inhomogeneous and dynamic
plasma of the lower solar chromosphere. Here we show the results
of a three-dimensional (3D) radiative transfer complete frequency
redistribution investigation of the line's scattering polarization
in a magnetohydrodynamical 3D model of the solar atmosphere. We
take into account not only the Hanle effect produced by the model's
magnetic field but also the symmetry breaking caused by the horizontal
inhomogeneities and macroscopic velocity gradients. The spatial
gradients of the horizontal components of the macroscopic velocities
produce very significant forward scattering polarization signals
without the need of magnetic fields, while the Hanle effect tends to
depolarize them at the locations where the model's magnetic field is
stronger than about 5 G. The standard 1.5D approximation is found to
be unsuitable for understanding the line's scattering polarization,
but we introduce a novel improvement to this approximation that
produces results in qualitative agreement with the full 3D results. The
instrumental degradation of the calculated polarization signals is also
investigated, showing what we can expect to observe with the Visible
Spectro-Polarimeter at the upcoming Daniel K. Inouye Solar Telescope.
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Title: Magnetic Imaging of the Outer Solar Atmosphere (MImOSA):
Unlocking the driver of the dynamics in the upper solar atmosphere
Authors: Peter, H.; Alsina Ballester, E.; Andretta, V.; Auchere, F.;
Belluzzi, L.; Bemporad, A.; Berghmans, D.; Buchlin, E.; Calcines, A.;
Chitta, L. P.; Dalmasse, K.; del Pino Aleman, T.; Feller, A.; Froment,
C.; Harrison, R.; Janvier, M.; Matthews, S.; Parenti, S.; Przybylski,
D.; Solanki, S. K.; Stepan, J.; Teriaca, L.; Trujillo Bueno, J.
2021arXiv210101566P Altcode:
The magnetic activity of the Sun directly impacts the Earth and human
life. Likewise, other stars will have an impact on the habitability
of planets orbiting these host stars. The lack of information on the
magnetic field in the higher atmospheric layers hampers our progress in
understanding solar magnetic activity. Overcoming this limitation would
allow us to address four paramount long-standing questions: (1) How
does the magnetic field couple the different layers of the atmosphere,
and how does it transport energy? (2) How does the magnetic field
structure, drive and interact with the plasma in the chromosphere and
upper atmosphere? (3) How does the magnetic field destabilise the outer
solar atmosphere and thus affect the interplanetary environment? (4)
How do magnetic processes accelerate particles to high energies? New
ground-breaking observations are needed to address these science
questions. We suggest a suite of three instruments that far exceed
current capabilities in terms of spatial resolution, light-gathering
power, and polarimetric performance: (a) A large-aperture UV-to-IR
telescope of the 1-3 m class aimed mainly to measure the magnetic
field in the chromosphere by combining high spatial resolution and high
sensitivity. (b) An extreme-UV-to-IR coronagraph that is designed to
measure the large-scale magnetic field in the corona with an aperture
of about 40 cm. (c) An extreme-UV imaging polarimeter based on a 30
cm telescope that combines high throughput in the extreme UV with
polarimetry to connect the magnetic measurements of the other two
instruments. This mission to measure the magnetic field will unlock
the driver of the dynamics in the outer solar atmosphere and thereby
greatly advance our understanding of the Sun and the heliosphere.
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Title: Improved near optimal angular quadratures for polarised
radiative transfer in 3D MHD models
Authors: Jaume Bestard, Jaume; Štěpán, Jiří; Trujillo Bueno,
Javier
2021A&A...645A.101J Altcode: 2020arXiv201204981J
Accurate angular quadratures are crucial for the numerical solution
of three-dimensional (3D) radiative transfer problems, especially
when the spectral line polarisation produced by the scattering of
anisotropic radiation is included. There are two requirements for
obtaining an optimal quadrature and they are difficult to satisfy
simultaneously: high accuracy and short computing time. By imposing
certain symmetries, we were recently able to derive a set of near
optimal angular quadratures. Here, we extend our previous investigation
by considering other symmetries. Moreover, we test the performance of
our new quadratures by numerically solving a radiative transfer problem
of resonance line polarisation in a 3D model of the solar atmosphere
resulting from a magneto-hydrodynamical simulation. The new angular
quadratures derived here outperform the previous ones in terms of the
number of rays needed to achieve any given accuracy. <P />The tables
mentioned in Sect. 4 are only available at the CDS via anonymous ftp to
<A href="http://cdsarc.u-strasbg.fr/">http://cdsarc.u-strasbg.fr</A>
(ftp://130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/645/A101">http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/645/A101</A>
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Title: Optical design of the Chromospheric LAyer Spectro-Polarimeter
(CLASP2)
Authors: Tsuzuki, Toshihiro; Ishikawa, Ryohko; Kano, Ryouhei; Narukage,
Noriyuki; Song, Donguk; Yoshida, Masaki; Uraguchi, Fumihiro; Okamoto,
Takenori J.; McKenzie, David; Kobayashi, Ken; Rachmeler, Laurel;
Auchere, Frederic; Trujillo Bueno, Javier
2020SPIE11444E..6WT Altcode:
Chromospheric LAyer Spectro-Polarimeter (CLASP2) was a sounding
rocket experiment, which is a follow-up mission to the Chromospheric
Lyman-Alpha Spectro-Polarimeter (CLASP1) in 2015. To measure the
magnetic fields in the upper solar atmosphere in a highly quantitative
manner, CLASP2 changes the target wavelengths from the hydrogen Ly-α
line (121.567 nm) to Mg II lines near 280 nm. We reused the main
structure and most of the optical components in the CLASP1 instrument,
which reduced the turnaround time and cost. We added a magnifying
optical system to maintain the wavelength resolution, even at the
longer wavelength of CLASP2. Here, we describe the optical design and
performance of the CLASP2 instrument.
---------------------------------------------------------
Title: VizieR Online Data Catalog: 3D MHD models angular quadratures
(Jaume Bestard+, 2021)
Authors: Jaume Bestard, J.; Stepan, J.; Trujillo Bueno, J.
2020yCat..36450101J Altcode:
The file name has the following convention: u: quadrature for
unpolarised radiation p: quadrature for polarised radiation lX:
quadrature for the order L=X nY: quadrature with N=Y rays in total. All
the files have the same structure. <P />(28 data files).
---------------------------------------------------------
Title: The polarization of the Hα line in the quiet solar
chromosphere
Authors: Jaume Bestard, J.; Trujillo Bueno, J.; Štěpán, J.; Bianda,
M.; Ramelli, R.
2020sea..confE.200J Altcode:
One-dimensional radiative transfer (RT) calculations suggested that the
scattering polarization profiles of the Hα line are very sensitive to
the strength and structure of the chromospheric magnetic field. Here
we present unprecedented spectropolarimetric observations of the Hα
line obtained with ZIMPOL-3 at IRSOL. The linear polarization profiles
show a rich variety of shapes and amplitudes, as well as an interesting
spatial variability. We confront them with the theoretical scattering
polarization profiles we have obtained by solving the complex RT problem
of the Hα polarization in a 3D model from MHD simulations, highlighting
the impact produced by the model's magnetic and velocity field. This
investigation reveals the great interest of the Hα polarization in
the present new era of large-aperture solar telescopes.
---------------------------------------------------------
Title: Near optimal angular quadratures for polarised radiative
transfer
Authors: Štěpán, Jiří; Jaume Bestard, Jaume; Trujillo Bueno,
Javier
2020A&A...636A..24S Altcode: 2020arXiv200212736S
In three-dimensional (3D) radiative transfer (RT) problems, the
tensor product quadratures are generally not optimal in terms of
the number of discrete ray directions needed for a given accuracy
of the angular integration of the radiation field. In this paper, we
derive a new set of angular quadrature rules that are more suitable
for solving 3D RT problems with the short- and long-characteristics
formal solvers. These quadratures are more suitable than the currently
used ones for the numerical calculation of the radiation field tensors
that are relevant in the problem of the generation and transfer of
polarised radiation without assuming local thermodynamical equilibrium
(non-LTE). We show that our new quadratures can save up to about 30%
of computing time with respect to the Gaussian-trapezoidal product
quadratures with the same accuracy. <P />The tables mentioned in
Appendix A are only available at the CDS via anonymous ftp to <A
href="http://cdsarc.u-strasbg.fr/">http://cdsarc.u-strasbg.fr</A>
(ftp://130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/636/A24">http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/636/A24</A>
---------------------------------------------------------
Title: The Magnetic Sensitivity of the Resonance and Subordinate
Lines of Mg II in the Solar Chromosphere
Authors: del Pino Alemán, T.; Trujillo Bueno, J.; Casini, R.; Manso
Sainz, R.
2020ApJ...891...91D Altcode: 2020arXiv200409176D
We carry out a theoretical study of the polarization of the solar Mg
II h-k doublet (including its extended wings) and the subordinate
ultraviolet (UV) triplet around 280 nm. These lines are of great
diagnostic interest, as they encode information on the physical
properties of the solar atmosphere from the upper photosphere to the
chromosphere-corona transition region. We base our study on radiative
transfer calculations of spectral line polarization in one-dimensional
models of quiet and plage regions of the solar atmosphere. Our
calculations take into account the combined action of atomic
polarization, quantum level interference, frequency redistribution,
and magnetic fields of arbitrary strength. In particular, we study the
sensitivity of the emergent Stokes profiles to changes in the magnetic
field through the Zeeman and Hanle effects. We also study the impact
of the chromospheric plasma dynamics on the emergent Stokes profiles,
taking into account the angle-dependent frequency redistribution in the
h-k resonance transitions. The results presented here are of interest
for the interpretation of spectropolarimetric observations in this
important region of the solar UV spectrum.
---------------------------------------------------------
Title: VizieR Online Data Catalog: Polarised radiative transfer
angular quadratures (Stepan+, 2020)
Authors: Stepan, J.; Jaume Bestard, J.; Trujillo Bueno, J.
2020yCat..36360024S Altcode:
Quadrature for unpolarised and polarised radiations. <P />(13 data
files).
---------------------------------------------------------
Title: The Chromospheric Layer Spectro-Polarimeter (CLASP2) Sounding
Rocket Mission: First Results
Authors: McKenzie, D. E.; Ishikawa, R.; Trujillo Bueno, J.; Auchere,
F.; Rachmeler, L.; Kano, R.; Song, D.; Okamoto, J.; Kobayashi, K.;
Yoshida, M.
2019AGUFMSH44A..06M Altcode:
A major challenge for heliophysics is to decipher the magnetic structure
of the chromosphere, because of its vital role in the transport of
energy into the corona and solar wind. Routine satellite measurements
of the chromospheric magnetic field will dramatically improve our
understanding of the chromosphere and its connection to the rest of
the solar atmosphere. Before such a satellite can be considered for
flight, we must refine the measurement techniques by exploring emission
lines with a range of magnetic sensitivities. In 2015, CLASP achieved
the first measurement of linear polarization produced by scattering
processes in a far UV resonance line (hydrogen Lyman-α), and the
first exploration of the magnetic field (via the Hanle effect) and
geometrical complexity in quiet regions of the chromosphere/corona
transition region. These measurements are a first step towards
routine quantitative characterization of the local thermal and magnetic
conditions in this key layer of the solar atmosphere. <P />Nonetheless,
Lyman-α is only one of the magnetically sensitive spectral lines in
the UV spectrum. CLASP2 extends the capability of UV spectropolarimetry
by acquiring groundbreaking measurements in the Mg II h and k spectral
lines near 280 nm, whose cores form about 100 km below the Lyman-α
core. These lines are sensitive to a larger range of field strengths
than Lyman-α, through both the Hanle and Zeeman effects. CLASP2
captures measurements of linear and circular polarization to enable
the first determination of all 4 Stokes parameters in chromospheric
UV radiation. Coupled with numerical modeling of the observed spectral
line polarization (anisotropic radiation pumping with Hanle, Zeeman and
magneto-optical effects), CLASP2 is a pathfinder for determination
of the magnetic field's strength and direction, as well as of the
geometry of the plasma in the upper solar chromosphere. <P />CLASP2
was launched from White Sands Missile Range in April 2019. In this
presentation, we will summarize the characteristics of the CLASP2
flight, the performance of the UV telescope and spectropolarimeter,
and our preliminary findings.
---------------------------------------------------------
Title: Center-to-Limb Variation of the polarization of Mg II h &
k lines as measured by CLASP2
Authors: Rachmeler, L.; McKenzie, D. E.; Ishikawa, R.; Kano, R.;
Trujillo Bueno, J.; Kobayashi, K.; Song, D.; Yoshida, M.; Auchere,
F.; Okamoto, J.
2019AGUFMSH11D3380R Altcode:
The Chromospheric LAyer SpectroPolarimeter 2 (CLASP2) is a sounding
rocket that was launched from White Sands Missile Range in April
2019. CLASP2 is a reflight of the CLASP instrument, and has been
modified to observe the polarization of the Magnesium II h & k
lines in the solar chromosphere. The instrument contains a slit-jaw
context imager at Lyman Alpha (~121.6nm) and two spectropolarimetric
cameras that capture Mg II h & k near 280nm. A rotating polarization
modulation unit allows us to capture the full polarization state of
Mg II h & k; the measured polarization signals are sensitive
to the Hanle and the Zeeman magnetic effects, and magneto-optical
effects. The center-to-limb variations (CLV) of the intensity of
these lines has been measured, but the CLV of the polarization signals
has only been investigated theoretically. The first flight of CLASP,
which measured the linear polarization of the Lyman alpha line, found
a surprising lack of CLV in the line core (Kano et al. 2017), which
has important implications for the magnetic strength and geometrical
complexity of the chromosphere-corona transition region (Trujillo Bueno
et al. 2018). We present here initial results on the CLV of the Mg II
polarization signals.
---------------------------------------------------------
Title: Science Requirement Document (SRD) for the European Solar
Telescope (EST) (2nd edition, December 2019)
Authors: Schlichenmaier, R.; Bellot Rubio, L. R.; Collados, M.;
Erdelyi, R.; Feller, A.; Fletcher, L.; Jurcak, J.; Khomenko, E.;
Leenaarts, J.; Matthews, S.; Belluzzi, L.; Carlsson, M.; Dalmasse,
K.; Danilovic, S.; Gömöry, P.; Kuckein, C.; Manso Sainz, R.;
Martinez Gonzalez, M.; Mathioudakis, M.; Ortiz, A.; Riethmüller,
T. L.; Rouppe van der Voort, L.; Simoes, P. J. A.; Trujillo Bueno,
J.; Utz, D.; Zuccarello, F.
2019arXiv191208650S Altcode:
The European Solar Telescope (EST) is a research infrastructure
for solar physics. It is planned to be an on-axis solar telescope
with an aperture of 4 m and equipped with an innovative suite of
spectro-polarimetric and imaging post-focus instrumentation. The EST
project was initiated and is driven by EAST, the European Association
for Solar Telescopes. EAST was founded in 2006 as an association
of 14 European countries. Today, as of December 2019, EAST consists
of 26 European research institutes from 18 European countries. The
Preliminary Design Phase of EST was accomplished between 2008 and
2011. During this phase, in 2010, the first version of the EST Science
Requirement Document (SRD) was published. After EST became a project
on the ESFRI roadmap 2016, the preparatory phase started. The goal
of the preparatory phase is to accomplish a final design for the
telescope and the legal governance structure of EST. A major milestone
on this path is to revisit and update the Science Requirement Document
(SRD). The EST Science Advisory Group (SAG) has been constituted by
EAST and the Board of the PRE-EST EU project in November 2017 and has
been charged with the task of providing with a final statement on the
science requirements for EST. Based on the conceptual design, the SRD
update takes into account recent technical and scientific developments,
to ensure that EST provides significant advancement beyond the current
state-of-the-art. The present update of the EST SRD has been developed
and discussed during a series of EST SAG meetings. The SRD develops
the top-level science objectives of EST into individual science
cases. Identifying critical science requirements is one of its main
goals. Those requirements will define the capabilities of EST and the
post-focus instrument suite. The technical requirements for the final
design of EST will be derived from the SRD.
---------------------------------------------------------
Title: High-frequency Wave Propagation Along a Spicule Observed
by CLASP
Authors: Yoshida, Masaki; Suematsu, Yoshinori; Ishikawa, Ryohko;
Okamoto, Takenori J.; Kubo, Masahito; Kano, Ryouhei; Narukage,
Noriyuki; Bando, Takamasa; Winebarger, Amy R.; Kobayashi, Ken;
Trujillo Bueno, Javier; Auchère, Frédéric
2019ApJ...887....2Y Altcode:
The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) sounding
rocket experiment, launched in 2015 September, observed the hydrogen
Lyα line (121.6 nm) in an unprecedented high temporal cadence of
0.3 s. CLASP performed sit-and-stare observations of the quiet Sun
near the limb for 5 minutes with a slit perpendicular to the limb
and successfully captured an off-limb spicule evolving along the
slit. The Lyα line is well suited for investigating how spicules
affect the corona because it is sensitive to higher temperatures than
other chromospheric lines, owing to its large optical thickness. We
found high-frequency oscillations of the Doppler velocity with periods
of 20-50 s and low-frequency oscillation of periods of ∼240 s on
the spicule. From a wavelet analysis of the time sequence data of
the Doppler velocity, in the early phase of the spicule evolution,
we found that waves with a period of ∼30 s and a velocity amplitude
of 2-3 km s<SUP>-1</SUP> propagated upward along the spicule with a
phase velocity of ∼470 km s<SUP>-1</SUP>. In contrast, in the later
phase, possible downward and standing waves with smaller velocity
amplitudes were also observed. The high-frequency waves observed in
the early phase of the spicule evolution would be related with the
dynamics and the formation of the spicules. Our analysis enabled us to
identify the upward, downward, and standing waves along the spicule
and to obtain the velocity amplitude of each wave directly from the
Doppler velocity for the first time. We evaluated the energy flux
by the upward-propagating waves along the spicule, and discussed the
impact to the coronal heating.
---------------------------------------------------------
Title: PolStar - An Explorer-Class FUV Spectropolarimetry Mission
to Map the Environments of Massive Stars
Authors: Scowen, Paul; Ignace, Richard; Neiner, Coralie; Wade, Gregg;
Beasley, Matt; Bjorkman, Jon; Bouret, Jean-Claude; Casini, Roberto;
del Pino Alemán, Tanausu; Edgington, Samantha; Gayley, Ken; Guinan,
Ed; Hoffman, Jennifer; Howarth, Ian; Hull, Tony; Manso Sainz, Rafael;
Naze, Yael; Nordt, Alison; Owocki, Stan; Petrinec, Steve; Prinja,
Raman; Sana, Hugues; Shultz, Matt; Sparks, William; St-Louis, Nicole;
Tillier, Clem; Trujillo Bueno, Javier; Vasudevan, Gopal; Woodruff, Bob
2019BAAS...51g.167S Altcode: 2019astro2020U.167S; 2019arXiv191106724S
PolStar is an Explorer-class far ultraviolet (FUV) spectropolarimetry
mission designed to target massive stars and their environments. PolStar
will take advantage of resonance lines only available in the FUV to
measure for the first time the magnetic and wind environment around
massive stars to constrain models of rotation and mass loss.
---------------------------------------------------------
Title: The diagnostic potential of the weak field approximation for
investigating the quiet Sun magnetism: the Si I 10 827 Å line
Authors: Shchukina, N. G.; Trujillo Bueno, J.
2019A&A...628A..47S Altcode:
<BR /> Aims: We aim to investigate the validity of the weak field
approximation (WFA) for determining magnetic fields in quiet regions
of the solar photosphere using the polarization caused by the Zeeman
effect in the Si I 10 827 Å line. <BR /> Methods: We solved the NLTE
line formation problem by means of multilevel radiative transfer
calculations in a three-dimensional (3D) snapshot model taken from
a state-of-the-art magneto-convection simulation of the small-scale
magnetic activity in the quiet solar photosphere. The 3D model
used is characterized by a surface mean magnetic field strength of
about 170 G. The calculated Stokes profiles were degraded because
of the atmospheric turbulence of Earth and light diffraction by the
telescope aperture. We apply the WFA to the Stokes I, Q, U, V profiles
calculated for different seeing conditions and for the apertures of
the VTT, GREGOR, EST and DKIST telescopes. We compare the inferred
longitudinal and transverse components of the magnetic field with
the original vertical and horizontal fields of the 3D model. <BR />
Results: We find that with a spatial resolution significantly better
than 0.5″ the surface maps of the magnetic field inferred from
the Stokes profiles of the Si I 10 827 Å line applying the WFA are
close to the magnetic field of the model on the corrugated surface,
corresponding to line optical depth unity at Δλ ≈ 0.1 Å for a
disk-center line of sight. The correlation between them is relatively
high, except that the inferred longitudinal and transverse components
of the magnetic field turn out to be lower than in the 3D model. <BR />
Conclusions: The use of the WFA for interpreting high-spatial-resolution
spectropolarimetric observations of the Si I 10 827 Å line obtained
with telescopes like GREGOR, EST, and DKIST allows the longitudinal
and transverse components of the magnetic field to be retrieved with
reasonable precision over the whole quiet solar photosphere, the result
being worse for telescopes of lower aperture.
---------------------------------------------------------
Title: Magnetic Sensitivity in the Wing Scattering Polarization
Signals of the Hydrogen Lyman-α Line of the Solar Disk Radiation
Authors: Alsina Ballester, E.; Belluzzi, L.; Trujillo Bueno, J.
2019ApJ...880...85A Altcode: 2019arXiv190110994A
The linear polarization produced by scattering processes in the hydrogen
Lyα line of the solar disk radiation is a key observable for probing
the chromosphere-corona transition region (TR) and the underlying
chromospheric plasma. While the line-center signal encodes information
on the magnetic field and the three-dimensional structure of the TR,
the sizable scattering polarization signals that the joint action of
partial frequency redistribution and J-state interference produce in
the Lyα wings have generally been thought to be sensitive only to the
thermal structure of the solar atmosphere. Here we show that the wings
of the Q/I and U/I scattering polarization profiles of this line are
actually sensitive to the presence of chromospheric magnetic fields,
with strengths similar to those that produce the Hanle effect in the
line core (i.e., between 5 and 100 G, approximately). In spite of the
fact that the Zeeman splitting induced by such weak fields is very
small compared to the total width of the line, the magneto-optical
effects that couple the transfer equations for Stokes Q and U are
actually able to produce sizable changes in the Q/I and U/I wings. We
find that magnetic fields with longitudinal components larger than 100
G produce an almost complete depolarization of the wings of the Lyα
Q/I profiles within a ±5 Å spectral range around the line center,
while stronger fields are required for the U/I wing signals to be
depolarized to a similar extent. The theoretical results presented
here further expand the diagnostic content of the unprecedented
spectropolarimetric observations provided by the Chromospheric
Lyman-Alpha Spectro-Polarimeter.
---------------------------------------------------------
Title: The Chromospheric Layer Spectro-Polarimeter (CLASP2) Sounding
Rocket Mission: First Results
Authors: McKenzie, David Eugene; Ishikawa, Ryohko; Kano, Ryouhei;
Rachmeler, Laurel; Trujillo Bueno, Javier; Kobayashi, Ken; Song,
Donguk; Yoshida, Masaki; Auchere, Frederic; Okamoto, Takenori
2019AAS...23412601M Altcode:
A major challenge for heliophysics is to decipher the magnetic structure
of the chromosphere, because of its vital role in the transport of
energy into the corona and solar wind. Routine satellite measurements
of the chromospheric magnetic field will dramatically improve our
understanding of the chromosphere and its connection to the rest of
the solar atmosphere. Before such a satellite can be considered for
flight, we must refine the measurement techniques by exploring emission
lines with a range of magnetic sensitivities. In 2015, CLASP achieved
the first measurement of linear polarization produced by scattering
processes in a far UV resonance line (hydrogen Lyman-α), and the
first exploration of the magnetic field (via the Hanle effect) and
geometrical complexity in quiet regions of the chromosphere-corona
transition region. These measurements are a first step towards
routine quantitative characterization of the local thermal and magnetic
conditions in this key layer of the solar atmosphere. <P />Nonetheless,
Lyman-α is only one of the magnetically sensitive spectral lines in the
UV spectrum. CLASP2 extends the capability of UV spectropolarimetry by
acquiring ground-breaking measurements in the Mg II h and k spectral
lines near 280 nm, whose cores form about 100 km below the Lyman-α
core. These lines are sensitive to a larger range of field strengths
than Lyman-α, through both the Hanle and Zeeman effects. CLASP2 will
capture measurements of linear and circular polarization to enable the
first determination of all 4 Stokes parameters in chromospheric UV
radiation. Coupled with numerical modeling of the observed spectral
line polarization (anisotropic radiation pumping with Hanle, Zeeman
and magneto-optical effects), CLASP2 is a pathfinder for determination
of the magnetic field's strength and direction, as well as of the
geometry of the plasma in the upper solar chromosphere. <P />CLASP2
will launch from White Sands Missile Range in April 2019. In this
presentation, we will summarize the characteristics of the CLASP2
flight, the performance of the UV telescope and spectropolarimeter,
and our preliminary findings.
---------------------------------------------------------
Title: Lyman-α imaging polarimetry with the CLASP2 sounding rocket
mission
Authors: Kano, Ryouhei; Ishikawa, Ryohko; McKenzie, David Eugene;
Trujillo Bueno, Javier; Song, Donguk; Yoshida, Masaki; Okamoto,
Takenori; Rachmeler, Laurel; Kobayashi, Ken; Auchere, Frederic
2019AAS...23430216K Altcode:
Ultraviolet polarimetry offers a unique opportunity to explore the upper
solar chromosphere and the transition region (TR) to the million-degree
corona. These outer atmospheric regions play a key role in the transfer
of mass and energy from the solar photosphere to the corona. With
a sounding rocket experiment called the Chromospheric Lyman-Alpha
Spectro-Polarimeter (CLASP), in September 2015 we succeeded in obtaining
the first measurement of the linear polarization produced by scattering
processes in the hydrogen Lyman-α line of the solar disk radiation. The
analysis and interpretation of such spectro-polarimetric observation
allowed us to obtain information on the geometrical complexity of
the corrugated surface that delineates the TR, as well as on the
magnetic field strength via the Hanle effect. At the same time, the
CLASP slit-jaw (SJ) optics system, which is a Lyman-α filter imager
characterized by a FWHM= 7 nm, allowed us to obtain broad-band Stokes-I
and Q/I images over a large field of view. The obtained broad-band
Q/I images are dominated by the scattering polarization signals of the
Lyman-α wings, and not by the much weaker line-center signals where
the Hanle effect operates. Recently, Alsina Ballester et al. (2019,
ApJ, in press) showed that the scattering polarization signals of the
Lyman-α wings are sensitive to chromospheric magnetic fields via the
magneto-optical effects. Therefore, Lyman-α imaging polarimetry is of
scientific interest also for magnetic-field investigations. On April
11, 2019, we performed another sounding rocket experiment, called
the Chromospheric LAyer Spectro-Polarimeter (CLASP2). We used the
same instrument after significant modifications in order to obtain
spectro-polarimetric observations of a plage and a quiet region in
the ionized magnesium lines around 280 nm (i.e., the Mg II h &
k lines). At the same time, the CLASP2 SJ optics system allowed us to
obtain broad-band Q/I and U/I images at the Lyman-α wavelength, in
addition to the well-known SJ intensity images. In this presentation,
we provide a first overview of the CLASP2 SJ data.
---------------------------------------------------------
Title: Modeling the Scattering Polarization of the Hydrogen Lyα
Line Observed by CLASP in a Filament Channel
Authors: Štěpán, J.; Trujillo Bueno, J.; Gunár, S.; Heinzel, P.;
del Pino Alemán, T.; Kano, R.; Ishikawa, R.; Narukage, N.; Bando,
T.; Winebarger, A.; Kobayashi, K.; Auchère, F.
2019ASPC..526..165S Altcode:
The 400 arcsec spectrograph slit of CLASP crossed mainly quiet
regions of the solar chromosphere, from the limb towards the solar
disk center. Interestingly, in the CLASP slit-jaw images and in the
SDO images of the He II line at 304 Å, we can identify a filament
channel (FC) extending over more than 60 arcsec crossing the slit of
the spectrograph. In order to interpret the peculiar spatial variation
of the Q/I and U/I signals observed by CLASP in the hydrogen Lyα line
(1216 Å), we perform multi-dimensional radiative transfer modeling
in given filament models. In this contribution, we show the first
results of the two-dimensional calculations we have carried out, with
the aim of determining the filament thermal and magnetic structure by
comparing the theoretical and the observed polarization signals. Our
results suggest that the temperature gradients in the filament observed
by CLASP are significantly larger than previously thought.
---------------------------------------------------------
Title: CLASP2: The Chromospheric LAyer Spectro-Polarimeter
Authors: McKenzie, D. E.; Ishikawa, R.; Trujillo Bueno, J.; Auchére,
F.; Rachmeler, L. A.; Kubo, M.; Kobayashi, K.; Winebarger, A. R.;
Bethge, C. W.; Narukage, N.; Kano, R.; Ishikawa, S.; de Pontieu,
B.; Carlsson, M.; Yoshida, M.; Belluzzi, L.; Štěpán, J.; del Pino
Alemán, T.; Alsina Ballester, E.; Asensio Ramos, A.
2019ASPC..526..361M Altcode:
The hydrogen Lyman-α line at 121.6 nm and the Mg k line at 279.5
nm are especially relevant for deciphering the magnetic structure
of the chromosphere since their line-center signals are formed in
the chromosphere and transition region, with unique sensitivities to
magnetic fields. We propose the Chromospheric LAyer Spectro-Polarimeter
(CLASP2), to build upon the success of the first CLASP flight, which
measured the linear polarization in H I Lyman-α. The existing CLASP
instrument will be refitted to measure all four Stokes parameters in
the 280 nm range, including variations due to the anisotropic radiation
pumping, the Hanle effect, and the Zeeman effect.
---------------------------------------------------------
Title: A Quantitative Comparison of Observed and Theoretical Stokes
Profiles of the Ca II 8542 Å Line in the Quiet Sun
Authors: Jurčák, J.; Stěpán, J.; Bianda, M.; Trujillo Bueno, J.
2019ASPC..526..235J Altcode:
We present an analysis of the Stokes profiles of the Ca II 8542 Å
line produced by the joint action of atomic level polarization and the
Hanle and Zeeman effects. We compare spectropolarimetric observations
of this line in a quiet region at the solar disk centre, taken with
the ZIMPOL instrument at IRSOL, with the theoretical Stokes profiles
computed with the PORTA radiative transfer code using as solar model
atmosphere a 3D snapshot taken from a radiation MHD simulation of
an enhanced-network region. Even though the spatial sampling of the
ZIMPOL observations is only 1.43 arcsec/pixel, we detect Q/I, U/I and
V/I polarization signals of the order of 0.1%. The synthetic line
profiles have been obtained by solving the full 3D NLTE radiative
transfer problem taking into account the symmetry breaking effects
due to the model's horizontal inhomogeneities and macroscopic velocity
gradients. After spatial and spectral degradation, in some locations
we find similar amplitudes between the observed and calculated linear
polarization profiles. However, in general, the observations show
stronger polarization signals than the calculated ones, a discrepancy
that could be used to refine the numerical models of the quiet solar
chromosphere.
---------------------------------------------------------
Title: The Transfer of Resonance Line Polarization with PRD in the
General Hanle-Zeeman Regime
Authors: Alsina Ballester, E.; Belluzzi, L.; Trujillo Bueno, J.
2019ASPC..526..119A Altcode:
We present numerical radiative transfer calculations of the four
Stokes parameters of the radiation emerging from one-dimensional model
atmospheres. In this investigation we account for the impact of partial
frequency redistribution (PRD) in scattering and the joint action of
the Hanle and Zeeman effects. Strong resonance lines of interest for
chromospheric magnetic field diagnostics have been considered, namely
the Ca I line at 4227 Å and the Mg II k line at 2795 Å. The Stokes
profiles of these lines have been obtained by considering two-level
atomic models, both in the absence and in the presence of magnetic
fields. We draw attention to the fact that the magneto-optical
terms of the transfer equations for Stokes Q and U are responsible
for an interesting and previously unnoticed magnetic sensitivity of
their scattering polarization profiles beyond the Doppler core. This
important discovery contributes to paint a more detailed picture of the
influence of relatively weak magnetic fields on the observable linear
polarization signals of strong chromospheric lines, highlighting the
importance of a PRD treatment for such lines.
---------------------------------------------------------
Title: The Last Twenty Years. Optically Polarized Atoms in the
Solar Atmosphere
Authors: Trujillo Bueno, J.
2019ASPC..526...69T Altcode:
The 8th Solar Polarization Workshop in honor of Prof. Egidio
Landi Degl'Innocenti was a unique opportunity to review the last
twenty years of research on the generation and transfer of spectral
line polarization produced by optically pumped atoms in the solar
atmosphere. Many investigations have been carried out since 1997,
when Egidio and I published our first joint paper in The Astrophysical
Journal Letters, arguing that lower-level depopulation pumping is a key
physical mechanism for understanding some of the enigmatic spectral
features of the Second Solar Spectrum. Here I provide an overview of
the research carried out since then on optically polarized atoms in the
solar photosphere, chromosphere and transition region, with emphasis on
applications based on the quantum theory of spectral line polarization
to which Egidio contributed so many pioneering and fundamental results.
---------------------------------------------------------
Title: 3D Whole-Prominence Fine Structure Model as a Test Case for
Verification and Development of Magnetic Field Inversion Techniques
Authors: Gunár, S.; Mackay, D. H.; Štěpán, J.; Heinzel, P.;
Trujillo Bueno, J.
2019ASPC..526..159G Altcode:
We show the potential of a new 3D whole-prominence fine structure
model to serve as a well-controlled yet complex environment for testing
inversion techniques for the magnetic field inference. The realistic
3D magnetic field and plasma environment provided by the model can
be used for the direct synthesis of spectro-polarimetric data. Such
synthetic data can be analyzed by advanced inversion tools and their
results compared with the known properties provided by the model.
---------------------------------------------------------
Title: Solar Polarization Workshop 8
Authors: Belluzzi, L.; Casini, R.; Romoli, M.; Trujillo Bueno, J.
2019ASPC..526.....B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Comparison of Scattering Polarization Signals Observed by
CLASP: Possible Indication of the Hanle Effect
Authors: Ishikawa, R.; Trujillo Bueno, J.; Uitenbroek, H.; Kubo, M.;
Tsuneta, S.; Goto, M.; Kano, R.; Narukage, N.; Bando, T.; Katsukawa,
Y.; Ishikawa, S.; Giono, G.; Suematsu, Y.; Hara, H.; Shimizu, T.;
Sakao, T.; Winebarger, A.; Kobayashi, K.; Cirtain, J.; Champey, P.;
Auchère, F.; Štěpán, J.; Belluzzi, L.; Asensio Ramos, A.; Manso
Sainz, R.; De Pomtieu, B.; Ichimoto, K.; Carlsson, M.; Casini, R.
2019ASPC..526..305I Altcode:
The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP; Kano et
al. 2012; Kobayashi et al. 2012; Kubo et al. 2014) observed, for the
first time, the linear polarization produced by scattering processes
in the hydrogen Lyman-α (121.57 nm) and Si III (120.56 nm) lines of
the solar disk radiation. The complexity of the observed scattering
polarization (i.e., conspicuous spatial variations in Q/I and U/I
at spatial scales of 10″-20″ and the absence of center-to- limb
variation at the Lyman-α center; see Kano et al. 2017) motivated us
to search for possible hints of the operation of the Hanle effect by
comparing: (a) the Lyman-α line center signal, for which the critical
field strength (B<SUB>H</SUB>) for the onset of the Hanle effect is
53 G, (b) the Lyman-α wing, which is insensitive to the Hanle effect,
and (c) the Si III line, whose B<SUB>H</SUB> = 290 G. We focus on four
regions with different total unsigned photospheric magnetic fluxes
(estimated from SDO/HMI observations), and compare the corresponding
U/I spatial variations in the Lyman-α wing, Lyman-α center, and Si III
line. The U/I signal in the Lyman-α wing shows an antisymmetric spatial
distribution, which is caused by the presence of a bright structure in
all the selected regions, regardless of the total unsigned photospheric
magnetic flux. In an internetwork region, the Lyman-α center shows an
antisymmetric spatial variation across the selected bright structure,
but it does not show it in other more magnetized regions. In the Si III
line, the spatial variation of U/I deviates from the above-mentioned
antisymmetric shape as the total unsigned photospheric magnetic flux
increases. We argue that a plausible explanation of this differential
behavior is the operation of the Hanle effect. <P />This work, presented
in an oral contribution at this Workshop, has been published on The
Astrophysical Journal (Ishikawa et al. 2017).
---------------------------------------------------------
Title: Comparison of theoretical and observed Ca II 8542 Stokes
profiles in quiet regions at the centre of the solar disc
Authors: Jurčák, J.; Štěpán, J.; Trujillo Bueno, J.; Bianda, M.
2018A&A...619A..60J Altcode: 2018arXiv180809470J
Context. Interpreting the Stokes profiles observed in quiet regions
of the solar chromosphere is a challenging task. The Stokes Q and U
profiles are dominated by the scattering polarisation and the Hanle
effect, and these processes can only be correctly quantified if 3D
radiative transfer effects are taken into account. Forward-modelling
of the intensity and polarisation of spectral lines using a 3D model
atmosphere is a suitable approach in order to statistically compare
the theoretical and observed line profiles. <BR /> Aims: Our aim is to
present novel observations of the Ca II 8542 Å line profiles in a quiet
region at the centre of the solar disc and to quantitatively compare
them with the theoretical Stokes profiles obtained by solving the
problem of the generation and transfer of polarised radiation in a 3D
model atmosphere. We aim at estimating the reliability of the 3D model
atmosphere, excluding its known lack of dynamics and/or insufficient
density, using not only the line intensity but the full vector of
Stokes parameters. <BR /> Methods: We used data obtained with the
ZIMPOL instrument at the Istituto Ricerche Solari Locarno (IRSOL) and
compared the observations with the theoretical profiles computed with
the PORTA radiative transfer code, using as solar model atmosphere a
3D snapshot taken from a radiation-magnetohydrodynamics simulation. The
synthetic profiles were degraded to match the instrument and observing
conditions. <BR /> Results: The degraded theoretical profiles of the
Ca II 8542 line are qualitatively similar to the observed ones. We
confirm that there is a fundamental difference in the widths of all
Stokes profiles: the observed lines are wider than the theoretical
lines. We find that the amplitudes of the observed profiles are larger
than those of the theoretical ones, which suggests that the symmetry
breaking effects in the solar chromosphere are stronger than in the
model atmosphere. This means that the isosurfaces of temperature,
velocity, and magnetic field strength and orientation are more
corrugated in the solar chromosphere than in the currently available
3D radiation-magnetohydrodynamics simulation.
---------------------------------------------------------
Title: CLASP Constraints on the Magnetization and Geometrical
Complexity of the Chromosphere-Corona Transition Region
Authors: Trujillo Bueno, J.; Štěpán, J.; Belluzzi, L.; Asensio
Ramos, A.; Manso Sainz, R.; del Pino Alemán, T.; Casini, R.; Ishikawa,
R.; Kano, R.; Winebarger, A.; Auchère, F.; Narukage, N.; Kobayashi,
K.; Bando, T.; Katsukawa, Y.; Kubo, M.; Ishikawa, S.; Giono, G.; Hara,
H.; Suematsu, Y.; Shimizu, T.; Sakao, T.; Tsuneta, S.; Ichimoto, K.;
Cirtain, J.; Champey, P.; De Pontieu, B.; Carlsson, M.
2018ApJ...866L..15T Altcode: 2018arXiv180908865T
The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) is a
suborbital rocket experiment that on 2015 September 3 measured
the linear polarization produced by scattering processes in the
hydrogen Lyα line of the solar disk radiation. The line-center
photons of this spectral line radiation mostly stem from the
chromosphere-corona transition region (TR). These unprecedented
spectropolarimetric observations revealed an interesting surprise,
namely that there is practically no center-to-limb variation (CLV) in
the Q/I line-center signals. Using an analytical model, we first show
that the geometric complexity of the corrugated surface that delineates
the TR has a crucial impact on the CLV of the Q/I and U/I line-center
signals. Second, we introduce a statistical description of the solar
atmosphere based on a 3D model derived from a state-of-the-art radiation
magnetohydrodynamic simulation. Each realization of the statistical
ensemble is a 3D model characterized by a given degree of magnetization
and corrugation of the TR, and for each such realization we solve the
full 3D radiative transfer problem taking into account the impact
of the CLASP instrument degradation on the calculated polarization
signals. Finally, we apply the statistical inference method presented
in a previous paper to show that the TR of the 3D model that produces
the best agreement with the CLASP observations has a relatively weak
magnetic field and a relatively high degree of corrugation. We emphasize
that a suitable way to validate or refute numerical models of the upper
solar chromosphere is by confronting calculations and observations
of the scattering polarization in ultraviolet lines sensitive to the
Hanle effect.
---------------------------------------------------------
Title: A Statistical Inference Method for Interpreting the CLASP
Observations
Authors: Štěpán, J.; Trujillo Bueno, J.; Belluzzi, L.; Asensio
Ramos, A.; Manso Sainz, R.; del Pino Alemán, T.; Casini, R.; Kano, R.;
Winebarger, A.; Auchère, F.; Ishikawa, R.; Narukage, N.; Kobayashi,
K.; Bando, T.; Katsukawa, Y.; Kubo, M.; Ishikawa, S.; Giono, G.; Hara,
H.; Suematsu, Y.; Shimizu, T.; Sakao, T.; Tsuneta, S.; Ichimoto, K.;
Cirtain, J.; Champey, P.; De Pontieu, B.; Carlsson, M.
2018ApJ...865...48S Altcode: 2018arXiv180802725S
On 2015 September 3, the Chromospheric Lyman-Alpha SpectroPolarimeter
(CLASP) successfully measured the linear polarization produced by
scattering processes in the hydrogen Lyα line of the solar disk
radiation, revealing conspicuous spatial variations in the Q/I and U/I
signals. Via the Hanle effect, the line-center Q/I and U/I amplitudes
encode information on the magnetic field of the chromosphere-corona
transition region, but they are also sensitive to the three-dimensional
structure of this corrugated interface region. With the help of a simple
line-formation model, here we propose a statistical inference method
for interpreting the Lyα line-center polarization observed by CLASP.
---------------------------------------------------------
Title: A Novel Investigation of the Small-scale Magnetic Activity
of the Quiet Sun via the Hanle Effect in the Sr I 4607 Å Line
Authors: del Pino Alemán, T.; Trujillo Bueno, J.; Štěpán, J.;
Shchukina, N.
2018ApJ...863..164D Altcode: 2018arXiv180607293D
One of the key research problems in stellar physics is to decipher the
small-scale magnetic activity of the quiet solar atmosphere. Recent
magneto-convection simulations that account for small-scale dynamo
action have provided three-dimensional (3D) models of the solar
photosphere characterized by a high degree of small-scale magnetic
activity, similar to that found through theoretical interpretation of
the scattering polarization observed in the Sr I 4607 Å line. Here
we present the results of a novel investigation of the Hanle effect
in this resonance line based on 3D radiative transfer calculations
in a high-resolution magneto-convection model having most of
the convection zone magnetized close to the equipartition and a
surface mean field strength < B> ≈ 170 G. The Hanle effect
produced by the model’s magnetic field depolarizes the zero-field
scattering polarization signals significantly, to the extent that the
center-to-limb variation (CLV) of the calculated spatially averaged
polarization amplitudes is compatible with the observations. The
standard deviation of the horizontal fluctuations of the calculated
scattering polarization signals is very sensitive to the model’s
magnetic field, and we find that the predicted spatial variations
are sufficiently sizable so as to be able to detect them, especially
with the next generation of solar telescopes. We find that at all
on-disk positions, the theoretical scattering polarization signals are
anticorrelated with the continuum intensity. To facilitate reaching
new observational breakthroughs, we show how the theoretically
predicted polarization signals and spatial variations are modified
when deteriorating the signal-to-noise ratio and the spectral and
spatial resolutions of the simulated observations.
---------------------------------------------------------
Title: Current State of UV Spectro-Polarimetry and its Future
Direction
Authors: Ishikawa, Ryohko; Sakao, Taro; Katsukawa, Yukio; Hara,
Hirohisa; Ichimoto, Kiyoshi; Shimizu, Toshifumi; Kubo, Masahito;
Auchere, Frederic; De Pontieu, Bart; Winebarger, Amy; Kobayashi,
. Ken; Kano, Ryouhei; Narukage, Noriyuki; Trujillo Bueno, Javier;
Song, Dong-uk; Manso Sainz, Rafael; Asensio Ramos, Andres; Leenaarts,
Jorritt; Carlsson, Mats; Bando, Takamasa; Ishikawa, Shin-nosuke;
Tsuneta, Saku; Belluzzi, Luca; Suematsu, Yoshinori; Giono, Gabriel;
Yoshida, Masaki; Goto, Motoshi; Del Pino Aleman, Tanausu; Stepan,
Jiri; Okamoto, Joten; Tsuzuki, Toshihiro; Uraguchi, Fumihiro; Champey,
Patrick; Alsina Ballester, Ernest; Casini, Roberto; McKenzie, David;
Rachmeler, Laurel; Bethge, Christian
2018cosp...42E1564I Altcode:
To obtain quantitative information on the magnetic field in low beta
regions (i.e., upper chromosphere and above) has been increasingly
important to understand the energetic phenomena of the outer
solar atmosphere such as flare, coronal heating, and the solar wind
acceleration. In the UV range, there are abundant spectral lines that
originate in the upper chromosphere and transition region. However,
the Zeeman effect in these spectral lines does not give rise to easily
measurable polarization signals because of the weak magnetic field
strength and the larger Doppler broadening compared with the Zeeman
effect. Instead, the Hanle effect in UV lines is expected to be a
suitable diagnostic tool of the magnetic field in the upper atmospheric
layers. To investigate the validity of UV spectro-polarimetry and
the Hanle effect, the Chromospheric Lyman-Alpha Spectro-Polarimeter
(CLASP), which is a NASA sounding- rocket experiment, was launched at
White Sands in US on September 3, 2015. During its 5 minutes ballistic
flight, it successfully performed spectro-polarimetric observations
of the hydrogen Lyman-alpha line (121.57 nm) with an unprecedentedly
high polarization sensitivity of 0.1% in this wavelength range. CLASP
observed the linear polarization produced by scattering process in VUV
lines for the first time and detected the polarization signals which
indicate the operation of the Hanle effect. Following the success
of CLASP, we are confident that UV spectro-polarimetry is the way
to proceed, and we are planning the second flight of CLASP (CLASP2:
Chromospheric LAyer SpectroPolarimeter 2). For this second flight we
will carry out spectro-polarimetry in the Mg II h and k lines around
280 nm, with minimum modifications of the CLASP1 instrument. The linear
polarization in the Mg II k line is induced by scattering processes and
the Hanle effect, being sensitive to magnetic field strengths of 5 to 50
G. In addition, the circular polarizations in the Mg II h and k lines
induced by the Zeeman effect can be measurable in at least plage and
active regions. The combination of the Hanle and Zeeman effects could
help us to more reliably infer the magnetic fields of the upper solar
chromosphere. CLASP2 was selected for flight and is being developed for
launch in the spring of 2019.Based on these sounding rocket experiments
(CLASP1 and 2), we aim at establishing the strategy and refining the
instrument concept for future space missions to explore the enigmatic
atmospheric layers via UV spectro-polarimetry.
---------------------------------------------------------
Title: Wavefront error measurements and alignment of CLASP2 telescope
with a dual-band pass cold mirror coated primary mirror
Authors: Yoshida, Masaki; Song, Donguk; Ishikawa, Ryoko; Kano, Ryouhei;
Katsukawa, Yukio; Suematsu, Yoshinori; Narukage, Noriyuki; Kubo,
Masahito; Shinoda, Kazuya; Okamoto, Takenori J.; McKenzie, David E.;
Rachmeler, Laurel A.; Auchère, Frédéric; Trujillo Bueno, Javier
2018SPIE10699E..30Y Altcode:
"Chromospheric LAyer Spectro-Polarimeter (CLASP2)" is the next sounding
rocket experiment of the "Chromospheric Lyman-Alpha Spectro-Polarimeter
(CLASP)" that succeeded in observing for the first time the linear
polarization spectra in the hydrogen Lyman-α line (121.6 nm) and is
scheduled to be launched in 2019. In CLASP2, we will carry out full
Stokes-vector spectropolarimetric observations in the Mg ii h and k
lines near 280 nm with the spectro-polarimeter (SP), while imaging
observations in the Lyman-α line will be conducted with the slitjaw
optics (SJ). For the wavelength selection of CLASP2, the primary
mirror of the telescope uses a new dual-band pass cold mirror coating
targeting both at 121.6 nm and 280 nm. Therefore, we have to perform
again the alignment of the telescope after the installation of the
recoated primary mirror. Before unmounting the primary mirror from
the telescope structure, we measured the wave-front error (WFE) of the
telescope. The measured WFE map was consistent with what we had before
the CLASP flight, clearly indicating that the telescope alignment has
been maintained even after the flight. After the re-coated primary
mirror was installed the WFE was measured, and coma aberration was
found to be larger. Finally, the secondary mirror shim adjustments
were carried out based on the WFE measurements. In CLASP2 telescope,
we improved a fitting method of WFE map (applying 8th terms circular
Zernike polynomial fitting instead of 37th terms circular Zernike
fitting) and the improved method enables to achieve better performance
than CLASP telescope. Indeed, WFE map obtained after the final shim
adjustment indicated that the required specification (< 5.5 μm
RMS spot radius) that is more stringent than CLASP telescope was met.
---------------------------------------------------------
Title: Optical alignment of the high-precision UV spectro-polarimeter
(CLASP2)
Authors: Song, Donguk; Ishikawa, Ryohko; Kano, Ryouhei; Yoshida,
Masaki; Tsuzuki, Toshihiro; Uraguchi, Fumihiro; Shinoda, Kazuya;
Hara, Hirohisa; Okamoto, Takenori J.; Auchère, Frédéric; McKenzie,
David E.; Rachmeler, Laurel A.; Trujillo Bueno, Javier
2018SPIE10699E..2WS Altcode:
Chromospheric LAyer Spectro-Polarimeter (CLASP2) is our next sounding
rocket experiment after the success of Chromospheric Lyman-Alpha
Spectro-Polarimeter (CLASP1). CLASP2 is scheduled to launch in 2019,
and aims to achieve high precision measurements (< 0.1 %) of the
linear and circular polarizations in the Mg ii h and k lines near the
280 nm, whose line cores originate in the upper solar chromosphere. The
CLASP2 spectro-polarimeter follows very successful design concept of
the CLASP1 instrument with the minimal modification. A new grating was
fabricated with the same radius of curvature as the CLASP1 grating, but
with a different ruling density. This allows us to essentially reuse
the CLASP1 mechanical structures and layout of the optics. However,
because the observing wavelength of CLASP2 is twice longer than that
of CLASP1, a magnifier optical system was newly added in front of the
cameras to double the focal length of CLASP2 and to maintain the same
wavelength resolution as CLASP1 (0.01 nm). Meanwhile, a careful optical
alignment of the spectro-polarimeter is required to reach the 0.01 nm
wavelength resolution. Therefore, we established an efficient alignment
procedure for the CLASP2 spectro-polarimeter based on an experience
of CLASP1. Here, we explain in detail the methods for achieving the
optical alignment of the CLASP2 spectro-polarimeter and discuss our
results by comparing with the performance requirements.
---------------------------------------------------------
Title: Constraining the magnetization and geometrical complexity
of the chromosphere-corona transition region via radiative transfer
modeling of the CLASP observations
Authors: Trujillo Bueno, Javier
2018cosp...42E3433T Altcode:
On 3 September 2015 an international team of scientists from Japan,
USA and Europe carried out succesfully a challenging measurement using
a vacuum ultraviolet telescope and aspectropolarimeter called CLASP,
launched by a NASA suborbital rocket (see the talk by R. Ishikawa
et al.). For the first time, CLASP measured the linear polarization
profiles of the hydrogen Lyman-alpha and Si III 120.6 nm lines
produced by the scattering of anisotropic radiation in the enigmatic
chromosphere-corona transition region of the Sun. Here we report
about the radiative transfer investigations we have carried out for
interpreting the Stokes Q/I and U/I profiles observed by CLASP in such
ultraviolet resonance lines. We explain why the observed Lyman-alpha
polarization does not show a clear center to limb variation. We show
also that the observed Stokes profiles encode a rich information on
the magnetization and geometrical complexity of the plasma of the upper
solar chromosphere.AUTHORS: J. Trujillo Bueno, J. Stepan, T. del Pino
Alemán, L. Belluzzi, A. Asensio Ramos, R. Manso Sainz, R. Ishikawa,
R. Kano, A. Winebarger, F. Auchere, N. Narukage, K. Kobayashi, T. Bando,
Y. Katsukawa, M. Kubo, S. Ishikawa, G. Giono, H. Hara, Y. Suematsu,
T. Shimizu, T. Sakao, S. Tsuneta, K. Ichimoto, J. Cirtain, P. Champey,
B. De Pontieu, R. Casini, and M. Carlsson
---------------------------------------------------------
Title: Magneto-optical Effects in the Scattering Polarization Wings
of the Ca I 4227 Å Resonance Line
Authors: Alsina Ballester, E.; Belluzzi, L.; Trujillo Bueno, J.
2018ApJ...854..150A Altcode: 2017arXiv171100372A; 2017arXiv171100372B
The linear polarization pattern produced by scattering processes in
the Ca I 4227 Å resonance line is a valuable observable for probing
the solar atmosphere. Via the Hanle effect, the very significant Q/I
and U/I line-center signals are sensitive to the presence of magnetic
fields in the lower chromosphere with strengths between 5 and 125 G,
approximately. On the other hand, partial frequency redistribution
(PRD) produces sizable signals in the wings of the Q/I profile,
which have always been thought to be insensitive to the presence
of magnetic fields. Interestingly, novel observations of this line
revealed a surprising behavior: fully unexpected signals in the
wings of the U/I profile and spatial variability in the wings of
both Q/I and U/I. We show that the magneto-optical (MO) terms of
the Stokes-vector transfer equation produce sizable signals in the
wings of U/I and a clear sensitivity of the Q/I and U/I wings to the
presence of photospheric magnetic fields with strengths similar to
those that produce the Hanle effect in the line core. This radiative
transfer investigation on the joint action of scattering processes and
the Hanle and Zeeman effects in the Ca I 4227 Å line should facilitate
the development of more reliable techniques for exploring the magnetism
of stellar atmospheres. To this end, we can now exploit the circular
polarization produced by the Zeeman effect, the magnetic sensitivity
caused by the above-mentioned MO effects in the Q/I and U/I wings,
and the Hanle effect in the line core.
---------------------------------------------------------
Title: The Physics and Diagnostic Potential of Ultraviolet
Spectropolarimetry
Authors: Trujillo Bueno, Javier; Landi Degl'Innocenti, Egidio;
Belluzzi, Luca
2018smf..book..183T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Comparison of Solar Fine Structure Observed Simultaneously
in Lyα and Mg II h
Authors: Schmit, D.; Sukhorukov, A. V.; De Pontieu, B.; Leenaarts,
J.; Bethge, C.; Winebarger, A.; Auchère, F.; Bando, T.; Ishikawa,
R.; Kano, R.; Kobayashi, K.; Narukage, N.; Trujillo Bueno, J.
2017ApJ...847..141S Altcode: 2017arXiv170900035S
The Chromospheric Lyman Alpha Spectropolarimeter (CLASP) observed the
Sun in H I Lyα during a suborbital rocket flight on 2015 September
3. The Interface Region Imaging Telescope (IRIS) coordinated with the
CLASP observations and recorded nearly simultaneous and co-spatial
observations in the Mg II h and k lines. The Mg II h and Lyα lines
are important transitions, energetically and diagnostically, in the
chromosphere. The canonical solar atmosphere model predicts that these
lines form in close proximity to each other and so we expect that the
line profiles will exhibit similar variability. In this analysis, we
present these coordinated observations and discuss how the two profiles
compare over a region of quiet Sun at viewing angles that approach the
limb. In addition to the observations, we synthesize both line profiles
using a 3D radiation-MHD simulation. In the observations, we find that
the peak width and the peak intensities are well correlated between the
lines. For the simulation, we do not find the same relationship. We
have attempted to mitigate the instrumental differences between IRIS
and CLASP and to reproduce the instrumental factors in the synthetic
profiles. The model indicates that formation heights of the lines
differ in a somewhat regular fashion related to magnetic geometry. This
variation explains to some degree the lack of correlation, observed
and synthesized, between Mg II and Lyα. Our analysis will aid in the
definition of future observatories that aim to link dynamics in the
chromosphere and transition region.
---------------------------------------------------------
Title: The Physics and Diagnostic Potential of Ultraviolet
Spectropolarimetry
Authors: Trujillo Bueno, Javier; Landi Degl'Innocenti, Egidio;
Belluzzi, Luca
2017SSRv..210..183T Altcode: 2017SSRv..tmp...15T
The empirical investigation of the magnetic field in the outer solar
atmosphere is a very important challenge in astrophysics. To this end,
we need to identify, measure and interpret observable quantities
sensitive to the magnetism of the upper chromosphere, transition
region and corona. This paper provides an overview of the physics
and diagnostic potential of spectropolarimetry in permitted spectral
lines of the ultraviolet solar spectrum, such as the Mg ii h and k
lines around 2800 Å, the hydrogen Lyman-α line at 1216 Å, and the
Lyman-α line of He ii at 304 Å. The outer solar atmosphere is an
optically pumped vapor and the linear polarization of such spectral
lines is dominated by the atomic level polarization produced by the
absorption and scattering of anisotropic radiation. Its modification
by the action of the Hanle and Zeeman effects in the inhomogeneous
and dynamic solar atmosphere needs to be carefully understood because
it encodes the magnetic field information. The circular polarization
induced by the Zeeman effect in some ultraviolet lines (e.g., Mg ii
h & k) is also of diagnostic interest, especially for probing
the outer solar atmosphere in plages and more active regions. The few
(pioneering) observational attempts carried out so far to measure the
ultraviolet spectral line polarization produced by optically pumped
atoms in the upper chromosphere, transition region and corona are also
discussed. We emphasize that ultraviolet spectropolarimetry is a key
gateway to the outer atmosphere of the Sun and of other stars.
---------------------------------------------------------
Title: CLASP/SJ Observations of Rapid Time Variations in the Lyα
Emission in a Solar Active Region
Authors: Ishikawa, Shin-nosuke; Kubo, Masahito; Katsukawa, Yukio;
Kano, Ryouhei; Narukage, Noriyuki; Ishikawa, Ryohko; Bando, Takamasa;
Winebarger, Amy; Kobayashi, Ken; Trujillo Bueno, Javier; Auchère,
Frédéric
2017ApJ...846..127I Altcode:
The Chromospheric Lyα SpectroPolarimeter (CLASP) is a sounding
rocket experiment launched on 2015 September 3 to investigate the
solar chromosphere and transition region. The slit-jaw (SJ) optical
system captured Lyα images with a high time cadence of 0.6 s. From
the CLASP/SJ observations, many variations in the solar chromosphere
and transition region emission with a timescale of <1 minute
were discovered. In this paper, we focus on the active region within
the SJ field of view and investigate the relationship between short
(<30 s) temporal variations in the Lyα emission and the coronal
structures observed by Solar Dynamics Observatory/Atmospheric Imaging
Assembly (AIA). We compare the Lyα temporal variations at the coronal
loop footpoints observed in the AIA 211 Å (≈2 MK) and AIA 171 Å
(≈0.6 MK) channels with those in the regions with bright Lyα features
without a clear association with the coronal loop footpoints. We find
more short (<30 s) temporal variations in the Lyα intensity in the
footpoint regions. Those variations did not depend on the temperature
of the coronal loops. Therefore, the temporal variations in the Lyα
intensity at this timescale range could be related to the heating of
the coronal structures up to temperatures around the sensitivity peak
of 171 Å. No signature was found to support the scenario that these
Lyα intensity variations were related to the nanoflares. Waves or
jets from the lower layers (lower chromosphere or photosphere) are
possible causes for this phenomenon.
---------------------------------------------------------
Title: CLASP2: The Chromospheric LAyer Spectro-Polarimeter
Authors: Rachmeler, Laurel; E McKenzie, David; Ishikawa, Ryohko;
Trujillo Bueno, Javier; Auchère, Frédéric; Kobayashi, Ken;
Winebarger, Amy; Bethge, Christian; Kano, Ryouhei; Kubo, Masahito;
Song, Donguk; Narukage, Noriyuki; Ishikawa, Shin-nosuke; De Pontieu,
Bart; Carlsson, Mats; Yoshida, Masaki; Belluzzi, Luca; Stepan, Jiri;
del Pino Alemná, Tanausú; Ballester, Ernest Alsina; Asensio Ramos,
Andres
2017SPD....4811010R Altcode:
We present the instrument, science case, and timeline of the CLASP2
sounding rocket mission. The successful CLASP (Chromospheric Lyman-Alpha
Spectro-Polarimeter) sounding rocket flight in 2015 resulted in
the first-ever linear polarization measurements of solar hydrogen
Lyman-alpha line, which is sensitive to the Hanle effect and can be used
to constrain the magnetic field and geometric complexity of the upper
chromosphere. Ly-alpha is one of several upper chromospheric lines that
contain magnetic information. In the spring of 2019, we will re-fly
the modified CLASP telescope to measure the full Stokes profile of Mg
II h & k near 280 nm. This set of lines is sensitive to the upper
chromospheric magnetic field via both the Hanle and the Zeeman effects.
---------------------------------------------------------
Title: CLASP2: The Chromospheric LAyer Spectro-Polarimeter
Authors: Rachmeler, Laurel A.; McKenzie, D. E.; Ishikawa, R.;
Trujillo-Bueno, J.; Auchere, F.; Kobayashi, K.; Winebarger, A.;
Bethge, C.; Kano, R.; Kubo, M.; Song, D.; Narukage, N.; Ishikawa, S.;
De Pontieu, B.; Carlsson, M.; Yoshida, M.; Belluzzi, L.; Stepan, J.;
del Pino Alemán, T.; Alsina Ballester, E.; Asensio Ramos, A.
2017shin.confE..79R Altcode:
We present the instrument, science case, and timeline of the CLASP2
sounding rocket mission. The successful CLASP (Chromospheric Lyman-Alpha
Spectro-Polarimeter) sounding rocket flight in 2015 resulted in
the first-ever linear polarization measurements of solar hydrogen
Lyman-alpha line, which is sensitive to the Hanle effect and can be used
to constrain the magnetic field and geometric complexity of the upper
chromosphere. Ly-alpha is one of several upper chromospheric lines that
contain magnetic information. In the spring of 2019, we will re-fly
the modified CLASP telescope to measure the full Stokes profile of Mg
II h & k near 280 nm. This set of lines is sensitive to the upper
chromospheric magnetic field via both the Hanle and the Zeeman effects.
---------------------------------------------------------
Title: A Si I atomic model for NLTE spectropolarimetric diagnostics
of the 10 827 Å line
Authors: Shchukina, N. G.; Sukhorukov, A. V.; Trujillo Bueno, J.
2017A&A...603A..98S Altcode:
<BR /> Aims: The Si I 10 827 Å line is commonly used for
spectropolarimetric diagnostics of the solar atmosphere. First, we aim
at quantifying the sensitivity of the Stokes profiles of this line to
non-local thermodynamic equilibrium (NLTE) effects. Second, we aim at
facilitating NLTE diagnostics of the Si I 10 827 Å line. To this end,
we propose the use of a relatively simple silicon model atom, which
allows a fast and accurate computation of Stokes profiles. The NLTE
Stokes profiles calculated using this simple model atom are very similar
to those obtained via the use of a very comprehensive silicon model
atom. <BR /> Methods: We investigate the impact of the NLTE effects
on the Si I 10 827 Å line by means of multilevel radiative transfer
calculations in a three-dimensional (3D) model atmosphere taken from a
state-of-the-art magneto-convection simulation with small-scale dynamo
action. We calculate the emergent Stokes profiles for this line at the
solar disk center and for every vertical column of the 3D snapshot
model, neglecting the effects of horizontal radiative transfer. <BR
/> Results: We find significant departures from LTE in the Si I 10
827 Å line, not only in the intensity but also in the linearly and
circularly polarized profiles. At wavelengths around 0.1 Å, where
most of the Stokes Q, U, and V peaks of the Si I 10 827 Å line occur,
the differences between the NLTE and LTE profiles are comparable with
the Stokes amplitudes themselves. The deviations from LTE increase
with increasing Stokes Q, U, and V signals. Concerning the Stokes V
profiles, the NLTE effects correlate with the magnetic field strength
in the layers where such circular polarization signals are formed. <BR
/> Conclusions: The NLTE effects should be taken into account when
diagnosing the emergent Stokes I profiles as well as the Stokes Q, U,
and V profiles of the Si I 10 827 Å line. The sixteen-level silicon
model atom proposed here, with six radiative bound-bound transitions,
is suitable to account for the physics of formation of the Si I 10
827 Å line and for modeling and inverting its Stokes profiles without
assuming LTE.
---------------------------------------------------------
Title: Center-to-limb variation of the continuum intensity and linear
polarization of stars with transiting exoplanets
Authors: Shchukina, N. G.; Trujillo Bueno, J.; Vasilyeva, I. E.;
Frantseva, K. V.
2017KPCB...33..166S Altcode:
The limb darkening and center-to-limb variation of the continuum
polarization is calculated for a grid of one-dimensional stellar
model atmospheres and for a wavelength range between 300 and 950
nm. Model parameters match those of the transiting stars taken from
the NASA exoplanet archive. The limb darkening of the continuum
radiation for these stars is shown to decrease with the rise in
their effective temperature. For the λ = 370 nm wavelength, which
corresponds to the maximum of the Johnson-Cousins UX filter, the
limb darkening values of the planet transiting stars lie in a range
between 0.03 and 0.3. The continuum linear polarization depends
not only on the effective temperature of the star but also on its
gravity and metallicity. Its value decreases for increasing values of
these parameters. In the UX band, the maximum linear polarization of
stars with transiting planets amounts to 4%, while the minimum value
is approximately 0.3%. The continuum limb darkening and the linear
polarization decrease rapidly with wavelength. At the R band maximum
(λ = 700 nm), the linear polarization close to the limb is in fact two
orders of magnitude smaller than in the UX band. The center- to-limb
variation of the continuum intensity and the linear polarization of
the stars with transiting planets can be approximated, respectively,
by polynomials of the fourth and the sixth degree. The coefficients
of the polynomials, as well as the IDL procedures for reading them,
are available in electronic form. It is shown that there are two
classes of stars with high linear polarization at the limb. The first
one consists of cold dwarfs. Their typical representatives are HATS-6,
Kepler-45, as well as all the stars with similar parameters. The second
class of stars includes hotter giants and subgiants. Among them we have
CoRoT-28, Kepler-91, and the group of stars with effective temperatures
and gravities of approximately 5000 K and 3.5, respectively.
---------------------------------------------------------
Title: Indication of the Hanle Effect by Comparing the Scattering
Polarization Observed by CLASP in the Lyα and Si III 120.65 nm Lines
Authors: Ishikawa, R.; Trujillo Bueno, J.; Uitenbroek, H.; Kubo, M.;
Tsuneta, S.; Goto, M.; Kano, R.; Narukage, N.; Bando, T.; Katsukawa,
Y.; Ishikawa, S.; Giono, G.; Suematsu, Y.; Hara, H.; Shimizu, T.;
Sakao, T.; Winebarger, A.; Kobayashi, K.; Cirtain, J.; Champey, P.;
Auchère, F.; Štěpán, J.; Belluzzi, L.; Asensio Ramos, A.; Manso
Sainz, R.; De Pontieu, B.; Ichimoto, K.; Carlsson, M.; Casini, R.
2017ApJ...841...31I Altcode:
The Chromospheric Lyman-Alpha Spectro-Polarimeter is a sounding
rocket experiment that has provided the first successful measurement
of the linear polarization produced by scattering processes in
the hydrogen Lyα line (121.57 nm) radiation of the solar disk. In
this paper, we report that the Si III line at 120.65 nm also shows
scattering polarization and we compare the scattering polarization
signals observed in the Lyα and Si III lines in order to search for
observational signatures of the Hanle effect. We focus on four selected
bright structures and investigate how the U/I spatial variations vary
between the Lyα wing, the Lyα core, and the Si III line as a function
of the total unsigned photospheric magnetic flux estimated from Solar
Dynamics Observatory/Helioseismic and Magnetic Imager observations. In
an internetwork region, the Lyα core shows an antisymmetric spatial
variation across the selected bright structure, but it does not show
it in other more magnetized regions. In the Si III line, the spatial
variation of U/I deviates from the above-mentioned antisymmetric
shape as the total unsigned photospheric magnetic flux increases. A
plausible explanation of this difference is the operation of the Hanle
effect. We argue that diagnostic techniques based on the scattering
polarization observed simultaneously in two spectral lines with very
different sensitivities to the Hanle effect, like Lyα and Si III,
are of great potential interest for exploring the magnetism of the
upper solar chromosphere and transition region.
---------------------------------------------------------
Title: Polarization Calibration of the Chromospheric Lyman-Alpha
SpectroPolarimeter for a 0.1% Polarization Sensitivity in the VUV
Range. Part II: In-Flight Calibration
Authors: Giono, G.; Ishikawa, R.; Narukage, N.; Kano, R.; Katsukawa,
Y.; Kubo, M.; Ishikawa, S.; Bando, T.; Hara, H.; Suematsu, Y.;
Winebarger, A.; Kobayashi, K.; Auchère, F.; Trujillo Bueno, J.;
Tsuneta, S.; Shimizu, T.; Sakao, T.; Cirtain, J.; Champey, P.; Asensio
Ramos, A.; Štěpán, J.; Belluzzi, L.; Manso Sainz, R.; De Pontieu,
B.; Ichimoto, K.; Carlsson, M.; Casini, R.; Goto, M.
2017SoPh..292...57G Altcode:
The Chromospheric Lyman-Alpha SpectroPolarimeter is a sounding
rocket instrument designed to measure for the first time the linear
polarization of the hydrogen Lyman-α line (121.6 nm). The instrument
was successfully launched on 3 September 2015 and observations were
conducted at the solar disc center and close to the limb during the
five-minutes flight. In this article, the disc center observations are
used to provide an in-flight calibration of the instrument spurious
polarization. The derived in-flight spurious polarization is consistent
with the spurious polarization levels determined during the pre-flight
calibration and a statistical analysis of the polarization fluctuations
from solar origin is conducted to ensure a 0.014% precision on the
spurious polarization. The combination of the pre-flight and the
in-flight polarization calibrations provides a complete picture of
the instrument response matrix, and a proper error transfer method
is used to confirm the achieved polarization accuracy. As a result,
the unprecedented 0.1% polarization accuracy of the instrument in the
vacuum ultraviolet is ensured by the polarization calibration.
---------------------------------------------------------
Title: Discovery of Scattering Polarization in the Hydrogen Lyα
Line of the Solar Disk Radiation
Authors: Kano, R.; Trujillo Bueno, J.; Winebarger, A.; Auchère, F.;
Narukage, N.; Ishikawa, R.; Kobayashi, K.; Bando, T.; Katsukawa, Y.;
Kubo, M.; Ishikawa, S.; Giono, G.; Hara, H.; Suematsu, Y.; Shimizu,
T.; Sakao, T.; Tsuneta, S.; Ichimoto, K.; Goto, M.; Belluzzi, L.;
Štěpán, J.; Asensio Ramos, A.; Manso Sainz, R.; Champey, P.;
Cirtain, J.; De Pontieu, B.; Casini, R.; Carlsson, M.
2017ApJ...839L..10K Altcode: 2017arXiv170403228K
There is a thin transition region (TR) in the solar atmosphere where
the temperature rises from 10,000 K in the chromosphere to millions
of degrees in the corona. Little is known about the mechanisms that
dominate this enigmatic region other than the magnetic field plays a
key role. The magnetism of the TR can only be detected by polarimetric
measurements of a few ultraviolet (UV) spectral lines, the Lyα line
of neutral hydrogen at 121.6 nm (the strongest line of the solar UV
spectrum) being of particular interest given its sensitivity to the
Hanle effect (the magnetic-field-induced modification of the scattering
line polarization). We report the discovery of linear polarization
produced by scattering processes in the Lyα line, obtained with
the Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) rocket
experiment. The Stokes profiles observed by CLASP in quiet regions of
the solar disk show that the Q/I and U/I linear polarization signals are
of the order of 0.1% in the line core and up to a few percent in the
nearby wings, and that both have conspicuous spatial variations with
scales of ∼10 arcsec. These observations help constrain theoretical
models of the chromosphere-corona TR and extrapolations of the
magnetic field from photospheric magnetograms. In fact, the observed
spatial variation from disk to limb of polarization at the line core
and wings already challenge the predictions from three-dimensional
magnetohydrodynamical models of the upper solar chromosphere.
---------------------------------------------------------
Title: The Physical Origin and Magnetic Sensitivity of the Scattering
Polarization Observed in the O I IR Triplet at 777 nm
Authors: del Pino Alemán, T.; Trujillo Bueno, J.
2017ApJ...838..164D Altcode:
The linearly polarized solar limb spectrum caused by the absorption
and scattering of anisotropic radiation has a very rich diagnostic
potential, given its sensitivity to the thermal, dynamic, and magnetic
structure of the solar atmosphere. A crucial first step toward its
scientific exploitation is understanding the physical origin of the
observed spectral line polarization and its magnetic sensitivity via
the Hanle and Zeeman effects. Here, we study the linear polarization
signals observed in the IR triplet of O I at 777 nm, describing in
detail the multilevel radiative transfer calculations that allowed
us to decipher their physical origin. We investigate the sensitivity
of the calculated scattering polarization signals to various modeling
parameters, finding that the observed fractional linear polarization
pattern originates mainly in the solar chromosphere, although the
intensity profiles of the O I IR triplet come mainly from the lower
photosphere. We find that the three lines are sensitive, via the
Hanle effect, to magnetic fields with strengths between 0.01 and 30
G, in a extended region of the solar atmosphere. We show this through
calculations of the response function to magnetic field perturbations
in a semi-empirical model of the quiet Sun atmosphere. The dominant
response of the linear polarization signals occurs at heights ∼
1000 km above the visible model’s surface, which demonstrates that
the scattering linear polarization signals of the oxygen IR triplet
encode information on the magnetism of the solar chromosphere.
---------------------------------------------------------
Title: The Transfer of Resonance Line Polarization with Partial
Frequency Redistribution in the General Hanle-Zeeman Regime
Authors: Alsina Ballester, E.; Belluzzi, L.; Trujillo Bueno, J.
2017ApJ...836....6A Altcode: 2016arXiv160905723B; 2016arXiv160905723A; 2017ApJ...836....6B
The spectral line polarization encodes a wealth of information about the
thermal and magnetic properties of the solar atmosphere. Modeling the
Stokes profiles of strong resonance lines is, however, a complex problem
both from a theoretical and computational point of view, especially when
partial frequency redistribution (PRD) effects need to be taken into
account. In this work, we consider a two-level atom in the presence
of magnetic fields of arbitrary intensity (Hanle-Zeeman regime) and
orientation, both deterministic and micro-structured. Working within the
framework of a rigorous PRD theoretical approach, we have developed
a numerical code that solves the full non-LTE radiative transfer
problem for polarized radiation, in one-dimensional models of the
solar atmosphere, accounting for the combined action of the Hanle and
Zeeman effects, as well as for PRD phenomena. After briefly discussing
the relevant equations, we describe the iterative method of solution
of the problem and the numerical tools that we have developed and
implemented. We finally present some illustrative applications to two
resonance lines that form at different heights in the solar atmosphere,
and provide a detailed physical interpretation of the calculated Stokes
profiles. We find that magneto-optical effects have a strong impact on
the linear polarization signals that PRD effects produce in the wings of
strong resonance lines. We also show that the weak-field approximation
has to be used with caution when PRD effects are considered.
---------------------------------------------------------
Title: A novel radiative transfer investigation of the magnetic
micro-activity of the quiet Sun via the Hanle effect in the Sr I
460.7 nm line
Authors: Trujillo Bueno, Javier
2017psio.confE..29T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Polarization Calibration of the Chromospheric Lyman-Alpha
SpectroPolarimeter for a 0.1 % Polarization Sensitivity in the VUV
Range. Part I: Pre-flight Calibration
Authors: Giono, G.; Ishikawa, R.; Narukage, N.; Kano, R.; Katsukawa,
Y.; Kubo, M.; Ishikawa, S.; Bando, T.; Hara, H.; Suematsu, Y.;
Winebarger, A.; Kobayashi, K.; Auchère, F.; Trujillo Bueno, J.
2016SoPh..291.3831G Altcode: 2016SoPh..tmp..177G
The Chromospheric Lyman-Alpha SpectroPolarimeter (CLASP) is a sounding
rocket experiment designed to measure for the first time the linear
polarization of the hydrogen Lyman-α line (121.6 nm) and requires
a 0.1 % polarization sensitivity, which is unprecedented for a
spectropolarimeter in the vacuum UV (VUV) spectral range.
---------------------------------------------------------
Title: Discovery of Ubiquitous Fast-Propagating Intensity Disturbances
by the Chromospheric Lyman Alpha Spectropolarimeter (CLASP)
Authors: Kubo, M.; Katsukawa, Y.; Suematsu, Y.; Kano, R.; Bando,
T.; Narukage, N.; Ishikawa, R.; Hara, H.; Giono, G.; Tsuneta, S.;
Ishikawa, S.; Shimizu, T.; Sakao, T.; Winebarger, A.; Kobayashi, K.;
Cirtain, J.; Champey, P.; Auchère, F.; Trujillo Bueno, J.; Asensio
Ramos, A.; Štěpán, J.; Belluzzi, L.; Manso Sainz, R.; De Pontieu,
B.; Ichimoto, K.; Carlsson, M.; Casini, R.; Goto, M.
2016ApJ...832..141K Altcode:
High-cadence observations by the slit-jaw (SJ) optics system of the
sounding rocket experiment known as the Chromospheric Lyman Alpha
Spectropolarimeter (CLASP) reveal ubiquitous intensity disturbances
that recurrently propagate in either the chromosphere or the transition
region or both at a speed much higher than the speed of sound. The
CLASP/SJ instrument provides a time series of two-dimensional images
taken with broadband filters centered on the Lyα line at a 0.6 s
cadence. The multiple fast-propagating intensity disturbances appear in
the quiet Sun and in an active region, and they are clearly detected in
at least 20 areas in a field of view of 527″ × 527″ during the 5
minute observing time. The apparent speeds of the intensity disturbances
range from 150 to 350 km s<SUP>-1</SUP>, and they are comparable
to the local Alfvén speed in the transition region. The intensity
disturbances tend to propagate along bright elongated structures away
from areas with strong photospheric magnetic fields. This suggests
that the observed fast-propagating intensity disturbances are related
to the magnetic canopy structures. The maximum distance traveled by
the intensity disturbances is about 10″, and the widths are a few
arcseconds, which are almost determined by a pixel size of 1.″03. The
timescale of each intensity pulse is shorter than 30 s. One possible
explanation for the fast-propagating intensity disturbances observed
by CLASP is magnetohydrodynamic fast-mode waves.
---------------------------------------------------------
Title: The Magnetic Sensitivity of the Mg II k Line to the Joint
Action of Hanle, Zeeman, and Magneto-optical Effects
Authors: Alsina Ballester, E.; Belluzzi, L.; Trujillo Bueno, J.
2016ApJ...831L..15A Altcode: 2016arXiv161000649A
We highlight the main results of a radiative transfer investigation on
the magnetic sensitivity of the solar Mg II k resonance line at 2795.5
Å, accounting for the joint action of the Hanle and Zeeman effects
as well as partial frequency redistribution phenomena. We confirm
that at the line center, the linear polarization signals produced by
scattering processes are measurable, and that they are sensitive, via
the Hanle effect, to magnetic fields with strengths between 5 and 50 G,
approximately. We also show that the Zeeman effect produces conspicuous
circular polarization signals, especially for longitudinal fields
stronger than 50 G, which can be used to estimate the magnetization of
the solar chromosphere via the familiar magnetograph formula. The most
novel result is that magneto-optical effects produce, in the wings of
the line, a decrease of the Q/I scattering polarization pattern and
the appearance of U/I signals (I.e., a rotation of the plane of linear
polarization). This sensitivity of the Q/I and U/I wing signals to
both weak (∼5 G) and stronger magnetic fields expands the scientific
interest of the Mg II k line for probing the chromosphere in quiet
and active regions of the Sun.
---------------------------------------------------------
Title: Optical alignment of the Chromospheric Lyman-Alpha
Spectro-Polarimeter using sophisticated methods to minimize activities
under vacuum
Authors: Giono, G.; Katsukawa, Y.; Ishikawa, R.; Narukage, N.;
Kano, R.; Kubo, M.; Ishikawa, S.; Bando, T.; Hara, H.; Suematsu, Y.;
Winebarger, A.; Kobayashi, K.; Auchère, F.; Trujillo Bueno, J.
2016SPIE.9905E..3DG Altcode:
The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) is a
sounding-rocket instrument developed at the National Astronomical
Observatory of Japan (NAOJ) as a part of an international
collaboration. The instrument main scientific goal is to achieve
polarization measurement of the Lyman-α line at 121.56 nm emitted from
the solar upper-chromosphere and transition region with an unprecedented
0.1% accuracy. The optics are composed of a Cassegrain telescope
coated with a "cold mirror" coating optimized for UV reflection and
a dual-channel spectrograph allowing for simultaneous observation of
the two orthogonal states of polarization. Although the polarization
sensitivity is the most important aspect of the instrument, the spatial
and spectral resolutions of the instrument are also crucial to observe
the chromospheric features and resolve the Ly-α profiles. A precise
alignment of the optics is required to ensure the resolutions, but
experiments under vacuum conditions are needed since Ly-α is absorbed
by air, making the alignment experiments difficult. To bypass this
issue, we developed methods to align the telescope and the spectrograph
separately in visible light. We explain these methods and present
the results for the optical alignment of the CLASP telescope and
spectrograph. We then discuss the combined performances of both parts
to derive the expected resolutions of the instrument, and compare them
with the flight observations performed on September 3<SUP>rd</SUP> 2015.
---------------------------------------------------------
Title: Chromospheric LAyer SpectroPolarimeter (CLASP2)
Authors: Narukage, Noriyuki; McKenzie, David E.; Ishikawa, Ryoko;
Trujillo-Bueno, Javier; De Pontieu, Bart; Kubo, Masahito; Ishikawa,
Shin-nosuke; Kano, Ryouhei; Suematsu, Yoshinori; Yoshida, Masaki;
Rachmeler, Laurel A.; Kobayashi, Ken; Cirtain, Jonathan W.; Winebarger,
Amy R.; Asensio Ramos, Andres; del Pino Aleman, Tanausu; Štępán,
Jiri; Belluzzi, Luca; Larruquert, Juan Ignacio; Auchère, Frédéric;
Leenaarts, Jorrit; Carlsson, Mattias J. L.
2016SPIE.9905E..08N Altcode:
The sounding rocket Chromospheric Lyman-Alpha SpectroPolarimeter
(CLASP) was launched on September 3rd, 2015, and successfully detected
(with a polarization accuracy of 0.1 %) the linear polarization signals
(Stokes Q and U) that scattering processes were predicted to produce
in the hydrogen Lyman-alpha line (Lyα 121.567 nm). Via the Hanle
effect, this unique data set may provide novel information about the
magnetic structure and energetics in the upper solar chromosphere. The
CLASP instrument was safely recovered without any damage and we have
recently proposed to dedicate its second flight to observe the four
Stokes profiles in the spectral region of the Mg II h and k lines
around 280 nm; in these lines the polarization signals result from
scattering processes and the Hanle and Zeeman effects. Here we describe
the modifications needed to develop this new instrument called the
"Chromospheric LAyer SpectroPolarimeter" (CLASP2).
---------------------------------------------------------
Title: The Hanle and Zeeman Polarization Signals of the Solar Ca II
8542 Å Line
Authors: Štěpán, Jiří; Trujillo Bueno, Javier
2016ApJ...826L..10S Altcode: 2016arXiv160607741S
We highlight the main results of a three-dimensional (3D) multilevel
radiative transfer investigation about the solar disk-center
polarization of the Ca II 8542 Å line. First, through the use
of a 3D model of the solar atmosphere, we investigate the linear
polarization that occurs due to the atomic level polarization produced
by the absorption and scattering of anisotropic radiation, taking
into account the symmetry-breaking effects caused by its thermal,
dynamic, and magnetic structure. Second, we study the contribution of
the Zeeman effect to the linear and circular polarization. Finally,
we show examples of the Stokes profiles produced by the joint action
of the atomic level polarization and the Hanle and Zeeman effects. We
find that the Zeeman effect tends to dominate the linear polarization
signals only in the localized patches of opposite magnetic polarity,
where the magnetic field is relatively strong and slightly inclined;
outside such very localized patches, the linear polarization is
often dominated by the contribution of atomic level polarization. We
demonstrate that a correct modeling of this last contribution requires
taking into account the symmetry-breaking effects caused by the
thermal, dynamic, and magnetic structure of the solar atmosphere,
and that in the 3D model used the Hanle effect in forward-scattering
geometry (disk-center observation) mainly reduces the polarization
corresponding to the zero-field case. We emphasize that, in general,
a reliable modeling of the linear polarization in the Ca II 8542 Å
line requires taking into account the joint action of atomic level
polarization and the Hanle and Zeeman effects.
---------------------------------------------------------
Title: Spectro-polarimetric observation in UV with CLASP to probe
the chromosphere and transition region
Authors: Kano, Ryouhei; Ishikawa, Ryohko; Winebarger, Amy R.; Auchère,
Frédéric; Trujillo Bueno, Javier; Narukage, Noriyuki; Kobayashi,
Ken; Bando, Takamasa; Katsukawa, Yukio; Kubo, Masahito; Ishikawa,
Shin-Nosuke; Giono, Gabriel; Hara, Hirohisa; Suematsu, Yoshinori;
Shimizu, Toshifumi; Sakao, Taro; Tsuneta, Saku; Ichimoto, Kiyoshi;
Goto, Motoshi; Cirtain, Jonathan W.; De Pontieu, Bart; Casini, Roberto;
Manso Sainz, Rafael; Asensio Ramos, Andres; Stepan, Jiri; Belluzzi,
Luca; Carlsson, Mats
2016SPD....4710107K Altcode:
The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) is a NASA
sounding-rocket experiment that was performed in White Sands in
the US on September 3, 2015. During its 5-minute ballistic flight,
CLASP successfully made the first spectro-polarimetric observation in
the Lyman-alpha line (121.57 nm) originating in the chromosphere and
transition region. Since the Lyman-alpha polarization is sensitive
to magnetic field of 10-100 G by the Hanle effect, we aim to infer
the magnetic field information in such upper solar atmosphere with
this experiment.The obtained CLASP data showed that the Lyman-alpha
scattering polarization is about a few percent in the wings and
the order of 0.1% in the core near the solar limb, as it had been
theoretically predicted, and that both polarization signals have a
conspicuous spatio-temporal variability. CLASP also observed another
upper-chromospheric line, Si III (120.65 nm), whose critical field
strength for the Hanle effect is 290 G, and showed a measurable
scattering polarization of a few % in this line. The polarization
properties of the Si III line could facilitate the interpretation of
the scattering polarization observed in the Lyman-alpha line.In this
presentation, we would like to show how the upper chromosphere and
transition region are seen in the polarization of these UV lines and
discuss the possible source of these complicated polarization signals.
---------------------------------------------------------
Title: Impact of surface dynamo magnetic fields on the solar abundance
of the CNO elements
Authors: Shchukina, N.; Sukhorukov, A.; Trujillo Bueno, J.
2016A&A...586A.145S Altcode:
Most studies of the solar metallicity, based on abundance determinations
of the CNO elements, ignore the fact that the quiet solar photosphere
is significantly magnetized by a small-scale magnetic field with a
mean field strength of ~100 G. Here we quantify how this significant
magnetization affects determinations of the abundances of these chemical
elements. To this end, we used two three-dimensional models of the solar
photosphere taken from a magneto-convection simulation with small-scale
dynamo action, one virtually unmagnetized, and the other characterized
by a mean field strength of 160 G in the low photosphere. We performed
local thermodynamic equilibrium spectral synthesis for a large set of C
I, N I, and O I lines to derive abundance corrections. We included the
magnetic broadening of the lines (direct effect) and the magnetically
induced changes of the photospheric temperature stratification (indirect
effect). We find that these small-scale dynamo magnetic fields only
negligibly affect the determination of the solar abundances of carbon,
nitrogen, and oxygen.
---------------------------------------------------------
Title: Radiative Transfer Modeling of the Enigmatic Scattering
Polarization in the Solar Na I D1 Line
Authors: Belluzzi, Luca; Trujillo Bueno, Javier; Landi Degl'Innocenti,
Egidio
2015ApJ...814..116B Altcode: 2015arXiv151105801B
The modeling of the peculiar scattering polarization signals
observed in some diagnostically important solar resonance lines
requires the consideration of the detailed spectral structure of the
incident radiation field as well as the possibility of ground level
polarization, along with the atom's hyperfine structure and quantum
interference between hyperfine F-levels pertaining either to the same
fine structure J-level, or to different J-levels of the same term. Here
we present a theoretical and numerical approach suitable for solving
this complex non-LTE radiative transfer problem. This approach is based
on the density-matrix metalevel theory (where each level is viewed as
a continuous distribution of sublevels) and on accurate formal solvers
of the transfer equations and efficient iterative methods. We show an
application to the D-lines of Na i, with emphasis on the enigmatic
D<SUB>1</SUB> line, pointing out the observable signatures of the
various physical mechanisms considered. We demonstrate that the linear
polarization observed in the core of the D<SUB>1</SUB> line may be
explained by the effect that one gets when the detailed spectral
structure of the anisotropic radiation responsible for the optical
pumping is taken into account. This physical ingredient is capable of
introducing significant scattering polarization in the core of the Na
i D<SUB>1</SUB> line without the need for ground-level polarization.
---------------------------------------------------------
Title: Atomic Scattering Polarization. Observations, Modeling,
Predictions
Authors: Trujillo Bueno, J.; Del Pino Alemán, T.; Belluzzi, L.
2015IAUS..305..127T Altcode: 2015IAUS..305..127B
This paper highlights very recent advances concerning the identification
of new mechanisms that introduce polarization in spectral lines,
which turn out to be key for understanding some of the most enigmatic
scattering polarization signals of the solar visible spectrum. We also
show a radiative transfer prediction on the scattering polarization
pattern across the Mg ii h & k lines, whose radiation can only be
observed from space.
---------------------------------------------------------
Title: Isotropic Inelastic Collisions in a Multiterm Atom with
Hyperfine Structure
Authors: Belluzzi, Luca; Landi Degl'Innocenti, Egidio; Trujillo
Bueno, Javier
2015ApJ...812...73B Altcode:
A correct modeling of the scattering polarization profiles observed
in some spectral lines of diagnostic interest, the sodium doublet
being one of the most important examples, requires taking hyperfine
structure (HFS) and quantum interference between different J-levels
into account. An atomic model suitable for taking these physical
ingredients into account is the so-called multiterm atom with HFS. In
this work, we introduce and study the transfer and relaxation rates
due to isotropic inelastic collisions with electrons, which enter the
statistical equilibrium equations (SEE) for the atomic density matrix
of this atomic model. Under the hypothesis that the electron-atom
interaction is described by a dipolar operator, we provide useful
relations between the rates describing the transfer and relaxation of
quantum interference between different levels (whose numerical values
are in most cases unknown) and the usual rates for the atomic level
populations, for which experimental data and/or approximate theoretical
expressions are generally available. For the particular case of a
two-term atom with HFS, we present an analytical solution of the SEE
for the spherical statistical tensors of the upper term, including both
radiative and collisional processes, and we derive the expression of
the emission coefficient in the four Stokes parameters. Finally, an
illustrative application to the Na i D<SUB>1</SUB> and D<SUB>2</SUB>
lines is presented.
---------------------------------------------------------
Title: The impact of surface dynamo magnetic fields on the chemical
abundance determination
Authors: Shchukina, Nataliya G.; Sukhorukov, Andrii V.; Trujillo
Bueno, Javier
2015IAUS..305..368S Altcode:
The solar abundances of Fe and of the CNO elements play an important
role in addressing a number of important issues such as the formation,
structure, and evolution of the Sun and the solar system, the origin of
the chemical elements, and the evolution of stars and galaxies. Despite
the large number of papers published on this issue, debates about the
solar abundances of these elements continue. The aim of the present
investigation is to quantify the impact of photospheric magnetic fields
on the determination of the solar chemical abundances. To this end,
we used two 3D snapshot models of the quiet solar photosphere with a
different magnetization taken from recent magneto-convection simulations
with small-scale dynamo action. Using such 3D models we have carried
out spectral synthesis for a large set of Fei, Ci, Ni, and Oi lines,
in order to derive abundance corrections caused by the magnetic, Zeeman
broadening of the intensity profiles and the magnetically induced
changes of the photospheric temperature structure. We find that if
the magnetism of the quiet solar photosphere is mainly produced by
a small-scale dynamo, then its impact on the determination of the
abundances of iron, carbon, nitrogen and oxygen is negligible.
---------------------------------------------------------
Title: Formation of polarized spectral lines in atmospheres with
horizontal inhomogeneities
Authors: Tichý, A.; Štěpán, J.; Trujillo Bueno, J.; Kubát, J.
2015IAUS..305..401T Altcode:
We study the problem of the generation and transfer of spectral line
intensity and polarization in models of stellar atmospheres with
horizontal plasma inhomogeneities. We solve the non-LTE radiative
transfer problem in full 3D geometry taking into account resonant
scattering polarization and its modification by magnetic fields
via the Hanle effect. We show that horizontal fluctuations of
the thermodynamical conditions of stellar atmospheres can have a
significant impact on the linear polarization of the emergent spectral
line radiation and its center-to-limb variation.
---------------------------------------------------------
Title: CLASP: A UV Spectropolarimeter on a Sounding Rocket for
Probing theChromosphere-Corona Transition Regio
Authors: Ishikawa, Ryohko; Kano, Ryouhei; Winebarger, Amy; Auchere,
Frederic; Trujillo Bueno, Javier; Bando, Takamasa; Narukage,
Noriyuki; Kobayashi, Ken; Katsukawa, Yukio; Kubo, Masahito; Ishikawa,
Shin-nosuke; Giono, Gabriel; Tsuneta, Saku; Hara, Hirohisa; Suematsu,
Yoshinori; Shimizu, Toshifumi; Sakao, Taro; Ichimoto, Kiyoshi;
Cirtain, Jonathan; De Pontieu, Bart; Casini, Roberto; Manso Sainz,
Rafael; Asensio Ramos, Andres; Stepan, Jiri; Belluzzi, Luca
2015IAUGA..2254536I Altcode:
The wish to understand the energetic phenomena of the outer solar
atmosphere makes it increasingly important to achieve quantitative
information on the magnetic field in the chromosphere-corona
transition region. To this end, we need to measure and model the
linear polarization produced by scattering processes and the Hanle
effect in strong UV resonance lines, such as the hydrogen Lyman-alpha
line. A team consisting of Japan, USA, Spain, France, and Norway has
been developing a sounding rocket experiment called the Chromospheric
Lyman-alpha Spectro-Polarimeter (CLASP). The aim is to detect the
scattering polarization produced by anisotropic radiation pumping in
the hydrogen Lyman-alpha line (121.6 nm), and via the Hanle effect to
try to constrain the magnetic field vector in the upper chromosphere
and transition region. In this talk, we will present an overview
of our CLASP mission, its scientific objectives, ground tests made,
and the latest information on the launch planned for the Summer of 2015.
---------------------------------------------------------
Title: The impact of surface dynamo magnetic fields on the solar
iron abundance
Authors: Shchukina, N.; Trujillo Bueno, J.
2015A&A...579A.112S Altcode:
Most chemical abundance determinations ignore that the solar photosphere
is significantly magnetized by the ubiquitous presence of a small-scale
magnetic field. A recent investigation has suggested that there
should be a significant impact on the derived iron abundance, owing
to the magnetically induced changes on the photospheric temperature
and density structure (indirect effect). The three-dimensional (3D)
photospheric models used in that investigation have non-zero net
magnetic flux values and stem from magneto-convection simulations
without small-scale dynamo action. Here we address the same problem
by instead using 3D models of the quiet solar photosphere that result
from a state-of-the-art magneto-convection simulation with small-scale
dynamo action, where the net magnetic flux is zero. One of these 3D
models has negligible magnetization, while the other is characterized
by a mean field strength of 160 Gauss in the low photosphere. With
such 3D models we carried out spectral synthesis for a large set of Fe
i lines to derive abundance corrections, taking the above-mentioned
indirect effect and the Zeeman broadening of the intensity profiles
(direct effect) into account. We conclude that if the magnetism of the
quiet solar photosphere is mainly produced by a small-scale dynamo,
then its impact on the determination of the solar iron abundance
is negligible. <P />Table 1 is available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201425569/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: Chromospheric Polarization in the Photospheric Solar Oxygen
Infrared Triplet
Authors: Del Pino Alemán, Tanausú; Trujillo Bueno, Javier
2015ApJ...808L..13D Altcode: 2015arXiv150703356D
We present multilevel radiative transfer modeling of the scattering
polarization observed in the solar O i infrared triplet around 777
nm. We demonstrate that the scattering polarization pattern observed
on the solar disk forms in the chromosphere, far above the photospheric
region where the bulk of the emergent intensity profiles originate. We
investigate the sensitivity of the polarization pattern to the thermal
structure of the solar atmosphere and to the presence of weak magnetic
fields (10<SUP>-2</SUP>-100 G) through the Hanle effect, showing that
the scattering polarization signals of the oxygen infrared triplet
encode information on the magnetism of the solar chromosphere.
---------------------------------------------------------
Title: An open-source, massively parallel code for non-LTE synthesis
and inversion of spectral lines and Zeeman-induced Stokes profiles
Authors: Socas-Navarro, H.; de la Cruz Rodríguez, J.; Asensio Ramos,
A.; Trujillo Bueno, J.; Ruiz Cobo, B.
2015A&A...577A...7S Altcode: 2014arXiv1408.6101S
With the advent of a new generation of solar telescopes and
instrumentation, interpreting chromospheric observations (in
particular, spectropolarimetry) requires new, suitable diagnostic
tools. This paper describes a new code, NICOLE, that has been
designed for Stokes non-LTE radiative transfer, for synthesis and
inversion of spectral lines and Zeeman-induced polarization profiles,
spanning a wide range of atmospheric heights from the photosphere
to the chromosphere. The code features a number of unique features
and capabilities and has been built from scratch with a powerful
parallelization scheme that makes it suitable for application on
massive datasets using large supercomputers. The source code is
written entirely in Fortran 90/2003 and complies strictly with the
ANSI standards to ensure maximum compatibility and portability. It
is being publicly released, with the idea of facilitating future
branching by other groups to augment its capabilities. <P />The
source code is currently hosted at the following repository: <A
href="http://github.com/hsocasnavarro/NICOLE">https://github.com/hsocasnavarro/NICOLE</A>
---------------------------------------------------------
Title: Highlights of Spanish Astrophysics VIII
Authors: Cenarro, A. J.; Figueras, F.; Hernández-Monteagudo, C.;
Trujillo Bueno, J.; Valdivielso, L.
2015hsa8.conf.....C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Height Variation of the Vector Magnetic Field in Solar Spicules
Authors: Orozco Suárez, D.; Asensio Ramos, A.; Trujillo Bueno, J.
2015ApJ...803L..18O Altcode: 2015arXiv150404637O
Proving the magnetic configuration of solar spicules has hitherto been
difficult due to the lack of spatial resolution and image stability
during off-limb ground-based observations. We report spectropolarimetric
observations of spicules taken in the He i 1083 nm spectral region
with the Tenerife Infrared Polarimeter II at the German Vacuum Tower
Telescope of the Observatorio del Teide (Tenerife, Canary Islands,
Spain). The data provide the variation with geometrical height of
the Stokes I, Q, U, and V profiles, whose encoded information allows
the determination of the magnetic field vector by means of the HAZEL
inversion code. The inferred results show that the average magnetic
field strength at the base of solar spicules is about 80 gauss, and
then it decreases rapidly with height to about 30 gauss at a height of
3000 km above the visible solar surface. Moreover, the magnetic field
vector is close to vertical at the base of the chromosphere and has
mid-inclinations (about 50°) above 2 Mm height.
---------------------------------------------------------
Title: Three-dimensional Radiative Transfer Simulations of
the Scattering Polarization of the Hydrogen Lyα Line in a
Magnetohydrodynamic Model of the Chromosphere-Corona Transition Region
Authors: Štěpán, J.; Trujillo Bueno, J.; Leenaarts, J.; Carlsson, M.
2015ApJ...803...65S Altcode: 2015arXiv150106382S
Probing the magnetism of the upper solar chromosphere requires measuring
and modeling the scattering polarization produced by anisotropic
radiation pumping in UV spectral lines. Here we apply PORTA (a novel
radiative transfer code) to investigate the hydrogen Lyα line in
a three-dimensional model of the solar atmosphere resulting from a
state of the art magnetohydrodynamic (MHD) simulation. At full spatial
resolution the linear polarization signals are very significant all
over the solar disk, with a large fraction of the field of view (FOV)
showing line-center amplitudes well above the 1% level. Via the Hanle
effect the line-center polarization signals are sensitive to the
magnetic field of the model's transition region, even when its mean
field strength is only 15 G. The breaking of the axial symmetry of the
radiation field produces significant forward-scattering polarization
in Lyα, without the need of an inclined magnetic field. Interestingly,
the Hanle effect tends to decrease such forward-scattering polarization
signals in most of the points of the FOV. When the spatial resolution is
degraded, the line-center polarization of Lyα drops below the 1% level,
reaching values similar to those previously found in one-dimensional
(1D) semi-empirical models (i.e., up to about 0.5 %). The center to
limb variation (CLV) of the spatially averaged polarization signals
is qualitatively similar to that found in 1D models, with the largest
line-center amplitudes at μ =cos θ ≈ 0.4 (θ being the heliocentric
angle). These results are important, both for designing the needed
space-based instrumentation and for a reliable interpretation of future
observations of the Lyα polarization.
---------------------------------------------------------
Title: Non Coherent Continuum Scattering as a Polarization Mechanism
of the Enigmatic Ba <font size=2>II D<SUB>1</SUB> Line
Authors: del Pino Alemán, T.; Trujillo Bueno, J.; Uitenbroek, H.
2014ASPC..489..107D Altcode:
Line scattering polarization can be strongly affected by Rayleigh
scattering by neutral hydrogen and Thomson scattering by free
electrons. The assumption that continuum polarization can be modeled
as coherent scattering, an excellent approximation far from the
spectral line, yields a continuum depolarization when applied to an
intrinsically unpolarizable spectral line. However, the radiation field
is not always constant over the spectral line and continuum scattering
has to be treated non-coherently. A recent investigation showed that the
redistribution of the spectral line radiation due to the non coherence
of the continuum scattering can significantly modify the shape of
the emergent fractional linear polarization profiles, even yielding
emission Q/I features in intrinsically unpolarizable lines. Here we
show an application to the enigmatic D<SUB>1</SUB> line of Ba <font
size=2>II at 4934 Å, neglecting the hyperfine structure of the 18%
of the barium isotopes whose nuclear spin is non-zero. We show that with
this assumption Q/I signals above the continuum polarization level can
be produced in solar atmospheric models representative of polar faculae.
---------------------------------------------------------
Title: Polarized Radiation Observables for Probing the Magnetism of
the Outer Solar Atmosphere
Authors: Trujillo Bueno, J.
2014ASPC..489..137T Altcode:
The basic idea of optical pumping, for which Alfred Kastler received
the 1966 Nobel Prize in Physics, is that the absorption and scattering
of anisotropic radiation can produce population imbalances and quantum
coherence among the magnetic substates of atomic levels. The degree
of this radiatively-induced atomic level polarization, which is very
sensitive to the presence of magnetic fields, can be determined by
observing the polarization of the scattered or transmitted spectral
line radiation. The most important point for solar physics is that
the outer solar atmosphere is an optically pumped vapor and that the
polarization of the emergent spectral line radiation can be exploited
to obtain quantitative information on the strength and/or geometry
of magnetic fields within the chromosphere, transition region, and
corona. Here we review some recent investigations of the polarization
produced by optical pumping in selected IR, FUV, and EUV spectral lines,
showing that their magnetic sensitivity is suitable for probing the
magnetism of the outer solar atmosphere.
---------------------------------------------------------
Title: A Sounding Rocket Experiment for the Chromospheric Lyman-Alpha
Spectro-Polarimeter (CLASP)
Authors: Kubo, M.; Kano, R.; Kobayashi, K.; Bando, T.; Narukage, N.;
Ishikawa, R.; Tsuneta, S.; Katsukawa, Y.; Ishikawa, S.; Suematsu, Y.;
Hara, H.; Shimizu, T.; Sakao, T.; Ichimoto, K.; Goto, M.; Holloway,
T.; Winebarger, A.; Cirtain, J.; De Pontieu, B.; Casini, R.; Auchère,
F.; Trujillo Bueno, J.; Manso Sainz, R.; Belluzzi, L.; Asensio Ramos,
A.; Štěpán, J.; Carlsson, M.
2014ASPC..489..307K Altcode:
A sounding-rocket experiment called the Chromospheric Lyman-Alpha
Spectro-Polarimeter (CLASP) is presently under development to measure
the linear polarization profiles in the hydrogen Lyman-alpha (Lyα)
line at 121.567 nm. CLASP is a vacuum-UV (VUV) spectropolarimeter to aim
for first detection of the linear polarizations caused by scattering
processes and the Hanle effect in the Lyα line with high accuracy
(0.1%). This is a fist step for exploration of magnetic fields in
the upper chromosphere and transition region of the Sun. Accurate
measurements of the linear polarization signals caused by scattering
processes and the Hanle effect in strong UV lines like Lyα are
essential to explore with future solar telescopes the strength
and structures of the magnetic field in the upper chromosphere and
transition region of the Sun. The CLASP proposal has been accepted by
NASA in 2012, and the flight is planned in 2015.
---------------------------------------------------------
Title: The magnetic field configuration of a solar prominence inferred
from spectropolarimetric observations in the He i 10 830 Å triplet
Authors: Orozco Suárez, D.; Asensio Ramos, A.; Trujillo Bueno, J.
2014A&A...566A..46O Altcode: 2014arXiv1403.7976O
Context. Determining the magnetic field vector in quiescent solar
prominences is possible by interpreting the Hanle and Zeeman effects
in spectral lines. However, observational measurements are scarce and
lack high spatial resolution. <BR /> Aims: We determine the magnetic
field vector configuration along a quiescent solar prominence by
interpreting spectropolarimetric measurements in the He i 1083.0 nm
triplet obtained with the Tenerife Infrared Polarimeter installed at
the German Vacuum Tower Telescope of the Observatorio del Teide. <BR
/> Methods: The He i 1083.0 nm triplet Stokes profiles were analyzed
with an inversion code that takes the physics responsible for the
polarization signals in this triplet into account. The results are put
into a solar context with the help of extreme ultraviolet observations
taken with the Solar Dynamic Observatory and the Solar Terrestrial
Relations Observatory satellites. <BR /> Results: For the most probable
magnetic field vector configuration, the analysis depicts a mean field
strength of 7 gauss. We do not find local variations in the field
strength except that the field is, on average, lower in the prominence
body than in the prominence feet, where the field strength reaches ~25
gauss. The averaged magnetic field inclination with respect to the local
vertical is ~77°. The acute angle of the magnetic field vector with the
prominence main axis is 24° for the sinistral chirality case and 58°
for the dextral chirality. These inferences are in rough agreement with
previous results obtained from the analysis of data acquired with lower
spatial resolutions. <P />A movie is available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201322903/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: On the Inversion of the Scattering Polarization and the Hanle
Effect Signals in the Hydrogen Lyα Line
Authors: Ishikawa, R.; Asensio Ramos, A.; Belluzzi, L.; Manso Sainz,
R.; Štěpán, J.; Trujillo Bueno, J.; Goto, M.; Tsuneta, S.
2014ApJ...787..159I Altcode: 2014arXiv1404.0786I
Magnetic field measurements in the upper chromosphere and above,
where the gas-to-magnetic pressure ratio β is lower than unity,
are essential for understanding the thermal structure and dynamical
activity of the solar atmosphere. Recent developments in the theory and
numerical modeling of polarization in spectral lines have suggested
that information on the magnetic field of the chromosphere-corona
transition region could be obtained by measuring the linear polarization
of the solar disk radiation at the core of the hydrogen Lyα line at
121.6 nm, which is produced by scattering processes and the Hanle
effect. The Chromospheric Lyman-Alpha SpectroPolarimeter (CLASP)
sounding rocket experiment aims to measure the intensity (Stokes I)
and the linear polarization profiles (Q/I and U/I) of the hydrogen
Lyα line. In this paper, we clarify the information that the Hanle
effect can provide by applying a Stokes inversion technique based on
a database search. The database contains all theoretical Q/I and U/I
profiles calculated in a one-dimensional semi-empirical model of the
solar atmosphere for all possible values of the strength, inclination,
and azimuth of the magnetic field vector, though this atmospheric
region is highly inhomogeneous and dynamic. We focus on understanding
the sensitivity of the inversion results to the noise and spectral
resolution of the synthetic observations as well as the ambiguities and
limitation inherent to the Hanle effect when only the hydrogen Lyα is
used. We conclude that spectropolarimetric observations with CLASP can
indeed be a suitable diagnostic tool for probing the magnetism of the
transition region, especially when complemented with information on
the magnetic field azimuth that can be obtained from other instruments.
---------------------------------------------------------
Title: Depolarizing Collisions with Hydrogen: Neutral and Singly
Ionized Alkaline Earths
Authors: Manso Sainz, Rafael; Roncero, Octavio; Sanz-Sanz, Cristina;
Aguado, Alfredo; Asensio Ramos, Andrés; Trujillo Bueno, Javier
2014ApJ...788..118M Altcode: 2014arXiv1404.6339M
Depolarizing collisions are elastic or quasielastic collisions
that equalize the populations and destroy the coherence between
the magnetic sublevels of atomic levels. In astrophysical plasmas,
the main depolarizing collider is neutral hydrogen. We consider
depolarizing rates on the lowest levels of neutral and singly
ionized alkali earths Mg I, Sr I, Ba I, Mg II, Ca II, and Ba II,
due to collisions with H°. We compute ab initio potential curves of
the atom-H° system and solve the quantum mechanical dynamics. From
the scattering amplitudes, we calculate the depolarizing rates for
Maxwellian distributions of colliders at temperatures T <= 10,000
K. A comparative analysis of our results and previous calculations in
the literature is completed. We discuss the effect of these rates on
the formation of scattering polarization patterns of resonant lines
of alkali earths in the solar atmosphere, and their effect on Hanle
effect diagnostics of solar magnetic fields.
---------------------------------------------------------
Title: The transfer of resonance line polarization with partial
frequency redistribution and J-state interference. Theoretical
approach and numerical methods
Authors: Belluzzi, L.; Trujillo Bueno, J.
2014A&A...564A..16B Altcode: 2014arXiv1403.1701B
The linear polarization signals produced by scattering processes in
strong resonance lines are rich in information on the magnetic and
thermal structure of the chromosphere and transition region of the
Sun and of other stars. A correct modeling of these signals requires
accounting for partial frequency redistribution effects, as well
as for the impact of quantum interference between different fine
structure levels (J-state interference). In this paper, we present a
theoretical approach suitable for modeling the transfer of resonance
line polarization when taking these effects into account, along with an
accurate numerical method of solution of the problem's equations. We
consider a two-term atom with unpolarized lower term and infinitely
sharp lower levels, in the absence of magnetic fields. We show that
by making simple formal substitutions on the quantum numbers, the
theoretical approach derived here for a two-term atom can also be
applied to describe a two-level atom with hyperfine structure. An
illustrative application to the Mg ii doublet around 2800 Å is
presented.
---------------------------------------------------------
Title: Continuum polarization of stars as a result of occupation by
transiting exoplanets
Authors: Shchukina, N.; Frantseva, K.; Trujillo Bueno, J.
2014ysc..conf...12S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Time Evolution of Plasma Parameters during the Rise of a
Solar Prominence Instability
Authors: Orozco Suárez, D.; Díaz, A. J.; Asensio Ramos, A.; Trujillo
Bueno, J.
2014ApJ...785L..10O Altcode: 2014arXiv1403.5640O
We present high-spatial resolution spectropolarimetric observations
of a quiescent hedgerow prominence taken in the He I 1083.0 nm
triplet. The observation consisted of a time series in sit-and-stare
mode of ~36 minutes duration. The spectrograph's slit crossed the
prominence body and we recorded the time evolution of individual
vertical threads. Eventually, we observed the development of a dark
Rayleigh-Taylor plume that propagated upward with a velocity, projected
onto the plane of the sky, of 17 km s<SUP>-1</SUP>. Interestingly, the
plume apex collided with the prominence threads pushing them aside. We
inferred Doppler shifts, Doppler widths, and magnetic field strength
variations by interpreting the He I Stokes profiles with the HAZEL
code. The Doppler shifts show that clusters of threads move coherently
while individual threads have oscillatory patterns. Regarding the
plume we found strong redshifts (~9-12 km s<SUP>-1</SUP>) and large
Doppler widths (~10 km s<SUP>-1</SUP>) at the plume apex when it passed
through the prominence body and before it disintegrated. We associate
the redshifts with perspective effects while the Doppler widths are
more likely due to an increase in the local temperature. No local
variations of the magnetic field strength associated with the passage
of the plume were found; this leads us to conclude that the plumes are
no more magnetized than the surroundings. Finally, we found that some
of the threads' oscillations are locally damped, what allowed us to
apply prominence seismology techniques to infer additional prominence
physical parameters.
---------------------------------------------------------
Title: Non-coherent Continuum Scattering as a Line Polarization
Mechanism
Authors: del Pino Alemán, T.; Manso Sainz, R.; Trujillo Bueno, J.
2014ApJ...784...46D Altcode: 2014arXiv1401.8094D
Line scattering polarization can be strongly affected by Rayleigh
scattering at neutral hydrogen and Thomson scattering at free
electrons. Often a depolarization of the continuum results, but the
Doppler redistribution produced by the continuum scatterers, which
are light (hence, fast), induces more complex interactions between the
polarization in spectral lines and in the continuum. Here we formulate
and solve the radiative transfer problem of scattering line polarization
with non-coherent continuum scattering consistently. The problem is
formulated within the spherical tensor representation of atomic and
light polarization. The numerical method of solution is a generalization
of the Accelerated Lambda Iteration that is applied to both the atomic
system and the radiation field. We show that the redistribution of
the spectral line radiation due to the non-coherence of the continuum
scattering may modify the shape of the emergent fractional linear
polarization patterns significantly, even yielding polarization signals
above the continuum level in intrinsically unpolarizable lines.
---------------------------------------------------------
Title: Chromospheric Lyman-alpha spectro-polarimeter (CLASP)
Authors: Kano, Ryouhei; Katsukawa, Yukio; Kubo, Masahito; Auchere,
Frederic; Ishikawa, Ryohko; Kobayashi, Ken; Narukage, Noriyuki;
Trujillo Bueno, Javier; Bando, Takamasa; Ishikawa, Shin-nosuke
2014cosp...40E1383K Altcode:
In the solar chromosphere, magneto-hydrodynamic waves and super-sonic
jets ubiquitously happen as revealed by the Japanese solar satellite
Hinode. Now, we understand that the solar chromosphere is not a simple
intermediate layer smoothly connecting the photosphere and corona,
but a site where those dynamics may play an important role in the
chromospheric and coronal heating. Such discoveries imply that the
next frontier in solar physics lies in simultaneous observations
between the dynamics and magnetic structures in the chromosphere and
transition region, where the gas-dominant photosphere changes to the
magnetic-dominant corona. Therefore, we promote the Chromospheric
Lyman-Alpha SpectroPolarimeter (CLASP), which is a NASA's sounding
rocket experiment scheduled in 2015 for aiming to infer the magnetic
field information in the solar chromosphere and transition region. CLASP
makes precise measurement (0.1%) of the polarization profile of the
Lyman-alpha line, and aims to make the first ever measurement of the
Hanle effect polarization caused by magnetic fields in the upper solar
atmosphere. It is also a pathfinder to establish a new measurement
tool for chromospheric and transition-region magnetic fields, and to
make progress on chromospheric studies in future missions.
---------------------------------------------------------
Title: Polarized Radiation Diagnostics for Exploring the Magnetic
Activity of the Chromosphere, Transition Region and Corona
Authors: Trujillo Bueno, Javier
2014cosp...40E3395T Altcode:
In order to investigate the magnetic activity of the chromosphere,
transition region and corona of the Sun we need (1) to identify
observables sensitive to the magnetic fields of such outer atmospheric
regions, (2) to build the telescopes and instruments needed for
measuring the observables, and (3) to develop suitable plasma
diagnostic techniques to infer the relevant physical quantities from
the observables (e.g., the strength and orientation of the magnetic
field). Here I critically review old and recent investigations on the
polarization produced by anisotropic radiation pumping and the Hanle and
Zeeman effects in selected IR, FUV and EUV spectral lines, showing their
sensitivity to the presence of a magnetic field in the chromosphere,
transition region and corona. I argue that spectropolarimetry from
ground-based and space telescopes is indeed our key gateway for the
exploration of the magnetic activity of the outer solar atmosphere,
but I also emphasize that we need novel breakthroughs in the development
of instruments and polarized radiation diagnostics to achieve such goal.
---------------------------------------------------------
Title: A first look into the magnetic field configuration of
prominence threads using spectropolarimetric data
Authors: Orozco Suárez, D.; Asensio Ramos, A.; Trujillo Bueno, J.
2014IAUS..300..112O Altcode: 2014IAUS..300..112S; 2013arXiv1310.0257O
We show preliminary results of an ongoing investigation aimed at
determining the configuration of the magnetic field vector in the
threads of a quiescent hedgerow solar prominence using high-spatial
resolution spectropolarimetric observations taken in the He I 1083.0
nm multiplet. The data consist of a two-dimensional map of a quiescent
hedgerow prominence showing vertical threads. The observations were
obtained with the Tenerife Infrared Polarimeter attached to the German
Vacuum Tower Telescope at the Observatorio del Teide (Spain). The He
I 1083.0 nm Stokes signals are interpreted with an inversion code,
which takes into account the key physical processes that generate
and/or modify circular and linear polarization signals in the He I
1083.0 nm triplet: the Zeeman effect, anisotropic radiation pumping,
and the Hanle effect. We present initial results of the inversions,
i.e, the strength and orientation of the magnetic field vector along
the prominence and in prominence threads.
---------------------------------------------------------
Title: A Key Physical Mechanism for Understanding the Enigmatic
Linear Polarization of the Solar Ba II and Na I D<SUB>1</SUB> Lines
Authors: Belluzzi, Luca; Trujillo Bueno, Javier
2013ApJ...774L..28B Altcode: 2013arXiv1308.5422B
The linearly polarized spectrum of the solar limb radiation produced by
scattering processes is of great diagnostic potential for exploring the
magnetism of the solar atmosphere. This spectrum shows an impressive
richness of spectral details and enigmatic Q/I signals, whose physical
origin must be clearly understood before they can be exploited for
diagnostic purposes. The most enduring enigma is represented by the
polarization signals observed in the D<SUB>1</SUB> resonance lines
of Na I (5896 Å) and Ba II (4934 Å), which were expected to be
intrinsically unpolarizable. The totality of sodium and 18% of barium
have hyperfine structure (HFS), and it has been argued that the only way
to produce a scattering polarization signal in such lines is through
the presence of a substantial amount of atomic polarization in their
lower HFS levels. The strong sensitivity of these long-lived levels
to depolarizing mechanisms led to the paradoxical conclusion that
the observed D<SUB>1</SUB>-line polarization is incompatible with the
presence in the lower solar chromosphere of inclined magnetic fields
sensibly stronger than 0.01 G. Here we show that by properly taking
into account the fact that the solar D<SUB>1</SUB>-line radiation has
a non-negligible spectral structure over the short frequency interval
spanned by the HFS transitions, it is possible to produce scattering
polarization signals in the D<SUB>1</SUB> lines of Na I and Ba II
without the need of ground-level polarization. The resulting linear
polarization is not so easily destroyed by elastic collisions and/or
magnetic fields.
---------------------------------------------------------
Title: PORTA: A three-dimensional multilevel radiative transfer code
for modeling the intensity and polarization of spectral lines with
massively parallel computers
Authors: Štěpán, Jiří; Trujillo Bueno, Javier
2013A&A...557A.143S Altcode: 2013arXiv1307.4217S
The interpretation of the intensity and polarization of the spectral
line radiation produced in the atmosphere of the Sun and of other stars
requires solving a radiative transfer problem that can be very complex,
especially when the main interest lies in modeling the spectral line
polarization produced by scattering processes and the Hanle and Zeeman
effects. One of the difficulties is that the plasma of a stellar
atmosphere can be highly inhomogeneous and dynamic, which implies the
need to solve the non-equilibrium problem of the generation and transfer
of polarized radiation in realistic three-dimensional (3D) stellar
atmospheric models. Here we present PORTA, an efficient multilevel
radiative transfer code we have developed for the simulation of the
spectral line polarization caused by scattering processes and the Hanle
and Zeeman effects in 3D models of stellar atmospheres. The numerical
method of solution is based on the non-linear multigrid iterative method
and on a novel short-characteristics formal solver of the Stokes-vector
transfer equation which uses monotonic Bézier interpolation. Therefore,
with PORTA the computing time needed to obtain at each spatial grid
point the self-consistent values of the atomic density matrix (which
quantifies the excitation state of the atomic system) scales linearly
with the total number of grid points. Another crucial feature of PORTA
is its parallelization strategy, which allows us to speed up the
numerical solution of complicated 3D problems by several orders of
magnitude with respect to sequential radiative transfer approaches,
given its excellent linear scaling with the number of available
processors. The PORTA code can also be conveniently applied to solve
the simpler 3D radiative transfer problem of unpolarized radiation in
multilevel systems.
---------------------------------------------------------
Title: Chromospheric Lyman Alpha SpectroPolarimeter: CLASP
Authors: Kobayashi, Ken; Kano, R.; Trujillo Bueno, J.; Winebarger,
A. R.; Cirtain, J. W.; Bando, T.; De Pontieu, B.; Ishikawa, R.;
Katsukawa, Y.; Kubo, M.; Narukage, N.; Sakao, T.; Tsuneta, S.;
Auchère, F.; Asensio Ramos, A.; Belluzzi, L.; Carlsson, M.; Casini,
R.; Hara, H.; Ichimoto, K.; Manso Sainz, R.; Shimizu, T.; Stepan,
J.; Suematsu, Y.; Holloway, T.
2013SPD....44..142K Altcode:
The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) is a VUV
spectropolarimeter optimized for measuring the linear polarization of
the Lyman-alpha line (121.6 nm). The Lyman-alpha line is predicted to
show linear polarization caused by atomic scattering in the chromosphere
and modified by the magnetic field through the Hanle effect. The
Hanle effect is sensitive to weaker magnetic fields than Zeeman
effect, and is not canceled by opposing fields, making it sensitive
to tangled or unresolved magnetic field structures. These factors make
the Hanle effect a valuable tool for probing the magnetic field in the
chromosphere above the quiet sun. To meet this goal, CLASP is designed
to measure linear polarization with 0.1% polarization sensitivity
at 0.01 nm spectral resolution and 10" spatial resolution. CLASP is
scheduled to be launched in 2015.
---------------------------------------------------------
Title: Spectropolarimetric diagnostics of unresolved magnetic fields
in the quiet solar photosphere
Authors: Shchukina, Nataliya G.; Trujillo Bueno, Javier
2013IAUS..294..107S Altcode: 2012arXiv1212.3048S
A few years before the Hinode space telescope was launched, an
investigation based on the Hanle effect in atomic and molecular lines
indicated that the bulk of the quiet solar photosphere is significantly
magnetized, due to the ubiquitous presence of an unresolved magnetic
field with an average strength <B>, ~ 130 G. It was pointed
out also that this “hidden” field must be much stronger in the
intergranular regions of solar surface convection than in the granular
regions, and it was suggested that this unresolved magnetic field
could perhaps provide the clue for understanding how the outer solar
atmosphere is energized. In fact, the ensuing magnetic energy density is
so significant that the energy flux estimated using the typical value of
1 km/s for the convective velocity (thinking in rising magnetic loops)
or the Alfvén speed (thinking in Alfvén waves generated by magnetic
reconnection) turns out to be substantially larger than that required to
balance the chromospheric energy losses. Here we present a brief review
of the research that led to such conclusions, with emphasis on a new
three-dimensional radiative transfer investigation aimed at determining
the magnetization of the quiet Sun photosphere from the Hanle effect
in the Sr I 4607 Å line and the Zeeman effect in Fe I lines.
---------------------------------------------------------
Title: Measuring vector magnetic fields in solar prominences
Authors: Orozco Suárez, D.; Asensio Ramos, A.; Trujillo Bueno, J.
2013hsa7.conf..786O Altcode: 2012arXiv1211.2119O
We present spectropolarimetric observations in the He I 1083.0 nm
multiplet of a quiescent, hedgerow solar prominence. The data were taken
with the Tenerife Infrared Polarimeter attached to the German Vacuum
Tower Telescope at the Observatorio del Teide (Tenerife; Canary Islands;
Spain). The observed He I circular and linear polarization signals
are dominated by the Zeeman effect and by atomic level polarization
and the Hanle effect, respectively. These observables are sensitive
to the strength and orientation of the magnetic field vector at each
spatial point of the field of view. We determine the magnetic field
vector of the prominence by applying the HAZEL inversion code to the
observed Stokes profiles. We briefly discuss the retrieved magnetic
field vector configuration.
---------------------------------------------------------
Title: Theoretical formulation of Doppler redistribution in scattering
polarization within the framework of the velocity-space density
matrix formalism
Authors: Belluzzi, L.; Landi Degl'Innocenti, E.; Trujillo Bueno, J.
2013A&A...552A..72B Altcode: 2013arXiv1302.2887B
Within the framework of the density matrix theory for the generation and
transfer of polarized radiation, velocity density matrix correlations
represent an important physical aspect that, however, is often neglected
in practical applications when adopting the simplifying approximation
of complete redistribution on velocity. In this paper, we present an
application of the non-LTE problem for polarized radiation taking
such correlations into account through the velocity-space density
matrix formalism. We consider a two-level atom with infinitely sharp
upper and lower levels, and we derive the corresponding statistical
equilibrium equations, neglecting the contribution of velocity-changing
collisions. Coupling such equations with the radiative transfer
equations for polarized radiation, we derive a set of coupled equations
for the velocity-dependent source function. This set of equations is
then particularized to the case of a plane-parallel atmosphere. The
equations presented in this paper provide a complete and solid
description of the physics of pure Doppler redistribution, a phenomenon
generally described within the framework of the redistribution matrix
formalism. The redistribution matrix corresponding to this problem
(generally referred to as R<SUB>I</SUB>) is derived starting from the
statistical equilibrium equations for the velocity-space density matrix
and from the radiative transfer equations for polarized radiation,
thus showing the equivalence of the two approaches.
---------------------------------------------------------
Title: Isotropic inelastic and superelastic collisional rates in a
multiterm atom
Authors: Belluzzi, L.; Landi Degl'Innocenti, E.; Trujillo Bueno, J.
2013A&A...551A..84B Altcode: 2013arXiv1302.0990B
The spectral line polarization of the radiation emerging from a
magnetized astrophysical plasma depends on the state of the atoms
within the medium, whose determination requires considering the
interactions between the atoms and the magnetic field, between the
atoms and photons (radiative transitions), and between the atoms and
other material particles (collisional transitions). In applications
within the framework of the multiterm model atom (which accounts for
quantum interference between magnetic sublevels pertaining either
to the same J-level or to different J-levels within the same term)
collisional processes are generally neglected when solving the master
equation for the atomic density matrix. This is partly due to the lack
of experimental data and/or of approximate theoretical expressions for
calculating the collisional transfer and relaxation rates (in particular
the rates for interference between sublevels pertaining to different
J-levels, and the depolarizing rates due to elastic collisions). In this
paper we formally define and investigate the transfer and relaxation
rates due to isotropic inelastic and superelastic collisions that enter
the statistical equilibrium equations for the atomic density matrix of
a multiterm atom. Under the hypothesis that the interaction between
the collider and the atom can be described by a dipolar operator, we
provide expressions that relate the collisional rates for interference
between different J-levels to the usual collisional rates for J-level
populations, for which experimental data or approximate theoretical
expressions are generally available. We show that the rates for
populations and interference within the same J-level reduce to those
previously obtained for the multilevel model atom (where quantum
interference is assumed to be present only between magnetic sublevels
pertaining to any given J-level). Finally, we apply the general
equations to the case of a two-term atom with unpolarized lower term,
illustrating the impact of inelastic and superelastic collisions on the
scattering line polarization through radiative transfer calculations
in a slab of stellar atmospheric plasma anisotropically illuminated
by the photospheric radiation field.
---------------------------------------------------------
Title: Temporal Evolution of the Scattering Polarization of the Ca
II IR Triplet in Hydrodynamical Models of the Solar Chromosphere
Authors: Carlin, E. S.; Asensio Ramos, A.; Trujillo Bueno, J.
2013ApJ...764...40C Altcode: 2012arXiv1210.1525C
Velocity gradients in a stellar atmospheric plasma have an effect
on the anisotropy of the radiation field that illuminates each
point within the medium, and this may in principle influence the
scattering line polarization that results from the induced atomic level
polarization. Here, we analyze the emergent linear polarization profiles
of the Ca II infrared triplet after solving the radiative transfer
problem of scattering polarization in time-dependent hydrodynamical
models of the solar chromosphere, taking into account the effect of the
plasma macroscopic velocity on the atomic level polarization. We discuss
the influence that the velocity and temperature shocks in the considered
chromospheric models have on the temporal evolution of the scattering
polarization signals of the Ca II infrared lines as well as on the
temporally averaged profiles. Our results indicate that the increase
of the linear polarization amplitudes caused by macroscopic velocity
gradients may be significant in realistic situations. We also study
the effect of the integration time, the microturbulent velocity, and
the photospheric dynamical conditions, and discuss the feasibility of
observing with large-aperture telescopes the temporal variation of the
scattering polarization profiles. Finally, we explore the possibility
of using a Hanle effect line-ratio technique in the IR triplet of Ca
II to facilitate magnetic field diagnostics in dynamic situations.
---------------------------------------------------------
Title: Evidence for Rotational Motions in the Feet of a Quiescent
Solar Prominence
Authors: Orozco Suárez, D.; Asensio Ramos, A.; Trujillo Bueno, J.
2012ApJ...761L..25O Altcode: 2012arXiv1211.6980O
We present observational evidence of apparent plasma rotational motions
in the feet of a solar prominence. Our study is based on spectroscopic
observations taken in the He I 1083.0 nm multiplet with the Tenerife
Infrared Polarimeter attached to the German Vacuum Tower Telescope. We
recorded a time sequence of spectra with 34 s cadence placing the slit
of the spectrograph almost parallel to the solar limb and crossing two
feet of an intermediate size, quiescent hedgerow prominence. The data
show opposite Doppler shifts, ±6 km s<SUP>-1</SUP>, at the edges of
the prominence feet. We argue that these shifts may be interpreted as
prominence plasma rotating counterclockwise around the vertical axis to
the solar surface as viewed from above. The evolution of the prominence
seen in EUV images taken with the Solar Dynamics Observatory provided
us with clues to interpret the results as swirling motions. Moreover,
time-distance images taken far from the central wavelength show
plasma structures moving parallel to the solar limb with velocities
of about 10-15 km s<SUP>-1</SUP>. Finally, the shapes of the observed
intensity profiles suggest the presence of, at least, two components
at some locations at the edges of the prominence feet. One of them is
typically Doppler shifted (up to ~20 km s<SUP>-1</SUP>) with respect to
the other, thus suggesting the existence of supersonic counter-streaming
flows along the line of sight.
---------------------------------------------------------
Title: Polarized Radiation Diagnostics for Measuring the Magnetic
Field of the Outer Solar Atmosphere
Authors: Trujillo Bueno, J.
2012IAUSS...6E.302T Altcode:
The basic idea of optical pumping, for which Alfred Kastler
received the 1966 Nobel Prize in physics, is that the absorption and
scattering of light that is near-resonant with an optical transition
can produce large population imbalances among the magnetic sublevels
of atomic ground states as well as in excited states. The degree of
this radiatively-induced atomic level polarization, which is very
sensitive to the presence of magnetic fields, can be determined by
observing the polarization of the scattered or transmitted spectral
line radiation. Probably, the most important point for solar physics is
that the outer solar atmosphere is indeed an optically pumped vapor and
that the polarization of the emergent spectral line radiation can be
exploited for detecting magnetic fields that are too weak and/or too
tangled so as to produce measurable Zeeman polarization signals. In
this talk we review some recent radiative transfer simulations of
the polarization produced by optical pumping in selected IR, FUV
and EUV spectral lines, showing that their sensitivity to the Hanle
effect is very suitable for magnetic field measurements in the outer
solar atmosphere. We argue that solar magnetometry using the spectral
lines of optically pumped atoms in the chromosphere, transition region
and corona should be a high-priority goal for large aperture solar
telescopes, such as ATST, EST and SOLAR-C.
---------------------------------------------------------
Title: LEMUR: Large European module for solar Ultraviolet
Research. European contribution to JAXA's Solar-C mission
Authors: Teriaca, Luca; Andretta, Vincenzo; Auchère, Frédéric;
Brown, Charles M.; Buchlin, Eric; Cauzzi, Gianna; Culhane, J. Len;
Curdt, Werner; Davila, Joseph M.; Del Zanna, Giulio; Doschek, George
A.; Fineschi, Silvano; Fludra, Andrzej; Gallagher, Peter T.; Green,
Lucie; Harra, Louise K.; Imada, Shinsuke; Innes, Davina; Kliem,
Bernhard; Korendyke, Clarence; Mariska, John T.; Martínez-Pillet,
Valentin; Parenti, Susanna; Patsourakos, Spiros; Peter, Hardi; Poletto,
Luca; Rutten, Robert J.; Schühle, Udo; Siemer, Martin; Shimizu,
Toshifumi; Socas-Navarro, Hector; Solanki, Sami K.; Spadaro, Daniele;
Trujillo-Bueno, Javier; Tsuneta, Saku; Dominguez, Santiago Vargas;
Vial, Jean-Claude; Walsh, Robert; Warren, Harry P.; Wiegelmann,
Thomas; Winter, Berend; Young, Peter
2012ExA....34..273T Altcode: 2011ExA...tmp..135T; 2011arXiv1109.4301T
The solar outer atmosphere is an extremely dynamic environment
characterized by the continuous interplay between the plasma and the
magnetic field that generates and permeates it. Such interactions play a
fundamental role in hugely diverse astrophysical systems, but occur at
scales that cannot be studied outside the solar system. Understanding
this complex system requires concerted, simultaneous solar observations
from the visible to the vacuum ultraviolet (VUV) and soft X-rays, at
high spatial resolution (between 0.1” and 0.3”), at high temporal
resolution (on the order of 10 s, i.e., the time scale of chromospheric
dynamics), with a wide temperature coverage (0.01 MK to 20 MK,
from the chromosphere to the flaring corona), and the capability of
measuring magnetic fields through spectropolarimetry at visible and
near-infrared wavelengths. Simultaneous spectroscopic measurements
sampling the entire temperature range are particularly important. These
requirements are fulfilled by the Japanese Solar-C mission (Plan B),
composed of a spacecraft in a geosynchronous orbit with a payload
providing a significant improvement of imaging and spectropolarimetric
capabilities in the UV, visible, and near-infrared with respect to
what is available today and foreseen in the near future. The Large
European Module for solar Ultraviolet Research (LEMUR), described
in this paper, is a large VUV telescope feeding a scientific payload
of high-resolution imaging spectrographs and cameras. LEMUR consists
of two major components: a VUV solar telescope with a 30 cm diameter
mirror and a focal length of 3.6 m, and a focal-plane package composed
of VUV spectrometers covering six carefully chosen wavelength ranges
between 170 Å and 1270 Å. The LEMUR slit covers 280” on the Sun with
0.14” per pixel sampling. In addition, LEMUR is capable of measuring
mass flows velocities (line shifts) down to 2 km s<SUP> - 1</SUP> or
better. LEMUR has been proposed to ESA as the European contribution
to the Solar C mission.
---------------------------------------------------------
Title: The Hanle Effect of Lyα in a Magnetohydrodynamic Model of
the Solar Transition Region
Authors: Štěpán, J.; Trujillo Bueno, J.; Carlsson, M.; Leenaarts, J.
2012ApJ...758L..43S Altcode: 2012arXiv1208.4929S
In order to understand the heating of the solar corona it is crucial
to obtain empirical information on the magnetic field in its lower
boundary (the transition region). To this end, we need to measure
and model the linear polarization produced by scattering processes in
strong UV lines, such as the hydrogen Lyα line. The interpretation
of the observed Stokes profiles will require taking into account that
the outer solar atmosphere is highly structured and dynamic, and that
the height of the transition region may well vary from one place in
the atmosphere to another. Here, we report on the Lyα scattering
polarization signals we have calculated in a realistic model of an
enhanced network region, resulting from a state-of-the-art radiation
magnetohydrodynamic simulation. This model is characterized by spatially
complex variations of the physical quantities at transition region
heights. The results of our investigation lead us to emphasize that
scattering processes in the upper solar chromosphere should indeed
produce measurable linear polarization in Lyα. More importantly,
we show that via the Hanle effect the model's magnetic field produces
significant changes in the emergent Q/I and U/I profiles. Therefore, we
argue that by measuring the polarization signals produced by scattering
processes and the Hanle effect in Lyα and contrasting them with those
computed in increasingly realistic atmospheric models, we should be
able to decipher the magnetic, thermal, and dynamic structure of the
upper chromosphere and transition region of the Sun.
---------------------------------------------------------
Title: Chromospheric Lyman-alpha spectro-polarimeter (CLASP)
Authors: Kano, Ryouhei; Bando, Takamasa; Narukage, Noriyuki; Ishikawa,
Ryoko; Tsuneta, Saku; Katsukawa, Yukio; Kubo, Masahito; Ishikawa,
Shin-nosuke; Hara, Hirohisa; Shimizu, Toshifumi; Suematsu, Yoshinori;
Ichimoto, Kiyoshi; Sakao, Taro; Goto, Motoshi; Kato, Yoshiaki; Imada,
Shinsuke; Kobayashi, Ken; Holloway, Todd; Winebarger, Amy; Cirtain,
Jonathan; De Pontieu, Bart; Casini, Roberto; Trujillo Bueno, Javier;
Štepán, Jiří; Manso Sainz, Rafael; Belluzzi, Luca; Asensio Ramos,
Andres; Auchère, Frédéric; Carlsson, Mats
2012SPIE.8443E..4FK Altcode:
One of the biggest challenges in heliophysics is to decipher the
magnetic structure of the solar chromosphere. The importance of
measuring the chromospheric magnetic field is due to both the key role
the chromosphere plays in energizing and structuring the outer solar
atmosphere and the inability of extrapolation of photospheric fields to
adequately describe this key boundary region. Over the last few years,
significant progress has been made in the spectral line formation
of UV lines as well as the MHD modeling of the solar atmosphere. It
is found that the Hanle effect in the Lyman-alpha line (121.567 nm)
is a most promising diagnostic tool for weaker magnetic fields in
the chromosphere and transition region. Based on this groundbreaking
research, we propose the Chromospheric Lyman-Alpha Spectro-Polarimeter
(CLASP) to NASA as a sounding rocket experiment, for making the first
measurement of the linear polarization produced by scattering processes
and the Hanle effect in the Lyman-alpha line (121.567 nm), and making
the first exploration of the magnetic field in the upper chromosphere
and transition region of the Sun. The CLASP instrument consists
of a Cassegrain telescope, a rotating 1/2-wave plate, a dual-beam
spectrograph assembly with a grating working as a beam splitter, and
an identical pair of reflective polarization analyzers each equipped
with a CCD camera. We propose to launch CLASP in December 2014.
---------------------------------------------------------
Title: The Scattering Polarization of the Lyα Lines of H I and He
II Taking into Account Partial Frequency Redistribution and J-state
Interference Effects
Authors: Belluzzi, Luca; Trujillo Bueno, Javier; Štěpán, Jiří
2012ApJ...755L...2B Altcode: 2012arXiv1207.0415B
Recent theoretical investigations have pointed out that the cores of
the Lyα lines of H I and He II should show measurable scattering
polarization signals when observing the solar disk, and that the
magnetic sensitivity, through the Hanle effect, of such linear
polarization signals is suitable for exploring the magnetism of the
solar transition region. Such investigations were carried out in the
limit of complete frequency redistribution (CRD) and neglecting quantum
interference between the two upper J-levels of each line. Here we relax
both approximations and show that the joint action of partial frequency
redistribution and J-state interference produces much more complex
fractional linear polarization (Q/I) profiles, with large amplitudes
in their wings. Such wing polarization signals turn out to be very
sensitive to the temperature structure of the atmospheric model, so
that they can be exploited for constraining the thermal properties of
the solar chromosphere. Finally, we show that the approximation of CRD
without J-state interference is however suitable for estimating the
amplitude of the linear polarization signals in the core of the lines,
where the Hanle effect operates.
---------------------------------------------------------
Title: Non-LTE Determination of the Silicon Abundance Using a
Three-dimensional Hydrodynamical Model of the Solar Photosphere
Authors: Shchukina, N.; Sukhorukov, A.; Trujillo Bueno, J.
2012ApJ...755..176S Altcode:
Confrontations of spectroscopic observations with local thermodynamic
equilibrium (LTE) spectral syntheses in a three-dimensional (3D)
hydrodynamical model of the solar photosphere led to a downward
revision of the photospheric and meteoritic silicon abundances. Here we
derive the photospheric silicon abundance taking into account non-LTE
(NLTE) effects in the same 3D model. We show that the above-mentioned
downward revision of the silicon abundance is caused by using the LTE
approximation in the context of 3D modeling, an experimental scale of
oscillator strengths, and a small number of Si I lines. We demonstrate
that no revision of the solar silicon abundance is required if NLTE
effects are taken into account and one uses a "solar" oscillator
strength scale and an extended list of Si I lines. The NLTE abundance
value we find by fitting the equivalent widths of 65 Si I lines is
A <SUP>NLTE</SUP> <SUB>Si</SUB> = 7.549 ± 0.016. This value agrees
well with the silicon abundance that had been recommended earlier by
Grevesse & Sauval and Lodders for the solar photosphere and CI
chondrite meteorites.
---------------------------------------------------------
Title: Scattering Polarization in the Ca II Infrared Triplet with
Velocity Gradients
Authors: Carlin, E. S.; Manso Sainz, R.; Asensio Ramos, A.; Trujillo
Bueno, J.
2012ApJ...751....5C Altcode: 2012arXiv1203.4438C
Magnetic field topology, thermal structure, and plasma motions are the
three main factors affecting the polarization signals used to understand
our star. In this theoretical investigation, we focus on the effect
that gradients in the macroscopic vertical velocity field have on the
non-magnetic scattering polarization signals, establishing the basis for
general cases. We demonstrate that the solar plasma velocity gradients
may have a significant effect on the linear polarization produced by
scattering in chromospheric spectral lines. In particular, we show the
impact of velocity gradients on the anisotropy of the radiation field
and on the ensuing fractional alignment of the Ca II levels, and how
they can lead to an enhancement of the zero-field linear polarization
signals. This investigation remarks on the importance of knowing
the dynamical state of the solar atmosphere in order to correctly
interpret spectropolarimetric measurements, which is important, among
other things, for establishing a suitable zero-field reference case
to infer magnetic fields via the Hanle effect.
---------------------------------------------------------
Title: The Chromospheric Lyman-Alpha SpectroPolarimeter: CLASP
Authors: Kobayashi, K.; Kano, R.; Trujillo-Bueno, J.; Asensio Ramos,
A.; Bando, T.; Belluzzi, L.; Carlsson, M.; De Pontieu, R. C. B.; Hara,
H.; Ichimoto, K.; Ishikawa, R.; Katsukawa, Y.; Kubo, M.; Manso Sainz,
R.; Narukage, N.; Sakao, T.; Stepan, J.; Suematsu, Y.; Tsuneta, S.;
Watanabe, H.; Winebarger, A.
2012ASPC..456..233K Altcode:
The magnetic field plays a crucial role in the chromosphere and the
transition region, and our poor empirical knowledge of the magnetic
field in the upper chromosphere and transition region is a major
impediment to advancing the understanding of the solar atmosphere. The
Hanle effect promises to be a valuable alternative to Zeeman effect
as a method of measuring the magnetic field in the chromosphere and
transition region; it is sensitive to weaker magnetic fields, and
also sensitive to tangled, unresolved field structures. <P />CLASP
is a sounding rocket experiment that aims to observe the Hanle effect
polarization of the Lyman α (1215.67Å) line in the solar chromosphere
and transition region, and prove the usefulness of this technique in
placing constraints on the magnetic field strength and orientation
in the low plasma-β region of the solar atmosphere. The Ly-α line
has been chosen because it is a chromospheric/transition-region line,
and because the Hanle effect polarization of this line is predicted to
be sensitive to 10-250 Gauss, encompassing the range of interest. The
CLASP instrument is designed to measure linear polarization in the
Ly-α line with a polarization sensitivity of 0.1%. The instrument is
currently funded for development. The optical design of the instrument
has been finalized, and an extensive series of component-level tests
are underway to validate the design.
---------------------------------------------------------
Title: The Polarization of the Solar Mg II h and k Lines
Authors: Belluzzi, Luca; Trujillo Bueno, Javier
2012ApJ...750L..11B Altcode: 2012arXiv1203.4351B
Although the h and k lines of Mg II are expected to be of great interest
for probing the upper solar chromosphere, relatively little is known
about their polarization properties which encode the information on the
magnetic field. Here we report the first results of an investigation
whose main goal is to understand the physical mechanisms that control
the scattering polarization across these resonance lines and to
achieve a realistic radiative transfer modeling in the presence of
arbitrary magnetic fields. We show that the joint action of partial
frequency redistribution (PRD) and quantum interference between
the upper J-levels of the two lines produces a complex fractional
linear polarization (Q/I) pattern with large polarization amplitudes
in the blue and red wings, and a negative feature in the spectral
region between the two lines. Another remarkable peculiarity of the
Q/I profile is a conspicuous antisymmetric signal around the center
of the h line, which cannot be obtained unless both PRD and J-state
interference effects are taken into account. In the core of the k line,
PRD effects alone produce a triplet peak structure in the Q/I profile,
the modeling of which can also be achieved via the two-level atom
approximation. In addition to the Hanle effect in the core of the
k line, we also emphasize the diagnostic potential of the circular
polarization produced by the Zeeman effect in the h and k lines,
as well as in other Mg II lines located in their wings.
---------------------------------------------------------
Title: The Hanle Effect in the Lyα Lines of H I and He II for
Measuring the Magnetic Fields of the Solar Transition Region
Authors: Trujillo Bueno, J.; Štepán, J.; Belluzzi, L.
2012ASPC..456..225T Altcode: 2012ASPC..456..225B
The Ly α lines of H I and He II are two of the spectral lines of choice
for FUV and EUV channels of narrowband imagers on board sounding rockets
and space telescopes, which provide spectacular intensity images of the
outer solar atmosphere. Since the magnetic field information is encoded
in the polarization of the spectral line radiation, it is important
to investigate whether the ensuing Ly α radiation from the solar disk
can be polarized, along with its magnetic sensitivity. Here we present
some theoretical predictions concerning the amplitudes and magnetic
sensitivities of the linear polarization signals produced by scattering
processes in these strong emission lines of the solar transition region,
taking into account radiative transfer and the Hanle effect caused by
the presence of organized and random magnetic fields. We find that the
line-center amplitudes of the fractional polarization signals vary
typically between a fraction of a percent and ∼1%, depending on
the Ly α line under consideration, the scattering geometry and the
strength and orientation of the magnetic field. Interestingly, while
the Ly α line of He II starts to be sensitive to the Hanle effect
for magnetic strengths B>̰100 G the hydrogen Lyα line is mainly
sensitive to magnetic strengths between 10 and 100 G. These results
encourage the development of FUV and EUV polarimeters for sounding
rockets and space telescopes with the aim of opening up a diagnostic
window for magnetic field measurements in the upper chromosphere and
transition region of the Sun.
---------------------------------------------------------
Title: A 3D Radiative Transfer Code for Modeling the Hanle Effect
in the Lyman α line
Authors: Štepán, J.; Trujillo Bueno, J.
2012ASPC..456...59S Altcode: 2012arXiv1205.2959S
In order to obtain empirical information on the magnetism of the
solar transition region we need to measure and interpret the linear
polarization produced by scattering processes in FUV and EUV spectral
lines. Via the Hanle effect such linear polarization signals are
sensitive to the magnetic fields expected for the quiet and active
regions of the outer solar atmosphere. For example, the Ly$\alpha$ line
of H\,{\sc i} at 1216\,Å is mainly sensitive to magnetic strengths
between 10 and 100 G. The interpretation of the observed spectral
line polarization requires the development of suitable modeling
tools. To this end, we have developed a three-dimensional (3D),
non-LTE multilevel radiative transfer code for modeling the intensity
and linear polarization produced by scattering processes in spectral
lines and its modification by the Hanle effect.
---------------------------------------------------------
Title: Solar magnetism eXplorer (SolmeX). Exploring the magnetic
field in the upper atmosphere of our closest star
Authors: Peter, Hardi; Abbo, L.; Andretta, V.; Auchère, F.; Bemporad,
A.; Berrilli, F.; Bommier, V.; Braukhane, A.; Casini, R.; Curdt,
W.; Davila, J.; Dittus, H.; Fineschi, S.; Fludra, A.; Gandorfer, A.;
Griffin, D.; Inhester, B.; Lagg, A.; Landi Degl'Innocenti, E.; Maiwald,
V.; Sainz, R. Manso; Martínez Pillet, V; Matthews, S.; Moses, D.;
Parenti, S.; Pietarila, A.; Quantius, D.; Raouafi, N. -E.; Raymond, J.;
Rochus, P.; Romberg, O.; Schlotterer, M.; Schühle, U.; Solanki, S.;
Spadaro, D.; Teriaca, L.; Tomczyk, S.; Trujillo Bueno, J.; Vial, J. -C.
2012ExA....33..271P Altcode: 2011arXiv1108.5304P; 2011ExA...tmp..134P
The magnetic field plays a pivotal role in many fields of
Astrophysics. This is especially true for the physics of the solar
atmosphere. Measuring the magnetic field in the upper solar atmosphere
is crucial to understand the nature of the underlying physical
processes that drive the violent dynamics of the solar corona—that
can also affect life on Earth. SolmeX, a fully equipped solar space
observatory for remote-sensing observations, will provide the first
comprehensive measurements of the strength and direction of the
magnetic field in the upper solar atmosphere. The mission consists
of two spacecraft, one carrying the instruments, and another one in
formation flight at a distance of about 200 m carrying the occulter to
provide an artificial total solar eclipse. This will ensure high-quality
coronagraphic observations above the solar limb. SolmeX integrates two
spectro-polarimetric coronagraphs for off-limb observations, one in
the EUV and one in the IR, and three instruments for observations on
the disk. The latter comprises one imaging polarimeter in the EUV for
coronal studies, a spectro-polarimeter in the EUV to investigate the low
corona, and an imaging spectro-polarimeter in the UV for chromospheric
studies. SOHO and other existing missions have investigated the emission
of the upper atmosphere in detail (not considering polarization),
and as this will be the case also for missions planned for the near
future. Therefore it is timely that SolmeX provides the final piece of
the observational quest by measuring the magnetic field in the upper
atmosphere through polarimetric observations.
---------------------------------------------------------
Title: Observables for Measuring the Outer-Atmospheric Magnetic
Field from Chromosphere to Corona
Authors: Trujillo Bueno, J.; et al.
2012decs.confE..35T Altcode:
The basic idea of optical pumping, for which Alfred Kastler received
the 1966 Nobel Prize in physics, is that the absorption and scattering
of light that is near-resonant with an optical transition can
produce large population imbalances among the magnetic sublevels of
atomic ground states as well as in excited states. The degree of this
radiatively-induced atomic level polarization, which is very sensitive
to the presence of magnetic fields, can be determined by observing the
intensity and polarization of the scattered or transmitted spectral
line radiation. Probably, the most important point for solar physics
is that the outer solar atmosphere is indeed an optically pumped vapor
and that the polarization of the emergent spectral line radiation
can be exploited for detecting magnetic fields that are too weak
and/or too tangled so as to produce measurable Zeeman polarization
signals. Here we present several radiative transfer simulations of the
linear polarization produced by optical pumping in selected FUV and
EUV lines of the solar atmosphere, showing that their sensitivity to
the Hanle effect is very suitable for magnetic field measurements in
the upper chromosphere and transition region of the Sun. These results
suggest that solar magnetometry using the spectral lines of optically
pumped atoms in the chromosphere, transition region and corona should
be a high-priority goal for large aperture solar telescopes, such as
ATST, EST and SOLAR-C.
---------------------------------------------------------
Title: The Lyα Lines of H I and He II: A Differential Hanle Effect
for Exploring the Magnetism of the Solar Transition Region
Authors: Trujillo Bueno, Javier; Štěpán, Jiří; Belluzzi, Luca
2012ApJ...746L...9T Altcode: 2011arXiv1112.4746T
The Lyα line of He II at 304 Å is one of the spectral lines
of choice for EUV channels of narrowband imagers on board space
telescopes, which provide spectacular intensity images of the outer
solar atmosphere. Since the magnetic field information is encoded in
the polarization of the spectral line radiation, it is important to
investigate whether the He II line radiation from the solar disk can
be polarized, along with its magnetic sensitivity. Here we report some
theoretical predictions concerning the linear polarization signals
produced by scattering processes in this strong emission line of
the solar transition region, taking into account radiative transfer
and the Hanle effect caused by the presence of organized and random
magnetic fields. We find that the fractional polarization amplitudes
are significant (~1%), even when considering the wavelength-integrated
signals. Interestingly, the scattering polarization of the Lyα line
of He II starts to be sensitive to the Hanle effect for magnetic
strengths B >~ 100 G (i.e., for magnetic strengths of the order of
and larger than the Hanle saturation field of the hydrogen Lyα line
at 1216 Å). We therefore propose simultaneous observations of the
scattering polarization in both Lyα lines to facilitate magnetic field
measurements in the upper solar chromosphere. Even the development
of a narrowband imaging polarimeter for the He II 304 Å line alone
would be already of great diagnostic value for probing the solar
transition region.
---------------------------------------------------------
Title: Ly-alpha polarimeter design for CLASP rocket experiment
Authors: Kubo, M.; Watanabe, H.; Narukage, N.; Ishikawa, R.; Bando,
T.; Kano, R.; Tsuneta, S.; Kobayashi, K.; Ichimoto, K.; Trujillo Bueno,
J.; Song, D.
2011AGUFM.P11F1627K Altcode:
A sounding-rocket program called the Chromospheric Lyman-Alpha
Spectro-Polarimeter (CLASP) is proposed to be launched in the Summer
of 2014. CLASP will observe the upper solar chromosphere in Ly-alpha
(121.567 nm), aiming to detect the linear polarization signal produced
by scattering processes and the Hanle effect for the first time. The
CLASP needs a rotating half-waveplate and a polarization analyzer
working at the Ly-alpha wavelength to measure the linear polarization
signal. We select Magnesium Fluoride (MgF2) as a material of the
optical components because of its birefringent property and high
transparency at UV wavelength. We have confirmed that the reflection
at the Brewster's Angle of MgF2 plate is a good polarization analyzer
for the Ly-alpha line by deriving its ordinary refractive index and
extinction coefficient along the ordinary and extraordinary axes. These
optical parameters are calculated with a least-square fitting in such a
way that the reflectance and transmittance satisfy the Kramers-Kronig
relation. The reflectance and transmittance against oblique incident
angles for the s-polarized and the p-polarized light are measured
using the synchrotron beamline at the Ultraviolet Synchrotron Orbital
Radiation Facility (UVSOR). We have also measured a retardation of
a zeroth-order waveplate made of MgF2. The thickness difference of
the waveplate is 14.57 um.This waveplate works as a half-waveplate at
121.74 nm. From this measurement, we estimate that a waveplate with
the thickness difference of 15.71 um will work as a half-waveplate
at the Ly-alpha wavelength. We have developed a rotating waveplate -
polarization analyzer system called a prototype of CLASP polarimeter,
and input the perfect Stokes Q and U signals. The modulation patterns
that are consistent with the theoretical prediction are successfully
obtained in both cases.
---------------------------------------------------------
Title: The Chromospheric Lyman-Alpha SpectroPolarimeter (CLASP)j
Authors: Kobayashi, K.; Tsuneta, S.; Trujillo Bueno, J.; Bando, T.;
Belluzzi, L.; Casini, R.; Carlsson, M.; Cirtain, J. W.; De Pontieu,
B.; Hara, H.; Ichimoto, K.; Ishikawa, R.; Kano, R.; Katsukawa, Y.;
Kim, T.; Kubo, M.; Manso Sainz, R.; Narukage, N.; Asensio Ramos,
A.; Robinson, B.; Sakao, T.; Shimizu, T.; Stepan, J.; Suematsu, Y.;
Watanabe, H.; West, E.; Winebarger, A. R.
2011AGUFM.P14C..05K Altcode:
We present an overview of the Chromospheric Lyman-Alpha
SpectroPolarimeter (CLASP) program. CLASP is a proposed sounding rocket
experiment currently under development as collaboration between Japan,
USA and Spain. The aim is to achieve the first measurement of magnetic
field in the upper chromosphere and transition region of the Sun
through the detection and measurement of Hanle effect polarization
of the Lyman alpha line. The Hanle effect (i.e. the magnetic field
induced modification of the linear polarization due to scattering
processes in spectral lines) is believed to be a powerful tool for
measuring the magnetic field in the upper chromosphere, as it is more
sensitive to weaker magnetic fields than the Zeeman effect, and also
sensitive to magnetic fields tangled at spatial scales too small to be
resolved. The Lyman-alpha (121.567 nm) line has been chosen because
it is a chromospheric/transition-region line, and because the Hanle
effect polarization of the Lyman-alpha line is predicted to be sensitive
to 10-250 Gauss, encompassing the range of interest. Hanle effect is
predicted to be observable as linear polarization or depolarization,
depending on the geometry, with a fractional polarization amplitude
varying between 0.1% and 1% depending on the strength and orientation of
the magnetic field. This quantification of the chromospheric magnetic
field requires a highly sensitive polarization measurement. The
CLASP instrument consists of a large aperture (287 mm) Cassegrain
telescope mated to a polarizing beamsplitter and a matched pair
of grating spectrographs. The polarizing beamsplitter consists
of a continuously rotating waveplate and a linear beamsplitter,
allowing simultaneous measurement of orthogonal polarizations and
in-flight self-calibration. Development of the instrument is underway,
and prototypes of all optical components have been tested using a
synchrotron beamline. The experiment is proposed for flight in 2014.
---------------------------------------------------------
Title: The Impact of Quantum Interference between Different J-levels
on Scattering Polarization in Spectral Lines
Authors: Belluzzi, Luca; Trujillo Bueno, Javier
2011ApJ...743....3B Altcode: 2011arXiv1109.0424B
The spectral line polarization produced by optically pumped atoms
contains a wealth of information on the thermal and magnetic structure
of a variety of astrophysical plasmas, including that of the solar
atmosphere. A correct decoding of such information from the observed
Stokes profiles requires a clear understanding of the effects that
radiatively induced quantum interference (or coherence) between pairs
of magnetic sublevels produces on these observables, in the absence of
and in the presence of magnetic fields of arbitrary strength. Here we
present a detailed theoretical investigation of the role of coherence
between pairs of sublevels pertaining to different fine-structure
J-levels, clarifying when it can be neglected for facilitating the
modeling of the linear polarization produced by scattering processes
in spectral lines. To this end, we apply the quantum theory of spectral
line polarization and calculate the linear polarization patterns of the
radiation scattered at 90° by a slab of stellar atmospheric plasma,
both taking into account and neglecting the above-mentioned quantum
interference. Particular attention is given to the <SUP>2</SUP> S -
<SUP>2</SUP> P, <SUP>5</SUP> S - <SUP>5</SUP> P, and <SUP>3</SUP> P -
<SUP>3</SUP> S multiplets. We point out the observational signatures
of this kind of interference and analyze its sensitivity to the energy
separation between the interfering levels, to the amount of emissivity
in the background continuum radiation, to lower-level polarization,
and to the presence of a magnetic field. Some interesting applications
to the following spectral lines are also presented: Ca II H and K,
Mg II h and k, Na I D<SUB>1</SUB> and D<SUB>2</SUB>, the Ba II 4554
Å and 4934 Å resonance lines, the Cr I triplet at 5207 Å, the O I
triplet at 7773 Å, the Mg I b-lines, and the Hα and Lyα lines of H I.
---------------------------------------------------------
Title: Scattering Polarization and Hanle Effect in Stellar Atmospheres
with Horizontal Inhomogeneities
Authors: Manso Sainz, Rafael; Trujillo Bueno, Javier
2011ApJ...743...12M Altcode: 2011arXiv1108.2958M
Scattering of light from an anisotropic source produces linear
polarization in spectral lines and in the continuum. In the outer
layers of a stellar atmosphere the anisotropy of the radiation field is
typically dominated by the radiation escaping away, but local horizontal
fluctuations of the physical conditions may also contribute, distorting
the illumination and, hence, the polarization pattern. Additionally,
a magnetic field may perturb and modify the line scattering polarization
signals through the Hanle effect. Here, we study such symmetry-breaking
effects. We develop a method to solve the transfer of polarized
radiation in a scattering atmosphere with weak horizontal fluctuations
of the opacity and source functions. It comprises linearization (small
opacity and Planck function fluctuations are assumed), reduction to
a quasi-plane-parallel problem through harmonic analysis, and the
problem's numerical solution by generalized standard techniques. We
apply this method to study scattering polarization in atmospheres with
horizontal fluctuations in the Planck function and opacity. We derive
several very general results and constraints from considerations on
the symmetries and dimensionality of the problem, and we give explicit
solutions of a few illustrative problems of special interest. For
example, we show (1) how the amplitudes of the fractional linear
polarization signals change when considering increasingly smaller
horizontal atmospheric inhomogeneities, (2) that in the presence of such
inhomogeneities even a vertical magnetic field may modify the scattering
line polarization, and (3) that forward scattering polarization may
be produced without the need for an inclined magnetic field. These
results are important for understanding the physics of the problem
and as benchmarks for multidimensional radiative transfer codes.
---------------------------------------------------------
Title: The Hanle Effect from Space for Measuring the Magnetic Fields
of the Upper Solar Chromosphere
Authors: Trujillo Bueno, J.; Stepan, J.; Belluzzi, L.; Manso Sainz, R.
2011AGUFM.P11F1626T Altcode:
We present some theoretical predictions concerning the amplitudes and
magnetic sensitivities of the linear polarization signals produced
by scattering processes in some UV and FUV spectral lines of the
upper chromosphere and transition region, such as Ly-alpha and Mg
II k. To this end, we have calculated the atomic level polarization
(population imbalances and quantum coherences) induced by anisotropic
radiation pumping in semi-empirical and hydrodynamical models of
the solar atmosphere, taking into account radiative transfer and the
Hanle effect caused by the presence of organized and random magnetic
fields. The amplitudes of the emergent linear polarization signals
are found to vary typically between a fraction of a percent and a few
percent, depending on the scattering geometry and the strength and
orientation of the magnetic field. The results shown here encourage the
development of UV polarimeters for sounding rockets and space telescopes
with the aim of opening up a true diagnostic window for magnetic field
measurements in the upper chromosphere and transition region of the Sun.
---------------------------------------------------------
Title: Ly-alpha polarimeter design for CLASP rocket experiment
Authors: Watanabe, H.; Narukage, N.; Kubo, M.; Ishikawa, R.; Bando, T.;
Kano, R.; Tsuneta, S.; Kobayashi, K.; Ichimoto, K.; Trujillo-Bueno, J.
2011SPIE.8148E..0TW Altcode: 2011SPIE.8148E..25W; 2014arXiv1407.4577W
A sounding-rocket program called the Chromospheric Lyman-Alpha
Spectro-Polarimeter (CLASP) is proposed to be launched in the summer of
2014. CLASP will observe the solar chromosphere in Ly-alpha (121.567
nm), aiming to detect the linear polarization signal produced by
scattering processes and the Hanle effect for the first time. The
polarimeter of CLASP consists of a rotating half-waveplate, a beam
splitter, and a polarization analyzer. Magnesium Fluoride (MgF2) is
used for these optical components, because MgF2 exhibits birefringent
property and high transparency at ultraviolet wavelength. The
development and comprehensive testing program of the optical components
of the polarimeter is underway using the synchrotron beamline at the
Ultraviolet Synchrotron Orbital Radiation Facility (UVSOR). The first
objective is deriving the optical constants of MgF2 by the measurement
of the reflectance and transmittance against oblique incident angles
for the s-polarized and the p-polarized light. The ordinary refractive
index and extinction coefficient along the ordinary and extraordinary
axes are derived with a least-square fitting in such a way that the
reflectance and transmittance satisfy the Kramers-Krönig relation. The
reflection at the Brewster's Angle of MgF2 plate is confirmed to become
a good polarization analyzer at Ly-alpha. The second objective is the
retardation measurement of a zeroth-order waveplate made of MgF2. The
retardation of a waveplate is determined by observing the modulation
amplitude that comes out of a waveplate and a polarization analyzer. We
tested a waveplate with the thickness difference of 14.57 um. The 14.57
um waveplate worked as a half-waveplate at 121.74 nm. We derived that
a waveplate with the thickness difference of 15.71 um will work as a
half-waveplate at Ly-alpha wavelength. We developed a prototype of CLASP
polarimeter using the MgF2 half-waveplate and polarization analyzers,
and succeeded in obtaining the modulation patterns that are consistent
with the theoretical prediction. We confirm that the performance of
the prototype is optimized for measuring linear polarization signal
with the least effect of the crosstalk from the circular polarization.
---------------------------------------------------------
Title: Overview of Chromospheric Lyman-Alpha SpectroPolarimeter
(CLASP)
Authors: Narukage, Noriyuki; Tsuneta, Saku; Bando, Takamasa; Kano,
Ryouhei; Kubo, Masahito; Ishikawa, Ryoko; Hara, Hirohisa; Suematsu,
Yoshinori; Katsukawa, Yukio; Watanabe, Hiroko; Ichimoto, Kiyoshi;
Sakao, Taro; Shimizu, Toshifumi; Kobayashi, Ken; Robinson, Brian; Kim,
Tony; Winebarger, Amy; West, Edward; Cirtain, Jonathan; De Pontieu,
Bart; Casini, Roberto; Trujillo Bueno, Javier; Stepan, Jiri; Manso
Sainz, Rafael; Belluzzi, Luca; Asensio Ramos, Andres; Carlsson, Mats
2011SPIE.8148E..0HN Altcode: 2011SPIE.8148E..16N
The solar chromosphere is an important boundary, through which all of
the plasma, magnetic fields and energy in the corona and solar wind
are supplied. Since the Zeeman splitting is typically smaller than
the Doppler line broadening in the chromosphere and transition region,
it is not effective to explore weak magnetic fields. However, this is
not the case for the Hanle effect, when we have an instrument with
high polarization sensitivity (~ 0.1%). "Chromospheric Lyman- Alpha
SpectroPolarimeter (CLASP)" is the sounding rocket experiment to detect
linear polarization produced by the Hanle effect in Lyman-alpha line
(121.567 nm) and to make the first direct measurement of magnetic
fields in the upper chromosphere and lower transition region. To
achieve the high sensitivity of ~ 0.1% within a rocket flight (5
minutes) in Lyman-alpha line, which is easily absorbed by materials,
we design the optical system mainly with reflections. The CLASP
consists of a classical Cassegrain telescope, a polarimeter and a
spectrometer. The polarimeter consists of a rotating 1/2-wave plate
and two reflecting polarization analyzers. One of the analyzer also
works as a polarization beam splitter to give us two orthogonal linear
polarizations simultaneously. The CLASP is planned to be launched in
2014 summer.
---------------------------------------------------------
Title: The Hanle Effect of the Hydrogen Lyα Line for Probing the
Magnetism of the Solar Transition Region
Authors: Trujillo Bueno, Javier; Štěpán, Jiří; Casini, Roberto
2011ApJ...738L..11T Altcode: 2011arXiv1107.4787T
We present some theoretical predictions concerning the amplitude and
magnetic sensitivity of the linear-polarization signals produced by
scattering processes in the hydrogen Lyα line of the solar transition
region. To this end, we have calculated the atomic-level polarization
(population imbalances and quantum coherences) induced by anisotropic
radiation pumping in semiempirical and hydrodynamical models of the
solar atmosphere, taking into account radiative transfer and the
Hanle effect caused by the presence of organized and random magnetic
fields. The line-center amplitudes of the emergent linear-polarization
signals are found to vary typically between 0.1% and 1%, depending
on the scattering geometry and the strength and orientation of the
magnetic field. The results shown here encourage the development of UV
polarimeters for sounding rockets and space telescopes with the aim
of opening up a diagnostic window for magnetic field measurements in
the upper chromosphere and transition region of the Sun.
---------------------------------------------------------
Title: HAZEL: HAnle and ZEeman Light
Authors: Asensio Ramos, Andrés; Trujillo Bueno, Javier; Landi
Degl'Innocenti, E.
2011ascl.soft09004A Altcode:
A big challenge in solar and stellar physics in the coming years
will be to decipher the magnetism of the solar outer atmosphere
(chromosphere and corona) along with its dynamic coupling with
the magnetic fields of the underlying photosphere. To this end, it
is important to develop rigorous diagnostic tools for the physical
interpretation of spectropolarimetric observations in suitably chosen
spectral lines. HAZEL is a computer program for the synthesis and
inversion of Stokes profiles caused by the joint action of atomic level
polarization and the Hanle and Zeeman effects in some spectral lines
of diagnostic interest, such as those of the He I 1083.0 nm and 587.6
nm (or D3) multiplets. It is based on the quantum theory of spectral
line polarization, which takes into account in a rigorous way all
the relevant physical mechanisms and ingredients (optical pumping,
atomic level polarization, level crossings and repulsions, Zeeman,
Paschen-Back and Hanle effects). The influence of radiative transfer
on the emergent spectral line radiation is taken into account through
a suitable slab model. The user can either calculate the emergent
intensity and polarization for any given magnetic field vector
or infer the dynamical and magnetic properties from the observed
Stokes profiles via an efficient inversion algorithm based on global
optimization methods.
---------------------------------------------------------
Title: Erratum: "Scattering Polarization of the Ca II
IR Triplet for Probing the Quiet Solar Chromosphere" <A
href="/abs/2010ApJ...722.1416M">(2010, ApJ, 722, 1416)</A>
Authors: Manso Sainz, R.; Trujillo Bueno, J.
2011ApJ...737..106M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Scattering Polarization of Hydrogen Lines in Weakly Magnetized
Stellar Atmospheres. I. Formulation and Application to Isothermal
Models
Authors: Štěpán, Jiří; Trujillo Bueno, Javier
2011ApJ...732...80S Altcode: 2011arXiv1102.4012S
Although the spectral lines of hydrogen contain valuable information
on the physical properties of a variety of astrophysical plasmas,
including the upper solar chromosphere, relatively little is known
about their scattering polarization signals, whose modification via the
Hanle effect may be exploited for magnetic field diagnostics. Here we
report on a basic theoretical investigation of the linear polarization
produced by scattering processes and the Hanle effect in Lyα, Lyβ,
and Hα taking into account multilevel radiative transfer effects
in an isothermal stellar atmosphere model, the fine-structure of the
hydrogen levels, as well as the impact of collisions with electrons
and protons. The main aim of this first paper is to elucidate the
key physical mechanisms that control the emergent fractional linear
polarization in the three lines, as well as its sensitivity to the
perturbers' density and to the strength and structure of microstructured
and deterministic magnetic fields. To this end, we apply an efficient
radiative transfer code we have developed for performing numerical
simulations of the Hanle effect in multilevel systems with overlapping
line transitions. For low-density plasmas, such as that of the upper
solar chromosphere, collisional depolarization is caused mainly by
collisional transitions between the fine-structure levels of the n =
3 level, so that it is virtually insignificant for Lyα but important
for Lyβ and Hα. We show the impact of the Hanle effect on the three
lines taking into account the radiative transfer coupling between
the different hydrogen line transitions. For example, we demonstrate
that the linear polarization profile of the Hα line is sensitive to
the presence of magnetic field gradients in the line core formation
region, and that in solar-like chromospheres selective absorption
of polarization components does not play any significant role in the
emergent scattering polarization.
---------------------------------------------------------
Title: Exploring the Magnetic Fields of Solar Prominences and Spicules
via He I D<SUB>3</SUB> Spectropolarimetry
Authors: Ramelli, R.; Trujillo Bueno, J.; Bianda, M.; Asensio Ramos, A.
2011ASPC..437..109R Altcode:
Over the last few years a large set of spectropolarimetric observations
of prominences and spicules in the He I D<SUB>3</SUB> multiplet have
been collected at the observatory of the <P />Istituto Ricerche Solari
Locarno (IRSOL), using increasingly improved versions of the ZIMPOL
polarimeter. The novel HAZEL inversion code of Stokes profiles generated
by the joint action of the Hanle and Zeeman effects is being applied
to this set of data, in order to infer the strength and geometry of
the magnetic field present in these structures. This paper presents
a brief overview of the most recent observations and inversions.
---------------------------------------------------------
Title: A Sounding Rocket Experiment for Spectropolarimetric
Observations with the Ly<SUB>α</SUB> Line at 121.6 nm (CLASP)
Authors: Ishikawa, R.; Bando, T.; Fujimura, D.; Hara, H.; Kano,
R.; Kobiki, T.; Narukage, N.; Tsuneta, S.; Ueda, K.; Wantanabe,
H.; Kobayashi, K.; Trujillo Bueno, J.; Manso Sainz, R.; Stepan, J.;
de Pontieu, B.; Carlsson, M.; Casini, R.
2011ASPC..437..287I Altcode:
A team consisting of Japan, USA, Spain, and Norway is developing a
high-throughput Chromospheric Lyman-Alpha SpectroPolarimeter (CLASP),
which is proposed to fly with a NASA sounding rocket in 2014. CLASP will
explore the magnetism of the upper solar chromosphere and transition
region via the Hanle effect of the Ly<SUB>α</SUB> line for the first
time. This experiment requires spectropolarimetric observations with
high polarimetric sensitivity (∼0.1%) and wavelength resolution
(0.1 Å). The final spatial resolution (slit width) is being discussed
taking into account the required high signal-to-noise ratio. We have
demonstrated the performance of the Ly<SUB>α</SUB> polarimeter by
extensively using the Ultraviolet Synchrotron ORbital Radiation Facility
(UVSOR) at the Institute for Molecular Sciences. In this contribution,
we report these measurements at UVSOR together with the current status
of the CLASP project.
---------------------------------------------------------
Title: Determining the Magnetization of the Quiet Sun Photosphere
from the Hanle Effect and Surface Dynamo Simulations
Authors: Shchukina, Nataliya; Trujillo Bueno, Javier
2011ApJ...731L..21S Altcode: 2011arXiv1103.5652S
The bulk of the quiet solar photosphere is thought to be significantly
magnetized, due to the ubiquitous presence of a tangled magnetic
field at subresolution scales with an average strength langBrang ~
100 G. This conclusion was reached through detailed three-dimensional
(3D) radiative transfer modeling of the Hanle effect in the Sr I 4607
Å line, using the microturbulent field approximation and assuming
that the shape of the probability density function of the magnetic
field strength is exponential. Here, we relax both approximations by
modeling the observed scattering polarization in terms of the Hanle
effect produced by the magnetic field of a 3D photospheric model
resulting from a (state-of-the-art) magneto-convection simulation
with surface dynamo action. We show that the scattering polarization
amplitudes observed in the Sr I 4607 Å line can be explained only
after enhancing the magnetic strength of the photospheric model by
a sizable scaling factor, F ≈ 10, which implies langBrang ≈ 130
G in the upper photosphere. We also argue that in order to explain
both the Hanle depolarization of the Sr I 4607 Å line and the Zeeman
signals observed in Fe I lines, we need to introduce a height-dependent
scaling factor, such that the ensuing langBrang ≈ 160 G in the low
photosphere and langBrang ≈ 130 G in the upper photosphere.
---------------------------------------------------------
Title: Modeling Scattering Polarization for Probing Solar Magnetism
Authors: Trujillo Bueno, J.
2011ASPC..437...83T Altcode: 2011arXiv1105.0323T
This paper considers the problem of modeling the light polarization that
emerges from an astrophysical plasma composed of atoms whose excitation
state is significantly influenced by the anisotropy of the incident
radiation field. In particular, it highlights how radiative transfer
simulations in three-dimensional models of the “quiet” solar
atmosphere may help us to probe its thermal and magnetic structure,
from the near equilibrium photosphere to the highly non-equilibrium
upper chromosphere. The paper finishes with predictions concerning the
amplitudes and magnetic sensitivities of the linear polarization signals
produced by scattering processes in two transition region lines, which
should encourage us to develop UV polarimeters for sounding rockets
and space telescopes with the aim of opening up a new diagnostic window
in astrophysics.
---------------------------------------------------------
Title: Scattering Polarization and the Hanle Effect in Hα as a
Probe of Chromospheric Magnetism: Modeling vs. Observations
Authors: Štěpán, J.; Trujillo Bueno, J.; Ramelli, R.; Bianda, M.
2011ASPC..437..117S Altcode: 2011arXiv1102.4941S
The Hanle effect in strong spectral lines is the physical mechanism
that should be increasingly exploited for quantitative explorations
of the magnetism of the quiet solar chromospheric plasma. Here we
show, by means of multilevel radiative transfer calculations and new
spectropolarimetric observations, that the amplitude and shape of the
scattering polarization profiles of the Hα line is very sensitive to
the strength and structure of the chromospheric magnetic field. The
interpretation of the observations in terms of one-dimensional radiative
transfer modeling suggests that there is an abrupt magnetization in
the upper chromosphere of the quiet Sun.
---------------------------------------------------------
Title: Solar Polarization Workshop 6
Authors: Kuhn, J. R.; Harrington, D. M.; Lin, H.; Berdyugina, S. V.;
Trujillo-Bueno, J.; Keil, S. L.; Rimmele, T.
2011ASPC..437.....K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Chromospheric Lyman Alpha SpectroPolarimeter (CLASP)
Authors: Kobayashi, K.; Tsuneta, S.; Trujillo Bueno, J.; Cirtain,
J. W.; Bando, T.; Kano, R.; Hara, H.; Fujimura, D.; Ueda, K.; Ishikawa,
R.; Watanabe, H.; Ichimoto, K.; Sakao, T.; de Pontieu, B.; Carlsson,
M.; Casini, R.
2010AGUFMSH11B1632K Altcode:
Magnetic fields in the solar chromosphere play a key role in the
energy transfer and dynamics of the solar atmosphere. Yet a direct
observation of the chromospheric magnetic field remains one of the
greatest challenges in solar physics. While some advances have been
made for observing the Zeeman effect in strong chromospheric lines,
the effect is small and difficult to detect outside sunspots. The
Hanle effect offers a promising alternative; it is sensitive to weaker
magnetic fields (e.g., 5-500 G for Ly-Alpha), and while its magnitude
saturates at stronger magnetic fields, the linear polarization signals
remain sensitive to the magnetic field orientation. The Hanle effect
is not only limited to off-limb observations. Because the chromosphere
is illuminated by an anisotropic radiation field, the Ly-Alpha line is
predicted to show linear polarization for on-disk, near-limb regions,
and magnetic field is predicted to cause a measurable depolarization. At
disk center, the Ly-Alpha radiation is predicted to be negligible
in the absence of magnetic field, and linearly polarized to an order
of 0.3% in the presence of an inclined magnetic field. The proposed
CLASP sounding rocket instrument is designed to detect 0.3% linear
polarization of the Ly-Alpha line at 1.5 arcsecond spatial resolution
(0.7’’ pixel size) and 10 pm spectral resolution. The instrument
consists of a 30 cm aperture Cassegrain telescope and a dual-beam
spectropolarimeter. The telescope employs a “cold mirror’’ design
that uses multilayer coatings to reflect only the target wavelength
range into the spectropolarimeter. The polarization analyzer consists of
a rotating waveplate and a polarizing beamsplitter that comprises MgF2
plates placed at Brewster’s Angle. Each output beam of the polarizing
beamsplitter, representing two orthogonal linear polarizations, is
dispersed and focused using a separate spherical varied-line-space
grating, and imaged with a separate 512x512 CCD camera. Prototypes
of key optical components have been fabricated and tested. Instrument
design is being finalized, and the experiment will be proposed for a
2014 flight aboard a NASA sounding rocket.
---------------------------------------------------------
Title: On the Sensitivity of Partial Redistribution Scattering
Polarization Profiles to Various Atmospheric Parameters
Authors: Sampoorna, M.; Trujillo Bueno, J.; Landi Degl'Innocenti, E.
2010ApJ...722.1269S Altcode: 2010arXiv1008.2585S
This paper presents a detailed study of the scattering polarization
profiles formed under partial frequency redistribution (PRD) in two
thermal models of the solar atmosphere. Particular attention is given
to understanding the influence of several atmospheric parameters on the
emergent fractional linear polarization profiles. The shapes of these
Q/I profiles are interpreted in terms of the anisotropy of the radiation
field, which in turn depends on the source function gradient that sets
the angular variation of the specific intensity. We define a suitable
frequency integrated anisotropy factor for PRD that can be directly
related to the emergent linear polarization. We show that complete
frequency redistribution is a good approximation to model weak resonance
lines. We also show that the emergent linear polarization profiles can
be very sensitive to the thermal structure of the solar atmosphere and,
in particular, to spatial variations of the damping parameter.
---------------------------------------------------------
Title: Scattering Polarization of the Ca II IR Triplet for Probing
the Quiet Solar Chromosphere
Authors: Manso Sainz, R.; Trujillo Bueno, J.
2010ApJ...722.1416M Altcode: 2010arXiv1007.0727M
The chromosphere of the quiet Sun is a very important stellar
atmospheric region whose thermal and magnetic structure we need to
decipher in order to unlock new discoveries in solar and stellar
physics. To this end, we need to identify and exploit observables
sensitive to weak magnetic fields (B <~ 100 G) and to the presence
of cool and hot gas in the bulk of the solar chromosphere. Here, we
report on an investigation of the Hanle effect in two semi-empirical
models of the quiet solar atmosphere with different chromospheric
thermal structures. Our study reveals that the linear polarization
profiles produced by scattering in the Ca II IR triplet have thermal
and magnetic sensitivities potentially of great diagnostic value. The
linear polarization in the 8498 Å line shows a strong sensitivity to
inclined magnetic fields with strengths between 0.001 and 10 G, while
the emergent linear polarization in the 8542 Å and 8662 Å lines is
mainly sensitive to magnetic fields with strengths between 0.001 and 0.1
G. The reason for this is that the scattering polarization of the 8542
Å and 8662 Å lines, unlike the 8498 Å line, is controlled mainly
by the Hanle effect in their (metastable) lower levels. Therefore,
in regions with magnetic strengths noticeably larger than 1 G, their
Stokes Q and U profiles are sensitive only to the orientation of the
magnetic field vector. We also find that for given magnetic field
configurations the sign of the Q/I and U/I profiles of the 8542 Å and
8662 Å lines is the same in both atmospheric models, while the sign
of the linear polarization profile of the 8498 Å line turns out to be
very sensitive to the thermal structure of the lower chromosphere. We
suggest that spectropolarimetric observations providing information
on the relative scattering polarization amplitudes of the Ca II IR
triplet will be very useful to improve our empirical understanding of
the thermal and magnetic structure of the quiet chromosphere.
---------------------------------------------------------
Title: Gauss-Seidel and Successive Overrelaxation Methods for
Radiative Transfer with Partial Frequency Redistribution
Authors: Sampoorna, M.; Trujillo Bueno, J.
2010ApJ...712.1331S Altcode: 2010arXiv1002.4179S
The linearly polarized solar limb spectrum that is produced by
scattering processes contains a wealth of information on the physical
conditions and magnetic fields of the solar outer atmosphere, but the
modeling of many of its strongest spectral lines requires solving
an involved non-local thermodynamic equilibrium radiative transfer
problem accounting for partial redistribution (PRD) effects. Fast
radiative transfer methods for the numerical solution of PRD problems
are also needed for a proper treatment of hydrogen lines when aiming at
realistic time-dependent magnetohydrodynamic simulations of the solar
chromosphere. Here we show how the two-level atom PRD problem with
and without polarization can be solved accurately and efficiently
via the application of highly convergent iterative schemes based
on the Gauss-Seidel and successive overrelaxation (SOR) radiative
transfer methods that had been previously developed for the complete
redistribution case. Of particular interest is the Symmetric SOR method,
which allows us to reach the fully converged solution with an order of
magnitude of improvement in the total computational time with respect
to the Jacobi-based local accelerated lambda iteration method.
---------------------------------------------------------
Title: On the Probable Existence of an Abrupt Magnetization in the
Upper Chromosphere of the Quiet Sun
Authors: Štěpán, Jiří; Trujillo Bueno, Javier
2010ApJ...711L.133S Altcode: 2010arXiv1002.1574S
We report on a detailed radiative transfer modeling of the observed
scattering polarization in the Hα line, which allows us to infer
quantitative information on the magnetization of the quiet solar
chromosphere. Our analysis suggests the presence of a magnetic
complexity zone with a mean field strength langBrang > 30 G lying
just below the sudden transition region to the coronal temperatures. The
chromospheric plasma directly underneath is very weakly magnetized,
with langBrang ~ 1 G. The possible existence of this abrupt change in
the degree of magnetization of the upper chromosphere of the quiet Sun
might have large significance for our understanding of chromospheric
(and, therefore, coronal) heating.
---------------------------------------------------------
Title: On the 3D structure of the magnetic field in regions of
emerging flux .
Authors: Asensio Ramos, A.; Trujillo Bueno, J.
2010MmSAI..81..625A Altcode: 2010arXiv1001.2108A
We explore the photospheric and chromospheric magnetic field in an
emerging flux region. An image of the equivalent width of the He I
10830 Å red blended component shows the presence of filamentary
structures that might be interpreted as magnetic loops. We point
out that the magnetic field strength in the chromosphere resembles a
smoothed version of that found in the photosphere and that it is not
correlated at all with the above-mentioned equivalent width map. Lacking
other diagnostics, this suggests that one cannot discard the possibility
that the chromospheric field we infer from the observations is tracing
the lower chromosphere of the active region instead of tracing the
magnetic field along loops. If the He I line is formed within magnetic
loops, we point out a potential problem that appears when interpreting
observations using only one component along the line-of-sight.
---------------------------------------------------------
Title: On the sensitivity of the Halpha scattering polarization to
chromospheric magnetism
Authors: Štěpán, Jiří; Trujillo Bueno, Javier
2010MmSAI..81..810S Altcode: 2010arXiv1001.2720S
A particularly interesting line for exploring the physical conditions
of the quiet solar chromosphere is Halpha , but its intensity profile
is magnetically insensitive and the small circular polarization
signatures produced by the longitudinal Zeeman effect come mainly
from the underlying photosphere. Here we show that the Hanle effect in
Halpha provides quantitative information on the magnetism of the quiet
chromosphere. To this end, we calculate the response function of the
emergent scattering polarization to perturbations in the magnetic field.
---------------------------------------------------------
Title: On the Magnetic Field of Off-limb Spicules
Authors: Centeno, Rebecca; Trujillo Bueno, Javier; Asensio Ramos,
Andrés
2010ApJ...708.1579C Altcode: 2009arXiv0911.3149C
Determining the magnetic field related to solar spicules is vital for
developing adequate models of these plasma jets, which are thought to
play a key role in the thermal, dynamic, and magnetic structure of the
chromosphere. Here we report on the magnetic properties of off-limb
spicules in a very quiet region of the solar atmosphere, as inferred
from new spectropolarimetric observations in the He I 10830 Å triplet
obtained with the Tenerife Infrared Polarimeter. We have used a novel
inversion code for Stokes profiles caused by the joint action of atomic
level polarization and the Hanle and Zeeman effects to interpret the
observations (HAZEL, from HAnle and ZEeman Light). Magnetic fields as
strong as ~50 G were detected in a very localized area of the slit,
which could represent a possible lower value of the field strength of
organized network spicules.
---------------------------------------------------------
Title: The Magnetic Field of Solar Spicules
Authors: Centeno, R.; Trujillo Bueno, J.; Asensio Ramos, A.
2010ASSP...19..255C Altcode: 2010mcia.conf..255C; 2009arXiv0903.0002C
Determining the magnetic field of solar spicules is vital for
developing adequate models of these plasma jets, which are thought to
play a key role in the thermal, dynamic, and magnetic structure of the
chromosphere. Here we report on magnetic spicule properties in a very
quiet region of the off-limb solar atmosphere, as inferred from new
spectropolarimetric observations in the He I 10830Å triplet. We have
used a novel inversion code for Stokes profiles caused by the joint
action of atomic level polarization and the Hanle and Zeeman effects
(HAZEL) to interpret the observations. Magnetic fields as strong as
40G were unambiguously detected in a very localized area of the slit,
which may represent a possible lower value of the field strength of
organized network spicules.
---------------------------------------------------------
Title: Recent Advances in Chromospheric and Coronal Polarization
Diagnostics
Authors: Trujillo Bueno, J.
2010ASSP...19..118T Altcode: 2010mcia.conf..118T; 2009arXiv0903.4372T; 2010ASSP...19..118B
I review some recent advances in methods to diagnose polarized
radiation with which we may hope to explore the magnetism of the solar
chromosphere and corona. These methods are based on the remarkable
signatures that the radiatively induced quantum coherences produce
in the emergent spectral line polarization and on the joint action
of the Hanle and Zeeman effects. Some applications to spicules,
prominences, active region filaments, emerging flux regions, and the
quiet chromosphere are discussed.
---------------------------------------------------------
Title: Spectropolarimetric investigations of the magnetization of
the quiet-Sun chromosphere .
Authors: Trujillo Bueno, J.
2010MmSAI..81..681T Altcode: 2010arXiv1002.2615T
This paper reviews some recent advances in the development and
application of polarized radiation diagnostics to infer the mean
magnetization of the quiet solar atmosphere, from the near equilibrium
photosphere to the highly non-equilibrium upper chromosphere. In
particular, I show that interpretations of the scattering polarization
observed in some spectral lines suggest that while the magnetization
of the photosphere and upper chromosphere is very significant, the
lower chromosphere seems to be weakly magnetized.
---------------------------------------------------------
Title: Two Suggestions to See the Hidden Magnetism of the Solar
Chromosphere
Authors: Trujillo Bueno, J.
2009ASPC..415..121T Altcode: 2009arXiv0909.4463T
Solar magnetic fields leave their fingerprints in the polarization
signatures of the emergent spectral line radiation. This occurs through
a variety of rather unfamiliar physical mechanisms, not only via
the Zeeman effect. In particular, magnetic fields modify the atomic
level polarization (population imbalances and quantum coherences)
that anisotropic radiative pumping processes induce in the atoms and
molecules of the solar atmosphere. Interestingly, this so-called Hanle
effect allows us to “see” magnetic fields to which the Zeeman effect
is blind within the limitations of the available instrumentation. Here
I argue that the Ca II IR triplet and the He I 10830 Å multiplet would
be very suitable choices for investigating the magnetism of the solar
chromosphere via spectropolarimetric observations from a future space
telescope, such as JAXA's SOLAR-C mission.
---------------------------------------------------------
Title: The Physical Origin and the Diagnostic Potential of the
Scattering Polarization in the Li I Resonance Doublet at 6708 Å
Authors: Belluzzi, Luca; Landi Degl'Innocenti, Egidio; Trujillo
Bueno, Javier
2009ApJ...705..218B Altcode: 2009arXiv0909.3748B
High-sensitivity measurements of the linearly polarized solar limb
spectrum produced by scattering processes in quiet regions of the solar
atmosphere showed that the Q/I profile of the lithium doublet at 6708 Å
has an amplitude ~10<SUP>-4</SUP> and a curious three-peak structure,
qualitatively similar to that found and confirmed by many observers in
the Na I D<SUB>2</SUB> line. Given that a precise measurement of the
scattering polarization profile of the lithium doublet lies at the
limit of the present observational possibilities, it is worthwhile
to clarify the physical origin of the observed polarization, its
diagnostic potential, and what kind of Q/I shapes can be expected from
theory. To this end, we have applied the quantum theory of atomic
level polarization taking into account the hyperfine structure of
the two stable isotopes of lithium, as well as the Hanle effect
of a microturbulent magnetic field of arbitrary strength. We find
that quantum interferences between the sublevels pertaining to the
upper levels of the D<SUB>2</SUB> and D<SUB>1</SUB> line transitions
of lithium do not cause any observable effect on the emergent Q/I
profile. Our theoretical calculations show that only two Q/I peaks
can be expected, with the strongest one caused by the D<SUB>2</SUB>
line of <SUP>7</SUP>Li I and the weakest one due to the D<SUB>2</SUB>
line of <SUP>6</SUP>Li I. Interestingly, we find that these two peaks
in the theoretical Q/I profile stand out clearly only when the kinetic
temperature of the thin atmospheric region that produces the emergent
spectral line radiation is lower than 4000 K. The fact that such a thin
atmospheric region is located around a height of 200 km in standard
semi-empirical models, where the kinetic temperature is about 5000 K,
leads us to suggest that the most likely Q/I profile produced by the
Sun in the lithium doublet should be slightly asymmetric and dominated
by the <SUP>7</SUP>Li I peak.
---------------------------------------------------------
Title: The Second Stellar Spectrum and the non-LTE Problem of the
2nd Kind
Authors: Trujillo Bueno, Javier
2009AIPC.1171...27T Altcode: 2009AIPC.1171...27B; 2009arXiv0911.4669T
This paper presents an overview of the radiative transfer problem
of calculating the spectral line intensity and polarization that
emerges from a (generally magnetized) astrophysical plasma composed
of atoms and molecules whose excitation state is significantly
influenced by radiative transitions produced by an anisotropic
radiation field. The numerical solution of this non-LTE problem
of the 2nd kind is facilitating the physical understanding of the
second solar spectrum and the exploration of the complex magnetism
of the extended solar atmosphere, but much more could be learned if
high-sensitivity polarimeters were developed also for the present
generation of night-time telescopes. Interestingly, I find that the
population ratio between the levels of some resonance line transitions
can be efficiently modulated by the inclination of a weak magnetic
field when the anisotropy of the incident radiation is significant,
something that could provide a new diagnostic tool in astrophysics.
---------------------------------------------------------
Title: The Sensitivity of the Second Solar Spectrum of the Li I 6708
Å Doublet to the Lithium Isotopic Abundance and to a Microturbulent
Magnetic Field
Authors: Belluzzi, L.; Landi Degl'Innocenti, E.; Trujillo Bueno, J.
2009ASPC..405..107B Altcode:
The second solar spectrum offers a novel diagnostic window not only to
explore the magnetic field of our nearest star, but also to determine
the atomic and isotopic abundances in the solar atmosphere. A very
interesting example, concerning this second aspect, is the Li I
resonance doublet at 6708~Å. Here we present a detailed theoretical
investigation, carried out within the framework of the density matrix
formalism, on the atomic physics that is involved in the generation
of the observed Q/I profile, which is the result of a complex blend
of the D_1 and D_2 lines of the two stable isotopes of lithium (^6Li
and ^7Li), both showing hyperfine structure. We discuss the diagnostic
potential of this linear polarization profile for the determination of
the lithium isotopic abundance in the quiet Sun, and we investigate the
magnetic sensitivity of this profile to a microturbulent magnetic field.
---------------------------------------------------------
Title: Three-dimensional Radiative Transfer Modeling of the Second
Solar Spectrum of Titanium
Authors: Shchukina, N. G.; Trujillo Bueno, J. T.
2009ASPC..405..275S Altcode:
Here we present multilevel radiative transfer calculations of the
scattering polarization of neutral titanium lines in a three-dimensional
model of the solar photosphere, which we have obtained from realistic
hydrodynamical simulations of solar surface convection. We consider
the particularly interesting case of the Ti I multiplet a{^5}F -
y{^5}F<SUP>o</SUP>, which is well suited for investigating the Sun's
hidden magnetism via the differential Hanle effect. After considering
the unmagnetized reference case, we show that the depolarization
produced by a volume-filling microturbulent field with a strength such
that it produces saturation of the upper-level Hanle effect leads to
a much better fit to Gandorfer's (2002) observations.
---------------------------------------------------------
Title: The Magnetic Sensitivity of the Second Solar Spectrum
Authors: Trujillo Bueno, J.
2009ASPC..405...65T Altcode: 2008arXiv0812.4400T
This paper reviews some of the developments that over the last 10
years have allowed us to go from deciphering the physical origin
of several of the enigmatic features of the second solar spectrum
to discovering unknown aspects of the Sun's hidden magnetism via
sophisticated radiative transfer modeling. The second solar spectrum is
the observational signature of radiatively induced quantum coherences
in the atoms and molecules of the solar atmosphere. Magnetic
fields produce partial decoherence via the Hanle effect, giving
rise to fascinating observable effects in the emergent spectral
line polarization. Interestingly, these effects allow us to “see"
magnetic fields to which the Zeeman effect is blind within the
limitations of the available instrumentation. In the coming years,
the physical interpretation of observations of the spectral line
polarization resulting from the joint action of the Hanle and Zeeman
effects might lead to a new revolution in our empirical understanding
of solar magnetic fields.
---------------------------------------------------------
Title: Synthesis and Inversion of He I Stokes Profiles Caused by
the Joint Action of the Hanle and Zeeman Effects
Authors: Asensio Ramos, A.; Trujillo Bueno, J.
2009ASPC..405..281A Altcode: 2009ASPC..405..281R
We have developed a robust but user-friendly computer program for the
synthesis and inversion of Stokes profiles caused by the joint action
of the Hanle and Zeeman effects in some spectral lines of diagnostic
interest. The influence of radiative transfer on the emergent spectral
line radiation is taken into account through a suitable slab model. The
dynamical and magnetic properties of the observed plasma structure are
inferred from the observed Stokes profiles via an efficient inversion
algorithm based on global optimization methods. Here we introduce
it briefly to the solar and stellar physics community by showing the
first results of an application to the He I 10830 Å multiplet, whose
aim is to obtain empirical information on the strength and orientation
of the magnetic field vector in an internetwork region of the solar
chromosphere.
---------------------------------------------------------
Title: Flux Cancellation in the Solar Photosphere: a near-IR Line
of Mn I as a Diagnostic Tool
Authors: Asensio Ramos, A.; Martínez González, M. J.; López Ariste,
A.; Trujillo Bueno, J.; Collados, M.
2009ASPC..405..215A Altcode:
Recently, \cite{asensio_2_asensio_mn07} pointed out that the near-IR
line of Mn I at 15262.702 Å provides a new diagnostic window for
exploring the magnetism of the quiet Sun. In contrast with previously
considered Mn I lines located at visible wavelengths this near-IR
line has the advantage that the shape of its intensity profile is very
sensitive to the presence of magnetic fields. This enhanced magnetic
sensitivity is produced by the coincidence of two favorable facts:
the enhanced Zeeman sensitivity of near-IR lines and because this line
is subjected to particularly strong Paschen-Back perturbations due to
the hyperfine structure of manganese. Of great diagnostic interest is
that the intensity profile itself give us information on the unsigned
magnetic flux, while the polarization profiles are sensitive to the
net flux. An application to spectropolarimetric observations with the
Tenerife Infrared Polarimeter has allowed us to obtain the first flux
cancellation map in an enhanced network region.
---------------------------------------------------------
Title: A Possible Polarization Mechanism of EUV Coronal Lines
Authors: Manso Sainz, R.; Trujillo Bueno, J.
2009ASPC..405..423M Altcode:
The alignment generated in the ground level of Fe X by scattering
in the coronal red line λ6374, can be efficiently transferred by
collisions to upper levels; the ensuing spontaneous emission in
allowed EUV transitions (as 174.5~Å and 177~Å) is then linearly
polarized. The polarization thus generated would be sensitive to
the electronic density (N<SUB>e</SUB>) and to the magnetic field
orientation although not to the field strength. At N<SUB>e</SUB>∼
10^7~cm<SUP>-3</SUP> the linear polarization would be ∼1% just
over the solar surface and ∼5% at 0.2R_⊙, rapidly decaying for
N<SUB>e</SUB>> 10^8~cm<SUP>-3</SUP>. The mechanism works for other
spectral lines and ions too.
---------------------------------------------------------
Title: Observations of the Joint Action of the Hanle and Zeeman
Effects in the D_2 Line of Ba II
Authors: Ramelli, R.; Bianda, M.; Trujillo Bueno, J.; Belluzzi, L.;
Landi Degl'Innocenti, E.
2009ASPC..405...41R Altcode: 2009arXiv0906.2320R
We show a selection of high-sensitivity spectropolarimetric observations
obtained over the last few years in the Ba II D_2-line with the Zürich
Imaging Polarimeter (ZIMPOL) attached to the Gregory Coudé Telescope
of IRSOL. The measurements were collected close to the solar limb, in
several regions with varying degree of magnetic activity. The Stokes
profiles we have observed show clear signatures of the joint action
of the Hanle and Zeeman effects, in very good qualitative agreement
with the theoretical expectations. Polarimetric measurements of this
line show to be very well suited for magnetic field diagnostics of
the lower solar chromosphere, from regions with field intensities as
low as 1 gauss to strongly magnetized ones having kG field strengths.
---------------------------------------------------------
Title: Influence of Coronal EUV Irradiance on the Stokes Profiles
of the He I 10830 Å Multiplet
Authors: Centeno, R.; Trujillo Bueno, J.; Uitenbroek, H.; Collados, M.
2009ASPC..405..297C Altcode:
One of the most useful spectral windows for spectropolarimetric
investigations of the solar chromosphere is the one provided by the
spectral lines of the He I 10830 Å multiplet, whose polarization
signals are sensitive to the Hanle and Zeeman effects. However, in
order to be able to carry out reliable diagnostics of the dynamic
and magnetic properties of the solar outer atmosphere it is crucial
to have a good physical understanding of the sensitivity of the
observed spectral line radiation to the various competing triggering
mechanisms. Here we report a series of on-disk and off-the-limb
non-LTE calculations of the 10830 Å absorption and emission profiles,
focusing our investigation on their sensitivity to the EUV coronal
irradiation and the model atmosphere used in the calculations. We show
in what respects the on-disk case sensitivity of the polarization
signals induced by the Zeeman effect to the EUV coronal irradiance,
and investigate whether or not inversions based on the Milne-Eddington
model are reliable. Concerning the off-the-limb case we demonstrate
that the intensity ratio of the blue to the red components of the
He I 10830 Å multiplet is a sensitive function of the amount of EUV
coronal illumination. Therefore, measurements of this observable as
a function of the distance to the limb and its confrontation with
radiative transfer modeling might give us valuable information on the
physical properties of the solar atmosphere and on the amount of EUV
radiation penetrating the chromosphere from above.
---------------------------------------------------------
Title: Three-dimensional Radiative Transfer Modeling of the
Polarization of the Sun's Continuous Spectrum
Authors: Trujillo Bueno, Javier; Shchukina, Nataliya
2009ApJ...694.1364T Altcode: 2008arXiv0812.3494T; 2009ApJ...694.1364B
Polarized light provides the most reliable source of information at
our disposal for diagnosing the physical properties of astrophysical
plasmas, including the three-dimensional (3D) structure of the solar
atmosphere. Here we formulate and solve the 3D radiative transfer
problem of the linear polarization of the solar continuous radiation,
which is principally produced by Rayleigh and Thomson scattering. Our
approach takes into account not only the anisotropy of the solar
continuum radiation but also the symmetry-breaking effects caused
by the horizontal atmospheric inhomogeneities produced by the solar
surface convection. We show that such symmetry-breaking effects do
produce observable signatures in Q/I and U/I, even at the very center
of the solar disk where we observe the forward scattering case, but
their detection would require obtaining very high resolution linear
polarization images of the solar surface. Without spatial and/or
temporal resolution U/I ≈ 0 and the only observable quantity is
Q/I, whose wavelength variation at a solar disk position close to the
limb has been recently determined semi-empirically. Interestingly,
our 3D radiative transfer modeling of the polarization of the Sun's
continuous spectrum in a well-known 3D hydrodynamical model of the
solar photosphere shows remarkable agreement with the semi-empirical
determination, significantly better than that obtained via the use of
one-dimensional (1D) atmospheric models. Although this result confirms
that the above-mentioned 3D model was indeed a suitable choice for
our Hanle-effect estimation of the substantial amount of "hidden"
magnetic energy that is stored in the quiet solar photosphere,
we have found however some small discrepancies whose origin may
be due to uncertainties in the semi-empirical data and/or in the
thermal and density structure of the 3D model. For this reason, we
have paid some attention also to other (more familiar) observables,
like the center-limb variation of the continuum intensity, which we
have calculated taking into account the scattering contribution to
the continuum source function. The overall agreement with the observed
center-limb variation turns out to be impressive, but we find a hint
that the model's temperature gradients in the continuum-forming layers
could be slightly too steep, perhaps because all current simulations of
solar surface convection and magnetoconvection compute the radiative
flux divergence ignoring the fact that the effective polarizability
is not completely negligible, especially in the downward-moving
intergranular lane plasma.
---------------------------------------------------------
Title: Diagnostic methods based on scattering polarization and the
joint action of the Hanle and Zeeman effects
Authors: Trujillo Bueno, Javier
2009IAUS..259..623T Altcode:
Polarized light provides the most reliable source of information at
our disposal for diagnosing the physical properties of astrophysical
plasmas, including the magnetic fields of the solar atmosphere. The
interaction between radiation and hydrogen plus free electrons through
Rayleigh and Thomson scattering gives rise to the polarization of the
stellar continuous spectrum, which is very sensitive to the medium's
thermal and density structure. Anisotropic radiative pumping processes
induce population imbalances and quantum coherences among the sublevels
of degenerate energy levels (that is, atomic level polarization),
which produce polarization in spectral lines without the need of a
magnetic field. The Hanle effect caused by the presence of relatively
weak magnetic fields modifies the atomic polarization of the upper and
lower levels of the spectral lines under consideration, allowing us
to detect magnetic fields to which the Zeeman effect is blind. After
discussing the physical origin of the polarized radiation in stellar
atmospheres, this paper highlights some recent developments in polarized
radiation diagnostic methods and a few examples of their application
in solar physics.
---------------------------------------------------------
Title: Wave Propagation and Shock Formation in Different Magnetic
Structures
Authors: Centeno, R.; Collados, M.; Trujillo Bueno, J.
2009ApJ...692.1211C Altcode: 2008arXiv0810.3613C
Velocity oscillations "measured" simultaneously at the photosphere and
the chromosphere—from time series of spectropolarimetric data in the
10830 Å region—of different solar magnetic features allow us to study
the properties of wave propagation as a function of the magnetic flux
of the structure (i.e., two different-sized sunspots, a tiny pore,
and a facular region). While photospheric oscillations have similar
characteristics everywhere, oscillations measured at chromospheric
heights show different amplitudes, frequencies, and stages of shock
development depending on the observed magnetic feature. The analysis
of the power and the phase spectra, together with simple theoretical
modeling, lead to a series of results concerning wave propagation
within the range of heights of this study. We find that, while the
atmospheric cutoff frequency and the propagation properties of different
oscillating modes depend on the magnetic feature, in all the cases the
power that reaches the high chromosphere above the atmospheric cutoff
comes directly from the photosphere by means of linear vertical wave
propagation rather than from nonlinear interaction of modes.
---------------------------------------------------------
Title: Advanced Forward Modeling and Inversion of Stokes Profiles
Resulting from the Joint Action of the Hanle and Zeeman Effects
Authors: Asensio Ramos, A.; Trujillo Bueno, J.; Landi Degl'Innocenti,
E.
2008ApJ...683..542A Altcode: 2008arXiv0804.2695A
A big challenge in solar and stellar physics in the coming years
will be to decipher the magnetism of the solar outer atmosphere
(chromosphere and corona) along with its dynamic coupling with
the magnetic fields of the underlying photosphere. To this end, it
is important to develop rigorous diagnostic tools for the physical
interpretation of spectropolarimetric observations in suitably chosen
spectral lines. Here we present a computer program for the synthesis and
inversion of Stokes profiles caused by the joint action of atomic level
polarization and the Hanle and Zeeman effects in some spectral lines
of diagnostic interest, such as those of the He I 10830 Å and 5876 Å
(or D<SUB>3</SUB>) multiplets. It is based on the quantum theory of
spectral line polarization, which takes into account in a rigorous way
all the relevant physical mechanisms and ingredients (optical pumping,
atomic level polarization, level crossings and repulsions, Zeeman,
Paschen-Back, and Hanle effects). The influence of radiative transfer
on the emergent spectral line radiation is taken into account through
a suitable slab model. The user can either calculate the emergent
intensity and polarization for any given magnetic field vector or infer
the dynamical and magnetic properties from the observed Stokes profiles
via an efficient inversion algorithm based on global optimization
methods. The reliability of the forward modeling and inversion code
presented here is demonstrated through several applications, which range
from the inference of the magnetic field vector in solar active regions
to determining whether or not it is canopy-like in quiet chromospheric
regions. This user-friendly diagnostic tool called "HAZEL" (from HAnle
and ZEeman Light) is offered to the astrophysical community, with the
hope that it will facilitate new advances in solar and stellar physics.
---------------------------------------------------------
Title: The Influence of Coronal EUV Irradiance on the Emission in
the He I 10830 Å and D<SUB>3</SUB> Multiplets
Authors: Centeno, R.; Trujillo Bueno, J.; Uitenbroek, H.; Collados, M.
2008ApJ...677..742C Altcode: 2007arXiv0712.2203C
Two of the most attractive spectral windows for spectropolarimetric
investigations of the physical properties of the plasma structures
in the solar chromosphere and corona are the ones provided by the
spectral lines of the He I 10830 and 5876 Å (or D<SUB>3</SUB>)
multiplets, whose polarization signals are sensitive to the Hanle and
Zeeman effects. However, in order to be able to carry out reliable
diagnostics, it is crucial to have a good physical understanding
of the sensitivity of the observed spectral line radiation to the
various competing driving mechanisms. Here we report a series of
off-the-limb non-LTE calculations of the He I D<SUB>3</SUB> and 10830
Å emission profiles, focusing our investigation on their sensitivity
to the EUV coronal irradiation and the model atmosphere used in the
calculations. We show in particular that the intensity ratio of the
blue to the red components in the emission profiles of the He I 10830
Å multiplet turns out to be a good candidate as a diagnostic tool for
the coronal irradiance. Measurements of this observable as a function of
the distance to the limb and its confrontation with radiative transfer
modeling might give us valuable information on the physical properties
of the solar atmosphere and on the amount of EUV radiation at relevant
wavelengths penetrating the chromosphere from above.
---------------------------------------------------------
Title: Channeling 5 Minute Photospheric Oscillations into the Solar
Outer Atmosphere through Small-Scale Vertical Magnetic Flux Tubes
Authors: Khomenko, E.; Centeno, R.; Collados, M.; Trujillo Bueno, J.
2008ApJ...676L..85K Altcode: 2008arXiv0802.0938K
We report two-dimensional MHD simulations which demonstrate that
photospheric 5 minute oscillations can leak into the chromosphere
inside small-scale vertical magnetic flux tubes. The results of
our numerical experiments are compatible with those inferred from
simultaneous spectropolarimetric observations of the photosphere and
chromosphere obtained with the Tenerife Infrared Polarimeter (TIP)
at 10830 Å. We conclude that the efficiency of energy exchange by
radiation in the solar photosphere can lead to a significant reduction
of the cutoff frequency and may allow for the propagation of the 5
minute waves vertically into the chromosphere.
---------------------------------------------------------
Title: Three-dimensional Radiative Transfer with Multilevel Atoms
Authors: Fabiani Bendicho, P.; Trujillo Bueno, J.
2007arXiv0710.5427F Altcode:
The efficient numerical solution of Non-LTE multilevel transfer problems
requires the combination of highly convergent iterative schemes with
fast and accurate formal solution methods of the radiative transfer
(RT) equation. This contribution begins presenting a method for the
formal solution of the RT equation in three-dimensional (3D) media
with horizontal periodic boundary conditions. This formal solver is
suitable for both, unpolarized and polarized 3D radiative transfer
and it can be easily combined with the iterative schemes for solving
non-LTE multilevel transfer problems that we have developed over
the last few years. We demonstrate this by showing some schematic
3D multilevel calculations that illustrate the physical effects of
horizontal radiative transfer. These Non-LTE calculations have been
carried out with our code MUGA 3D, a 3D multilevel Non-LTE code based
on the Gauss-Seidel iterative scheme that Trujillo Bueno and Fabiani
Bendicho (1995) developed for RT applications.
---------------------------------------------------------
Title: Towards the Modelling of the Second Solar Spectrum
Authors: Trujillo Bueno, J.
2007arXiv0710.5421T Altcode:
This paper addresses the modelling issue of the linearly-polarized
solar limb spectrum, which is due to scattering processes and it
offers a rich diagnostic potential for exploring solar magnetic fields
via the Hanle effect. However, this so-called second solar spectrum
is full of mysterious spectral features, which cannot be understood
with simplified polarization transfer theories, thus suggesting that
the underlying scattering physics is more complex than previously
thought. In this paper we argue that the physical understanding of
the second solar spectrum requires the consideration of scattering
processes in multilevel atomic models, taking fully into account the
transfer of atomic polarization among all the levels involved. The
consideration of lower-level atomic polarization leads to non-linear
and non-local coupled sets of equations, even for the two-level
model atom case considered in this paper. The unknowns of the problem
are the irreducible tensor components of the atomic density matrix
whose self-consistent values have first to be obtained to be able
to calculate the emergent Stokes profiles. To solve numerically this
non-LTE problem of the second kind we present some iterative methods
that are very suitable for developing a general multilevel scattering
polarization code. We demonstrate that there exists metastable-level
atomic polarization in the solar chromosphere, which suggests that
the solution to some recently-formulated "paradoxes" is to be found by
carefully revising our current ideas about the chromospheric magnetic
field.
---------------------------------------------------------
Title: Are collisions with neutral hydrogen important for modeling
the second solar spectrum of Ti I and Ca II?
Authors: Derouich, M.; Trujillo Bueno, J.; Manso Sainz, R.
2007A&A...472..269D Altcode: 2007arXiv0705.1968D
Context: The physical interpretation of scattering line polarization
offers a novel diagnostic window for exploring the thermal and magnetic
structure of the quiet regions of the solar atmosphere. <BR />Aims: We
evaluate the impact of isotropic collisions with neutral hydrogen atoms
on the scattering polarization signals of the 13 lines of multiplet 42
of Ti i and on those of the K line and of the IR triplet of Ca ii, with
emphasis on the collisional transfer rates between nearby J-levels. <BR
/>Methods: We calculate the linear polarization produced by scattering
processes in a plane-parallel layer illuminated by the radiation
field from the underlying solar photosphere. We consider realistic
multilevel models and solve the statistical equilibrium equations for
the multipolar components of the atomic density matrix. <BR />Results:
We give suitable formulae for calculating the collisional rates as a
function of temperature and hydrogen number density. We confirm that
the lower levels of the 13 lines of multiplet 42 of Ti i are completely
depolarized by elastic collisions. Upper-level depolarization caused
by the collisional transfer rates between nearby J-levels turns out
to have an unnoticeable impact on the emergent linear polarization
amplitudes, except for the λ4536 and λ4544.7 lines. Concerning
the Ca ii lines, we show that the collisional rates play no role in
the polarization of the upper level of the K line, while they have
a rather small depolarizing effect on the atomic polarization of the
metastable lower levels of the Ca ii IR triplet. <BR />Conclusions:
Although the collisional transfer rates seem to play a minor role for
most of the lines we considered in this paper, except, for example,
for the magnetically insensitive λ4536 line of Ti i, they might be
important for other atomic or molecular systems with closer J-levels
(e.g., hyperfine structured multiplets and/or molecules). Therefore,
future research in this direction will be worthwhile. <P />Appendices
A and B are only available in electronic form at http://www.aanda.org
---------------------------------------------------------
Title: The Magnetic Sensitivity of the Ba II D1 and D2 Lines of the
Fraunhofer Spectrum
Authors: Belluzzi, Luca; Trujillo Bueno, Javier; Landi Degl'Innocenti,
Egidio
2007ApJ...666..588B Altcode: 2007arXiv0704.3979B
The physical interpretation of the spectral line polarization produced
by the joint action of the Hanle and Zeeman effects offers a unique
opportunity to obtain empirical information about hidden aspects
of solar and stellar magnetism. To this end, it is important to
achieve a complete understanding of the sensitivity of the emergent
spectral line polarization to the presence of a magnetic field. Here we
present a detailed theoretical investigation on the role of resonance
scattering and magnetic fields on the polarization signals of the Ba
II D1 and D2 lines of the Fraunhofer spectrum at 4934 and 4554 Å,
respectively. We adopt a three-level model of Ba II, and we take into
account the hyperfine structure that is shown by the <SUP>135</SUP>Ba
and <SUP>137</SUP>Ba isotopes. Despite their relatively small abundance
(18%), the contribution coming from these two isotopes is indeed
fundamental for the interpretation of the polarization signals observed
in these lines. We consider an optically thin slab model, through which
we can investigate in a rigorous way the essential physical mechanisms
involved (resonance polarization, Zeeman, Paschen-Back, and Hanle
effects), avoiding complications due to radiative transfer effects. We
assume the slab to be illuminated from below by the photospheric solar
continuum radiation field, and we investigate the radiation scattered
at 90°, both in the absence and in the presence of magnetic fields,
deterministic and microturbulent. We show in particular the existence
of a differential magnetic sensitivity of the three-peak Q/I profile
that is observed in the D2 line in quiet regions close to the solar
limb, which is of great interest for magnetic field diagnostics.
---------------------------------------------------------
Title: Spicule emission profiles observed in He i 10 830 Å
Authors: Sánchez-Andrade Nuño, B.; Centeno, R.; Puschmann, K. G.;
Trujillo Bueno, J.; Blanco Rodríguez, J.; Kneer, F.
2007A&A...472L..51S Altcode: 2007arXiv0707.4421S
Aims:Off-the-limb observations with high spatial and spectral resolution
will help us understand the physical properties of spicules in the
solar chromosphere. <BR />Methods: Spectropolarimetric observations
of spicules in the He i 10 830 Å multiplet were obtained with the
Tenerife Infrared Polarimeter on the German Vacuum Tower Telescope
at the Observatorio del Teide (Tenerife, Spain). The analysis shows
the variation of the off-limb emission profiles as a function of the
distance to the visible solar limb. The ratio between the intensities
of the blue and the red components of this triplet (R=I_blue/I_red)
is an observational signature of the optical thickness along the light
path, which is related to the intensity of the coronal irradiation. <BR
/>Results: We present observations of the intensity profiles of spicules
above a quiet Sun region. The observable R as a function of the distance
to the visible limb is also given. We have compared our observational
results to the intensity ratio obtained from detailed radiative transfer
calculations in semi-empirical models of the solar atmosphere assuming
spherical geometry. The agreement is purely qualitative. We argue that
future models of the solar chromosphere and transition region should
account for the observational constraints presented here.
---------------------------------------------------------
Title: The Scattering Polarization of the Sr I λ4607 Line at the
Diffraction Limit Resolution of a 1 m Telescope
Authors: Trujillo Bueno, Javier; Shchukina, Nataliya
2007ApJ...664L.135T Altcode: 2007arXiv0706.2386T
One of the greatest challenges in solar and stellar physics in the
coming years will be to observe the second solar spectrum with a
spatial resolution significantly better than 1". This type of scattering
polarization observation would probably allow us to discover hitherto
unknown aspects of the Sun's hidden magnetism. Here we report on
some theoretical predictions for the photospheric line of Sr I at
4607 Å, which we have obtained by solving the three-dimensional
(3D) radiative transfer problem of scattering line polarization in
a realistic hydrodynamical model of the solar photosphere. We have
taken into account not only the anisotropy of the radiation field in
the 3D medium and the Hanle effect of a tangled magnetic field, but
also the symmetry-breaking effects caused by the horizontal atmospheric
inhomogeneities produced by the solar surface convection. Interestingly,
the Q/I and U/I linear polarization signals of the emergent spectral
line radiation have sizable values and fluctuations, even at the very
center of the solar disk where we observe the forward-scattering
case. The ensuing small-scale patterns in Q/I and U/I turn out to
be sensitive to the assumed magnetic field model and are of great
diagnostic value. We argue that it should be possible to observe them
with the help of a 1 m telescope equipped with adaptive optics and a
suitable polarimeter.
---------------------------------------------------------
Title: A User-Friendly Code to Diagnose Chromospheric Plasmas
Authors: Asensio Ramos, A.; Trujillo Bueno, J.
2007ASPC..368..163A Altcode: 2007arXiv0704.1723A
The physical interpretation of spectropolarimetric observations of
lines of neutral helium, such as those of the 10830 Å multiplet,
represents an excellent opportunity for investigating the magnetism
of plasma structures in the solar chromosphere. Here we present a
powerful forward modeling and inversion code that permits either to
calculate the emergent intensity and polarization for any given magnetic
field vector or to infer the dynamical and magnetic properties from
the observed Stokes profiles. This diagnostic tool is based on the
quantum theory of spectral line polarization, which self-consistently
accounts for the Hanle and Zeeman effects in the most general case of
the incomplete Paschen-Back effect regime. We also take into account
radiative transfer effects. An efficient numerical scheme based on
global optimization methods has been applied. Our Stokes inversion
code permits a fast and reliable determination of the global minimum.
---------------------------------------------------------
Title: Scattering Polarization of the Ca II Infrared Triplet as
Diagnostic of the Quiet Solar Chromosphere
Authors: Manso Sainz, R.; Trujillo Bueno, J.
2007ASPC..368..155M Altcode:
In observations close to the edge of the solar disk, the Ca II
infrared triplet has a scattering polarization pattern at the level of
10<SUP>-3</SUP> in its two strongest lines and at the 10<SUP>-4</SUP>
level in the weakest. This polarimetric sensitivity is now accessible
with modern spectropolarimeters and scattering polarization has been
observed by several authors in the Ca II infrared triplet. We discuss
here the interest of observing these lines for the detection and
mapping of magnetic fields in the quiet solar chromosphere. To this
end, we investigate theoretically the sensitivity of the polarization
pattern to the presence of magnetic fields through the Hanle effect. We
find that the Ca II 8542 Å and 8662 Å lines are mostly sensitive to
fields between 0.001 and 0.1 G, the former is also weakly sensitive
to fields between 1 and 10 G. Otherwise the polarization signals
are dependent only on the magnetic field geometry, but not on its
intensity. The 8498 Å line is highly sensitive in the whole regime
0.001-10 G, but its polarization signal is much lower. Diagnostic
diagrams giving the Q/I vs. U/I values at the line core for several
magnetic field configurations and intensities are presented. We also
discuss the sensitivity of the scattering polarization signals to the
temperature gradient of the atmospheric model.
---------------------------------------------------------
Title: Polarimetric Properties of the D<SUB>2</SUB> Lines of Alkali
Atoms
Authors: Belluzzi, L.; Landi Degl'Innocenti, E.; Trujillo Bueno, J.
2007ASPC..368..311B Altcode:
We present a theoretical investigation on the influence of a
deterministic magnetic field on the linear and circular polarization
of the Na I, K I, and Ba II D<SUB>2</SUB> lines. We describe the
three ions by means of a three-level atomic model, and we take into
account the hyperfine structure which is shown by some isotopes. We
focus on the “solar prominence case”, in which an optically thin
slab of chromospheric plasma, situated 7000 km above the visible solar
“surface”, and permeated by a magnetic field of given strength and
orientation, is illuminated from below by the continuum photospheric
radiation field.
---------------------------------------------------------
Title: A Magnetic Map of a Solar Filament
Authors: Merenda, L.; Trujillo Bueno, J.; Collados, M.
2007ASPC..368..347M Altcode:
One of the most useful diagnostic tools for the detection of inclined
magnetic fields in solar chromospheric and coronal structures is
that based on the fact that the Hanle effect in forward scattering
at the solar disk center creates linear polarization in some spectral
lines, such as those of the He I 10830 Å multiplet. Here we show the
preliminary results of an ongoing investigation on the magnetic field
of a solar filament, based on the inversion of spectropolarimetric
observations obtained with the Tenerife Infrared Polarimeter.
---------------------------------------------------------
Title: Radiative transfer modeling of the Hanle effect in convective
atmospheres
Authors: Trujillo Bueno, Javier
2007IAUS..239...44T Altcode: 2007IAUS..239...44B
No abstract at ADS
---------------------------------------------------------
Title: The Magnetic Field of Solar Chromospheric Spicules
Authors: Trujillo Bueno, J.; Ramelli, R.; Merenda, L.; Bianda, M.
2007ASPC..368..161T Altcode:
A suitable diagnostic tool for investigating the magnetism of the
solar chromosphere is the observation and theoretical modeling of
the Hanle and Zeeman effects in solar spicules. In our presentation
we highlighted the great scientific interest of this new diagnostic
window by showing how the magnetic field vector can be inferred from
spectropolarimetric observations of solar chromospheric spicules
in several spectral lines, such as those of the 10830 Å and 5876
Å multiplets of neutral helium. Our off-limb spectropolarimetric
observations of the He I 10830 Å multiplet were obtained with the
Tenerife Infrared Polarimeter (TIP) attached to the Vacuum Tower
Telescope at the Observatorio del Teide (Tenerife), while those of the
5876 Å multiplet resulted from observations with the Zurich Imaging
Polarimeter (ZIMPOL) at the Gregory Coudé Telescope of the Istituto
Ricerche Solari Locarno. The application of a Stokes profiles inversion
technique led to the following conclusion. In quiet Sun spicules the
magnetic field vector at a height of about 2000 km above the solar
visible “surface" has a typical strength of the order to 10 G and is
inclined by approximately 35° with respect to the solar local vertical
direction. In spicules observed close to active regions the strength
of the magnetic field was of the order of 50 G. The two figures below
show the off-limb Stokes profiles of the He I 5876 Å multiplet observed
in a quiet region (upper figure) and close to an active region (lower
figure). Note that in both cases Stokes U is non-zero, which is the
observational signature of the Hanle effect of an inclined magnetic
field. The change of sign in Stokes U along the spatial direction
of the spectrograph's slit can be explained by variations in the
azimuth of the magnetic field vector. Interestingly, while the Stokes
V profiles corresponding to the observed quiet region are caused by
the alignment-to-orientation transfer mechanism (see, e.g., page 607
of Landi Degl'Innocenti & Landolfi 2004), that observed in the
spicules close to the active region is dominated by the longitudinal
Zeeman effect. The interested reader will find more information in
the papers by Trujillo Bueno et al. (2005) and by Ramelli et al. (2006).
---------------------------------------------------------
Title: A Near-Infrared Line of Mn I as a Diagnostic Tool of the
Average Magnetic Energy in the Solar Photosphere
Authors: Asensio Ramos, A.; Martínez González, M. J.; López Ariste,
A.; Trujillo Bueno, J.; Collados, M.
2007ApJ...659..829A Altcode: 2006astro.ph.12389A
We report on spectropolarimetric observations of a near-IR line of Mn I
located at 15262.702 Å whose intensity and polarization profiles are
very sensitive to the presence of hyperfine structure. A theoretical
investigation of the magnetic sensitivity of this line uncovers several
interesting properties. The most important one is that the presence
of strong Paschen-Back perturbations due to the hyperfine structure
produces an intensity line profile whose shape changes according to the
absolute value of the magnetic field strength. A line ratio technique is
developed from the intrinsic variations of the line profile. This line
ratio technique is applied to spectropolarimetric observations of the
quiet solar photosphere in order to explore the probability distribution
function of the magnetic field strength. Particular attention is given
to the quietest area of the observed field of view, which was encircled
by an enhanced network region. A detailed theoretical investigation
shows that the inferred distribution yields information on the average
magnetic field strength and on the spatial scale at which the magnetic
field is organized. A first estimation gives ~250 G for the mean field
strength and a tentative value of ~0.4" for the spatial scale at which
the observed magnetic field is horizontally organized.
---------------------------------------------------------
Title: Influence of Atomic Polarization and Horizontal Illumination
on the Stokes Profiles of the He I 10830 Å Multiplet
Authors: Trujillo Bueno, Javier; Asensio Ramos, Andrés
2007ApJ...655..642T Altcode: 2006astro.ph.10128T
The polarization observed in the spectral lines of the He I 10830
Å multiplet carries valuable information on the dynamical and
magnetic properties of plasma structures in the solar chromosphere and
corona. Therefore, it is crucial to have a good physical understanding
of its sensitivity to the various competing physical mechanisms. Here
we focus on investigating the influence of atomic-level polarization
on the emergent Stokes profiles for a broad range of magnetic field
strengths, in both 90° and forward-scattering geometry. We show that,
contrary to a widespread belief, the selective emission and absorption
processes caused by the presence of atomic-level polarization may have
an important influence on the emergent linear polarization, even for
magnetic field strengths as large as 1000 G. Consequently, the modeling
of the Stokes Q- and U-profiles should not be done by taking into
account only the contribution of the transverse Zeeman effect within
the framework of the Paschen-Back effect theory, unless the magnetic
field intensity of the observed plasma structure is sensibly larger
than 1000 G. We also point out that in low-lying optically thick plasma
structures, such as those of active region filaments, the (horizontal)
radiation field generated by the structure itself may substantially
reduce the positive contribution to the anisotropy factor caused by the
(vertical) radiation field coming from the underlying solar photosphere,
so that the amount of atomic-level polarization may turn out to be
negligible. Only under such circumstances can the emergent linear
polarization of the He I 10830 Å multiplet in such structures of the
solar atmospheric plasma be dominated by the contribution caused by
the transverse Zeeman effect.
---------------------------------------------------------
Title: Off-limb spectroscopy of the He I 10830 Å multiplet:
observations vs. modelling
Authors: Sánchez-Andrade Nuño, B.; Centeno, R.; Puschmann, K. G.;
Trujillo Bueno, J.; Kneer, F.
2007msfa.conf..177S Altcode:
Spectropolarimetric observations of spicules were carried out with
the new optical setup of the Tenerife Infrared Polarimeter (TIP 2)
at the VTT, showing the variation of the He I 10830Å multiplet
off-limb emission profiles with increasing distance to the solar
visible limb. The ratio between the intensities of the blue and the
red components of this triplet (R = Iblue/Ired) is an observational
signature of the optical thickness along the light path, which, at the
same time, is proportional to the population of the lower (metastable)
level that takes part in these transitions. Our observational results
show a variation of R as a function of the distance to the limb. In
agreement with recent theoretical results we conclude that R could be
used as a diagnostic tool for downward UV coronal irradiance, which is
believed to be responsible for the population of the metastable level of
the He I 10830 Å triplet. We have compared our observational results
with the ratio obtained from detailed radiative transfer calculations
in semi-empirical models of the solar atmosphere (assuming spherical
geometry) finding a fairly poor agreement. We argue that future models
of the solar chromosphere and transition region should account for
the observational constraints presented here.
---------------------------------------------------------
Title: THEMIS observations of the Hanle effect in C_2 lines.
Authors: Asensio Ramos, A.; Trujillo Bueno, J.
2007MmSAI..78...42A Altcode:
Analysis of the Hanle effect in solar molecular lines allows us to
obtain empirical information on unresolved, tangled magnetic fields at
subresolution scales in the (granular) upflowing regions of the `quiet'
solar photosphere. Here we show observations of scattering polarization
in selected C_2 lines at increasingly closer distances to the solar
limb, pointing out that the ratio of polarization amplitudes between
suitably chosen line pairs varies in a systematic way. We interpret this
variation in terms of a microturbulent magnetic field of the order of a
few gauss whose strength decreases with height in the solar atmosphere.
---------------------------------------------------------
Title: Magnetic mappers of the quiet solar atmosphere
Authors: Trujillo Bueno, J.
2007msfa.conf..311T Altcode:
The magnetic sensitivity of the solar spectrum is caused by the
Zeeman effect and by a variety of less familiar physical mechanisms by
means of which a magnetic field can create and destroy spectral line
polarization. This paper highlights how plasma diagnostic tools based on
them could help us to explore the magnetism of the quiet regions of the
solar photosphere and chromosphere. A few suggestions for increasing the
discovery potential of some telescopes and polarimeters are also given.
---------------------------------------------------------
Title: A New Way for Exploring Solar and Stellar Magnetic Fields
Authors: Trujillo Bueno, J.
2007hsa..conf..311T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Wave propagation and shock formation in diverse magnetic
structures
Authors: Centeno, R.; Collados, M.; Trujillo Bueno, J.
2007msfa.conf..245C Altcode:
Velocity oscillations measured simultaneously at the photosphere
and the chromosphere of different solar magnetic features (sunspots,
pores and facular regions) allow us to study the properties of wave
propagation as a function of the magnetic flux of the structure. While
photospheric oscillations are similar everywhere, oscillations measured
at chromospheric heights show different amplitudes, frequencies
and stages of shock development depending on the observed magnetic
feature. The analysis via power and phase spectra, together with simple
theoretical modeling, lead to a series of results concerning wave
propagation within the range of heights of this study. We find that,
while the atmospheric cut-off frequency and the propagation properties
of the different oscillating modes depend on the magnetic feature,
in all the cases the power that reaches the high chromosphere comes
directly from the photosphere by means of linear wave propagation
rather than from non-linear interaction of modes.
---------------------------------------------------------
Title: Oscillations and Wave Propagation in Different Solar Magnetic
Features
Authors: Centeno, R.; Collados, M.; Trujillo Bueno, J.
2006ASPC..358..465C Altcode:
We present the results of the analysis of temporal series of
spectro-polarimetric data measured simultaneously in the photospheric
Si I 10827 Å line and the chromospheric He I 10830 Å triplet, on
top of two different targets: a facular region and the umbra of a
sunspot. The full Stokes inversion of both spectral features gives us
the temporal variability of the physical conditions at two different
regions in the solar atmosphere, allowing us to compare the LOS velocity
oscillations at the photosphere and the chromosphere, and infer the
main characteristics of wave propagation in both magnetic structures.
---------------------------------------------------------
Title: The Hanle and Zeeman Effects in the Ba II D<SUB>2</SUB> Line
Authors: Belluzzi, L.; Trujillo Bueno, J.; Landi Degl'Innocenti, E.
2006ASPC..358..459B Altcode:
We present a theoretical investigation on the influence of the magnetic
field on the linear and circular polarization of the Ba II D<SUB>2</SUB>
line at 4554 Å, through the Hanle and Zeeman effects. We show in
particular the existence of a differential magnetic sensitivity of
the three-peak structure of the Q/I profile observed for this line,
which is of interest for magnetic field diagnostics.
---------------------------------------------------------
Title: The Hanle Effect in Atomic and Molecular Lines: A New Look
at the Sun's Hidden Magnetism
Authors: Trujillo Bueno, J.; Asensio Ramos, A.; Shchukina, N.
2006ASPC..358..269T Altcode: 2006astro.ph.12678T
This paper reviews some of the most recent advances in the application
of the Hanle effect to solar physics, and how these developments are
allowing us to explore the magnetism of the photospheric regions that
look “empty” in solar magnetograms--that is, the Sun's “hidden”
magnetism. In particular, we show how a joint analysis of the Hanle
effect in atomic and molecular lines indicates that there is a vast
amount of hidden magnetic energy and unsigned magnetic flux localized in
the (intergranular) downflowing regions of the quiet solar photosphere,
carried mainly by tangled fields at sub-resolution scales with strengths
between the equipartition field values and ∼1 kG. <P />This article
combines in one contribution Trujillo Bueno's invited keynote paper
and the contributed papers by Asensio Ramos & Trujillo Bueno and
by Shchukina & Trujillo Bueno.
---------------------------------------------------------
Title: Three-Dimensional Radiative Transfer Modeling of the Scattering
Polarization in MgH Lines
Authors: Asensio Ramos, A.; Trujillo Bueno, J.
2006ASPC..358..318A Altcode:
Analysis of the Hanle effect in solar molecular lines allows us to
obtain empirical information on hidden, mixed-polarity magnetic fields
at subresolution scales in the (granular) upflowing regions of the
`quiet' solar photosphere. Here we report that collisions seem to be
very efficient in depolarizing the rotational levels of MgH lines. This
has the interesting consequence that in the upflowing regions of the
quiet solar photosphere the strength of the hidden magnetic field cannot
be sensibly larger than 10 G, assuming the simplest case of a single
valued microturbulent field that fills the entire upflowing photospheric
volume. Alternatively, an equally good theoretical fit to the observed
scattering polarization amplitudes can be achieved by assuming that the
rate of depolarizing collisions is an order of magnitude smaller than
in the previous collisionally dominated case, but then the required
strength of the hidden field in the upflowing regions turns out to
be unrealistically high. These constraints reinforce our previously
obtained conclusion that there is a vast amount of hidden magnetic
energy and unsigned magnetic flux localized in the (intergranular)
downflowing regions of the quiet solar photosphere. This work has been
presented by tet{a4 AT05}.
---------------------------------------------------------
Title: Spectro-Polarimetry of Solar Prominences
Authors: Ramelli, R.; Bianda, M.; Trujillo Bueno, J.; Merenda, L.;
Stenflo, J. O.
2006ASPC..358..471R Altcode: 2009arXiv0906.2342R
A large set of high-precision, full-Stokes spectro-polarimetric
observations of prominences in He I D<SUB>3</SUB>, Hα, and Hβ lines
has been recorded with the ZIMPOL polarimeter at the Gregory-Coudé
Telescope in Locarno. The observational technique allows us to
obtain measurements free from seeing-induced spurious effects. The
instrumental polarization is well under control and taken into account
in the data analysis. We present our observational results for each
of the lines mentioned above. Of particular interest is that most
of our Hα measurements show <P />antisymmetric V profiles that are
a characteristic signature of the Zeeman effect in the prominence
plasma. A Stokes inversion technique based on the quantum theory of the
Hanle and Zeeman effects is being applied on observed Stokes profiles
in the He I D<SUB>3</SUB> line in order to obtain information on the
magnetic field vector that confines the prominence plasma.
---------------------------------------------------------
Title: Spectro-Polarimetric Observations of Filaments in Hα and He
I D<SUB>3</SUB>
Authors: Bianda, M.; Ramelli, R.; Trujillo Bueno, J.; Stenflo, J. O.
2006ASPC..358..454B Altcode:
Recordings of the full Stokes vector of filaments in the Hα and He I
D<SUB>3</SUB> lines were obtained at the Gregory-Coudé telescope in
Locarno with the polarimeter ZIMPOL. The aim was to perform preliminary
studies to explore the presence of forward scattering polarization. The
observations show linear polarization signatures, whose interpretation
is still being investigated, although it seems likely that forward
scattering is indeed involved.
---------------------------------------------------------
Title: Erratum: “Polynomial Approximants for the Calculation
of Polarization Profiles in the He I 10830 Å Multiplet” (<A
href="bib_query?2005ApJS...160..312S">ApJS, 160, 312 [2005]</A>)
Authors: Socas-Navarro, H.; Trujillo Bueno, J.; Landi Degl'Innocenti,
E.
2006ApJS..166..441S Altcode:
In our published paper there is an error in the order of the rows in
Tables 1 through 6. We stated in the paper that the components are
sorted in the order of increasing wavelengths in the linear Zeeman
splitting (LZS) regime. However, in the published tables the values for
the σ<SUP>+</SUP> and σ<SUP>-</SUP> components appear reversed. As
a result, researchers trying to implement our polynomial approximants
might apply the incomplete Paschen-Back splitting (IPBS) corrections
to the wrong components. To avoid any possible confusion, here we
reproduce the tables with the correct sorting (i.e., in the order of
increasing wavelengths in the LZS regime). For clarity, we have also
replaced the σ<SUP>+/-</SUP> notation with σ<SUP>red/blue</SUP>. <P
/>We thank Rebecca Centeno for bringing this error to our attention.
---------------------------------------------------------
Title: Determination of the Magnetic Field Vector via the Hanle and
Zeeman Effects in the He I λ10830 Multiplet: Evidence for Nearly
Vertical Magnetic Fields in a Polar Crown Prominence
Authors: Merenda, L.; Trujillo Bueno, J.; Landi Degl'Innocenti, E.;
Collados, M.
2006ApJ...642..554M Altcode:
The magnetic field is the key physical quantity responsible for the
formation, stability, and evolution of solar prominences (ribbons of
cool dense gas embedded in the hot tenuous corona). Therefore, it is
important to obtain good empirical knowledge of the three-dimensional
structure of prominence magnetic fields. Here we show how the magnetic
field vector can be inferred via the physical interpretation of
spectropolarimetric observations in the He I λ10830 multiplet. To this
end, we have developed an inversion code based on the quantum theory
of the Hanle and Zeeman effects and on a few modeling assumptions. We
show an application to full Stokes vector observations of a polar crown
prominence that, in the slit-jaw Hα image, showed nearly vertical
plasma structures. Our results provide evidence for magnetic fields
on the order of 30 G inclined by about 25° with respect to the local
solar vertical direction. Of additional interest is that the inferred
nearly vertical magnetic field vector appears to be slightly rotating
around a fixed direction in space as one proceeds along the direction
of the spectrograph's slit. While these results provide new light on
the three-dimensional geometry of the magnetic fields that confine the
plasma of polar crown prominences, they also urge us to develop improved
solar prominence models and to pursue new diagnostic investigations.
---------------------------------------------------------
Title: Spectropolarimetric Investigation of the Propagation of
Magnetoacoustic Waves and Shock Formation in Sunspot Atmospheres
Authors: Centeno, Rebecca; Collados, Manuel; Trujillo Bueno, Javier
2006ApJ...640.1153C Altcode: 2005astro.ph.12096C
Velocity oscillations in sunspot umbrae have been measured
simultaneously in two spectral lines: the photospheric Si I λ10827
line and the chromospheric He I λ10830 multiplet. From the full Stokes
inversion of temporal series of spectropolarimetric observations, we
retrieved, among other parameters, the line-of-sight velocity temporal
variations at photospheric and chromospheric heights. Chromospheric
velocity oscillations show a 3 minute period with a clear sawtooth
shape typical of propagating shock wave fronts. Photospheric velocity
oscillations have basically a 5 minute period, although the power
spectrum also shows a secondary peak in the 3 minute band that has
been proven to be a predecessor for its chromospheric counterpart. The
derived phase spectra yield a value of the atmospheric cutoff frequency
around 4 mHz and give evidence for the upward propagation of higher
frequency oscillation modes. The phase spectrum has been reproduced with
a simple model of linear vertical propagation of slow magnetoacoustic
waves in a stratified magnetized atmosphere that accounts for radiative
losses through Newton's cooling law. The model explains the main
features in the phase spectrum and allows us to compute the theoretical
time delay between the photospheric and chromospheric signals, which
happens to have a strong dependence on frequency. We find a very good
agreement between this and the time delay obtained directly from the
cross-correlation of photospheric and chromospheric velocity maps
filtered around the 6 mHz band. This allows us to infer that the 3
minute power observed at chromospheric heights comes directly from
the photosphere by means of linear wave propagation, rather than from
nonlinear interaction of 5 minute (and/or higher frequency) modes.
---------------------------------------------------------
Title: A qualitative interpretation of the second solar spectrum of
Ce ll
Authors: Manso Sainz, R.; Landi Degl'Innocenti, E.; Trujillo Bueno, J.
2006A&A...447.1125M Altcode: 2005astro.ph.11011M
This is a theoretical investigation on the formation of the linearly
polarized line spectrum of ionized cerium in the sun. We calculate the
scattering line polarization pattern emergent from a plane-parallel
layer of Ce ii atoms illuminated from below by the photospheric
radiation field, taking into account the differential pumping induced
in the various magnetic sublevels by the anisotropic radiation
field. We find that the line polarization pattern calculated with
this simple model is in good qualitative agreement with reported
observations. Interestingly, the agreement improves when some
amount of atomic level depolarization is considered. We find that
the best fit to the observations corresponds to the situation
where the ground and metastable levels are depolarized to about
one fifth of the corresponding value obtained in the absence of
any depolarizing mechanism. One possibility to have this situation
is that the depolarizing rate value of elastic collisions is exactly
D=10^6~s<SUP>-1</SUP>, which is rather unlikely. Therefore, we interpret
that fact as due to the presence of a turbulent magnetic field in
the limit of saturated Hanle effect for the lower-levels. For this
turbulent magnetic field we obtain a lower limit of 0.8 Gauss and an
upper limit of 200-300 Gauss.
---------------------------------------------------------
Title: Theory and Modeling of the Zeeman and Paschen-Back Effects
in Molecular Lines
Authors: Asensio Ramos, A.; Trujillo Bueno, J.
2006ApJ...636..548A Altcode: 2005astro.ph.10262A
This paper describes a very general approach to the calculation of
the Zeeman splitting effect produced by an external magnetic field
on the rotational levels of diatomic molecules. The method is valid
for arbitrary values of the total electronic spin and of the magnetic
field strength-that is, it holds for molecular electronic states of
any multiplicity and for both the Zeeman and incomplete Paschen-Back
regimes. It is based on an efficient numerical diagonalization of
the effective Zeeman Hamiltonian, which can incorporate easily all the
contributions one may eventually be interested in, such as the hyperfine
interaction of the external magnetic field with the spin motions of
the nuclei. The reliability of the method is demonstrated by comparing
our results with previous ones obtained via formulae valid only for
doublet states. We also present results for molecular transitions
arising between nondoublet electronic states, illustrating that their
Zeeman patterns show signatures produced by the Paschen-Back effect.
---------------------------------------------------------
Title: Very Efficient Methods for Multilevel Radiative Transfer in
Atomic and Molecular Lines
Authors: Asensio Ramos, A.; Trujillo Bueno, J.
2006EAS....18...25A Altcode: 2005astro.ph.12248A
The development of fast numerical methods for multilevel radiative
transfer (RT) applications often leads to important breakthroughs
in astrophysics, because they allow the investigation of problems
that could not be properly tackled using the methods previously
available. Probably, the most familiar example is the so-called
Multilevel Accelerated Λ-Iteration (MALI) technique of Rybicki &
Hummer for the case of a local approximate operator, which is based
on Jacobi iteration. However, there are superior operator-splitting
methods, based on Gauss-Seidel (GS) and Successive Overrelaxation (SOR)
iteration, which provide a dramatic increase in the speed with which
non-LTE multilevel transfer problems can be solved in one, two and
three-dimensional geometries. Such RT methods, which were introduced
by Trujillo Bueno & Fabiani Bendicho ten years ago, are the main
subject of the first part of this paper. We show in some detail how they
can be applied for solving multilevel RT problems in spherical geometry,
for both atomic and molecular line transitions. The second part of the
article addresses the issue of the calculation of the molecular number
densities when the approximation of instantaneous chemical equilibrium
turns out to be inadequate, which happens to be the case whenever the
dynamical time scales of the astrophysical plasma under consideration
are much shorter than the time needed by the molecules to form.
---------------------------------------------------------
Title: A Gentle Introduction to the Physics of Spectral Line
Polarization
Authors: Trujillo Bueno, Javier
2006spse.conf...77T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Quantum Spectropolarimetry and the Sun's Hidden Magnetism
Authors: Trujillo Bueno, J.
2005ESASP.600E...7T Altcode: 2005ESPM...11....7T; 2005dysu.confE...7T
No abstract at ADS
---------------------------------------------------------
Title: Evidence for Fine Structure in the Chromospheric Umbral
Oscillation
Authors: Centeno, R.; Socas-Navarro, H.; Collados, M.; Trujillo
Bueno, J.
2005ApJ...635..670C Altcode: 2005astro.ph.10740C
Novel spectropolarimetric observations of the He I multiplet are
used to explore the dynamics of the chromospheric oscillation above
sunspot umbrae. The results presented here provide strong evidence
in support of the two-component model proposed by Socas-Navarro
and coauthors. According to this model, the waves propagate only
inside channels of subarcsecond width (the “active” component),
whereas the rest of the umbra remains nearly at rest (the “quiet”
component). Although the observations support the fundamental elements
of that model, there is one particular aspect that is not compatible
with our data. We find that, contrary to the scenario as originally
proposed, the active component remains through the entire oscillation
cycle and harbors both the upflowing and the downflowing phase of
the oscillation.
---------------------------------------------------------
Title: Evidence for Collisional Depolarization in the MgH Lines of
the Second Solar Spectrum
Authors: Asensio Ramos, A.; Trujillo Bueno, J.
2005ApJ...635L.109A Altcode: 2005astro.ph.10711A
The analysis of the Hanle effect in solar molecular lines allows us to
obtain empirical information on hidden, mixed-polarity magnetic fields
at subresolution scales in the (granular) upflowing regions of the
“quiet” solar photosphere. Here we report that collisions seem to be
very efficient in depolarizing the rotational levels of MgH lines. This
has the interesting consequence that in the upflowing regions of the
quiet solar photosphere the strength of the hidden magnetic field cannot
be much larger than 10 G, assuming the simplest case of a single-valued
microturbulent field that fills the entire upflowing photospheric
volume. Alternatively, an equally good theoretical fit to the observed
scattering polarization amplitudes can be achieved by assuming that the
rate of depolarizing collisions is an order of magnitude smaller than
in the previous collisionally dominated case, but then the required
strength of the hidden field in the upflowing regions turns out to
be unrealistically high. These constraints reinforce our previously
obtained conclusion that there is a vast amount of hidden magnetic
energy and unsigned magnetic flux localized in the (intergranular)
downflowing regions of the quiet solar photosphere.
---------------------------------------------------------
Title: The scientific case for spectropolarimetry from space:
a novel diagnostic window on cosmic magnetic fields
Authors: Trujillo Bueno, J.; Landi Degl'Innocenti, E.; Casini, R.;
Martínez Pillet, V.
2005ESASP.588..203T Altcode: 2005tssc.conf..203T
No abstract at ADS
---------------------------------------------------------
Title: Determination of the Magnetic Field Vector in a Polar Crown
Prominence via the Hanle and Zeeman Effects in the He I 10830 Å
Multiplet.
Authors: Merenda, L.; Trujillo Bueno, J.; Landi Degl'Innocenti, E.;
Collados, M.
2005ESASP.596E..18M Altcode: 2005ccmf.confE..18M
No abstract at ADS
---------------------------------------------------------
Title: Spectropolarimetric Observations of Prominences and Spicules,
and Magnetic Field Diagnostics
Authors: Ramelli, R.; Bianda, M.; Trujillo Bueno, J.; Merenda, L.;
Stenflo, J. O.
2005ESASP.596E..82R Altcode: 2005ccmf.confE..82R
No abstract at ADS
---------------------------------------------------------
Title: The Scientific Case for Quantum Spectropolarimetry from Space
Authors: Trujillo Bueno, J.; Landi Degl'Innocenti, E.; Casini, R.;
Martínez Pillet, V.
2005ESASP.596E...4T Altcode: 2005ccmf.confE...4T
No abstract at ADS
---------------------------------------------------------
Title: Polynomial Approximants for the Calculation of Polarization
Profiles in the He I 10830 Å Multiplet
Authors: Socas-Navarro, H.; Trujillo Bueno, J.; Landi Degl'Innocenti,
E.
2005ApJS..160..312S Altcode: 2005astro.ph..5321S
The He I multiplet at 10830 Å is formed in the incomplete
Paschen-Back regime for typical conditions found in solar and stellar
atmospheres. The positions and strengths of the various components
that form the Zeeman structure of this multiplet in the Paschen-Back
regime are approximated here by polynomials. The fitting errors
are smaller than ~10<SUP>-2</SUP> mÅ in the component positions
and ~10<SUP>-3</SUP> in the relative strengths. The approximant
polynomials allow for a very fast implementation of the incomplete
Paschen-Back regime in numerical codes for the synthesis and inversion
of polarization profiles in this important multiplet.
---------------------------------------------------------
Title: The iron and oxygen abundances in the metal-poor star HD
140283 and in the Sun
Authors: Shchukina, N. G.; Vasiljeva, I. E.; Trujillo Bueno, J.
2005KFNTS...5...95S Altcode:
We present the results of a theoretical investigation of the impact
of NLTE effects and of granulation inhomogeneities on the iron and
oxygen abundances in the metal-poor star HD 140283 and in the Sun. Our
analysis is based on both the classical one-dimensional (1D) stellar
atmosphere models and on a new generation of three-dimensional (3D)
hydrodynamical models. We consider the Sun as a reference star. The
solar iron and oxygen abundances are redefined.
---------------------------------------------------------
Title: Dichroic Masers Due to Radiation Anisotropy and the Influence
of the Hanle Effect on the Circumstellar SiO Polarization
Authors: Asensio Ramos, A.; Landi Degl'Innocenti, E.; Trujillo
Bueno, J.
2005ApJ...625..985A Altcode: 2005astro.ph..2405A
The theory of the generation and transfer of polarized radiation, mainly
developed for interpreting solar spectropolarimetric observations,
allows us to reconsider, in a more rigorous and elegant way, a physical
mechanism that has been suggested some years ago to interpret the high
degree of polarization often observed in astronomical masers. This
mechanism, for which the name of “dichroic maser” is proposed,
can operate when a low-density molecular cloud is illuminated by
an anisotropic source of radiation (e.g., a nearby star). Here we
investigate completely unsaturated masers and show that selective
stimulated emission processes are capable of producing highly polarized
maser radiation in a nonmagnetic environment. The polarization of
the maser radiation is linear and is directed tangentially to a ring
equidistant to the central star. We show that the Hanle effect due
to the presence of a magnetic field can produce a rotation (from the
tangential direction) of the polarization by more that 45° for some
selected combinations of the strength, inclination, and azimuth of the
magnetic field vector. However, these very same conditions produce a
drastic inhibition of the maser effect. The rotations of about 90°
observed in SiO masers in the evolved stars TX Cam by Kemball &
Diamond and IRC +10011 by Desmurs and coworkers may then be explained
by a local modification of the anisotropy of the radiation field,
being transformed from mainly radial to mainly tangential.
---------------------------------------------------------
Title: Observation and Modeling of Anomalous CN Polarization Profiles
Produced by the Molecular Paschen-Back Effect in Sunspots
Authors: Asensio Ramos, A.; Trujillo Bueno, J.; Collados, M.
2005ApJ...623L..57A Altcode: 2005astro.ph..5076A
We report novel spectropolarimetric observations of sunspots carried
out with the Tenerife Infrared Polarimeter in a near-IR spectral
region around 15410 Å, which is known to contain two groups of
prominent OH lines that show circular polarization signals of
opposite polarity. Surrounding these well-known OH lines, we have
discovered the presence of CN lines of the Δv=1 band that show
anomalous polarization profiles. Although the Stokes V signals of
the OH lines are antisymmetric and of a sizable amplitude, the CN
lines show almost negligible circular polarization. On the contrary,
the linear polarization signals turn out to be much stronger in the
CN lines than in the OH lines. Interestingly, these CN lines present
striking antisymmetric linear polarization profiles, which we are able
to explain and model via the Paschen-Back effect theory for diatomic
molecules. The presence of such peculiar CN lines in the same spectral
region of the OH lines may be useful to improve our empirical knowledge
of solar magnetic fields via the simultaneous observation and modeling
of the transverse and longitudinal Zeeman effects in two different
molecular species.
---------------------------------------------------------
Title: Full Stokes Spectropolarimetry of Hα in Prominences
Authors: López Ariste, A.; Casini, R.; Paletou, F.; Tomczyk, S.;
Lites, B. W.; Semel, M.; Landi Degl'Innocenti, E.; Trujillo Bueno,
J.; Balasubramaniam, K. S.
2005ApJ...621L.145L Altcode:
We report on spectropolarimetric observations of Hα in prominences
made with the Télescope Héliographique pour l'Etude du Magnétisme et
des Instabilités Solaires and the High Altitude Observatory/Advanced
Stokes Polarimeter. Stokes Q and U show the expected profile shape from
resonance scattering polarization and the Hanle effect. In contrast,
most of the time, Stokes V does not show the antisymmetric profile shape
typical of the Zeeman effect but a profile that indicates the presence
of strong atomic orientation in the hydrogen levels, to an extent that
cannot be explained by invoking the alignment-to-orientation transfer
mechanism induced by the prominence magnetic field. We found that the
largest signal amplitudes of Stokes V (comparable to that of Stokes
Q and U) could be produced by a process of selective absorption of
circularly polarized radiation from the photosphere, which requires
that the prominence be in the vicinity of an active region. Although
recent observations of active region filaments indicate such a
selective absorption mechanism as a plausible explanation of the
anomalous signals observed, the particular set of conditions that
must be met suggest that a different explanation may be required
to explain the almost ubiquitous symmetric V signal observed in Hα
prominences. Therefore, we speculate that an alternative mechanism
inducing strong atomic orientation at the observed level could be due
to the presence of electric fields inducing an electric Hanle effect
on Hα. Although we are still working toward a careful modeling of
this effect, including both electric and magnetic fields, we present
some preliminary considerations that seem to support this possibility.
---------------------------------------------------------
Title: The Hanle and Zeeman Effects in Solar Spicules: A Novel
Diagnostic Window on Chromospheric Magnetism
Authors: Trujillo Bueno, J.; Merenda, L.; Centeno, R.; Collados, M.;
Landi Degl'Innocenti, E.
2005ApJ...619L.191T Altcode: 2005astro.ph..1533T; 2005astro.ph..1533B
An attractive diagnostic tool for investigating the magnetism of the
solar chromosphere is the observation and theoretical modeling of
the Hanle and Zeeman effects in spicules, as shown in this Letter for
the first time. Here we report on spectropolarimetric observations of
solar chromospheric spicules in the He I λ10830 multiplet and on their
theoretical modeling accounting for radiative transfer effects. We find
that the magnetic field in the observed (quiet-Sun) spicular material at
a height of about 2000 km above the visible solar surface has a strength
of the order of 10 G and is inclined by approximately 35<SUP>deg</SUP>
with respect to the local vertical direction. Our empirical finding
based on full Stokes vector spectropolarimetry should be taken into
account in future magnetohydrodynamical simulations of spicules.
---------------------------------------------------------
Title: The Impact of Non-LTE Effects and Granulation Inhomogeneities
on the Derived Iron and Oxygen Abundances in Metal-Poor Halo Stars
Authors: Shchukina, N. G.; Trujillo Bueno, J.; Asplund, M.
2005ApJ...618..939S Altcode: 2004astro.ph.10475S
This paper presents the results of a detailed theoretical investigation
of the impact of non-LTE (NLTE) effects and of granulation
inhomogeneities on the derived iron and oxygen abundances in the
metal-poor halo subgiant HD 140283. Our analysis is based on both the
“classical” one-dimensional stellar atmosphere models and on the
new generation of three-dimensional hydrodynamic models. The NLTE
calculations presented here have been carried out without inelastic
collisions with neutral hydrogen atoms. We find that if NLTE effects
are taken into account when synthesizing the Fe I spectrum in both
types of atmospheric models, then the derived iron abundance turns out
to be very similar in both cases. The emergent spectral line profiles
in both models are very much weaker in NLTE than in LTE because the
UV overionization mechanism produces a very strong underpopulation
of the Fe I levels, in particular in the granular regions of the
three-dimensional model. As a result, the NLTE effects on the derived
iron abundance are very important, amounting to ~0.9 and to ~0.6 dex in
the three- and one-dimensional cases, respectively. On the other hand,
we find that NLTE and three-dimensional effects have to be taken into
account for a reliable determination of the iron abundance from weak Fe
II lines, because the significant overexcitation of their upper levels
in the granular regions tend to produce emission features. As a result,
such Fe II lines are weaker than in LTE and the abundance correction
amounts to ~0.4 dex for the three-dimensional case. We also derive
the oxygen-to-iron abundance ratio in the metal-poor star HD 140283
by using the O I triplet at 7772-7775 Å and the forbidden [O I] line
at 6300 Å. Our results for the oxygen abundance confirm the values
reported in some recent investigations. While the oxygen abundance
derived from the O I IR triplet is not very sensitive to the presence
of granulation inhomogeneities, such three-dimensional effects amount to
~-0.2 dex for the [O I] line. The NLTE abundance correction for the O I
IR triplet turns out to be -0.2 dex, approximately. Interestingly, when
both NLTE and three-dimensional effects are taken into account there
still remain significant discrepancies in the iron abundances derived
from Fe I and Fe II lines, as well as in the oxygen abundances inferred
from the O I and [O I] lines. We conclude that the discrepancies could
be due to uncertainties in the stellar parameters of this metal-poor
star. We argue that adopting T<SUB>eff</SUB>~5600 K (instead of
T<SUB>eff</SUB>~5700 K) and [Fe/H]~-2.0 (instead of [Fe/H]~-2.5)
substantially reduces the discrepancies in the abundances of iron and
oxygen inferred from several spectral lines. Under such circumstances,
we find [O/Fe]~0.5 at [Fe/H]=-2. Obviously, our tentative conclusion
that the metallicity of this type of metal-poor star is significantly
larger than previously thought may have far-reaching implications in
stellar astrophysics.
---------------------------------------------------------
Title: Concerning the Existence of a “Turbulent” Magnetic Field
in the Quiet Sun
Authors: Manso Sainz, Rafael; Landi Degl'Innocenti, Egidio; Trujillo
Bueno, Javier
2004ApJ...614L..89M Altcode: 2004astro.ph..8360M
We report on the a<SUP>5</SUP>F-y<SUP>5</SUP>F<SUP>o</SUP> multiplet
of Ti I and its interest for the study of “turbulent” magnetic
fields in the quiet solar photosphere. In particular, we argue that
the sizable scattering polarization signal of the 4536 Å line (whose
lower and upper levels have Landé factors equal to zero), relative
to the rest of the lines in the multiplet, gives direct evidence for
the existence of a ubiquitous, unresolved magnetic field. We cannot
determine precisely the strength of the magnetic field, but its very
existence is evidenced by the differential Hanle effect technique that
this Ti I multiplet provides.
---------------------------------------------------------
Title: Signatures of Incomplete Paschen-Back Splitting in the
Polarization Profiles of the He I λ10830 Multiplet
Authors: Socas-Navarro, H.; Trujillo Bueno, J.; Landi Degl'Innocenti,
E.
2004ApJ...612.1175S Altcode: 2004astro.ph..9005S
We investigate the formation of polarization profiles induced by a
magnetic field in the He I multiplet at 10830 Å. Our analysis considers
the Zeeman splitting in the incomplete Paschen-Back regime. The effects
turn out to be important and produce measurable signatures on the
profiles, even for fields significantly weaker than the level-crossing
field (~400 G). When compared to profiles calculated with the usual
linear Zeeman effect, the incomplete Paschen-Back profiles exhibit
the following conspicuous differences: (1) a non-Doppler blueshift
of the Stokes V zero-crossing wavelength of the blue component;
(2) area and peak asymmetries, even in the absence of velocity and
magnetic gradients; and (3) a ~25% reduction in the amplitude of
the red component. These features do not vanish in the weak-field
limit. The spectral signatures that we analyze in this paper may be
found in previous observations published in the literature.
---------------------------------------------------------
Title: Observation of the Molecular Zeeman Effect in the G Band
Authors: Asensio Ramos, A.; Trujillo Bueno, J.; Bianda, M.; Manso
Sainz, R.; Uitenbroek, H.
2004ApJ...611L..61A Altcode: 2004astro.ph..7332A; 2004astro.ph..7332R
Here we report on the first observational investigation of the
Zeeman effect in the G band around 4305 Å. Our spectropolarimetric
observations of sunspots with the Zürich Imaging Polarimeter at the
Istituto Ricerche Solari Locarno confirm our previous theoretical
prediction that the molecular Zeeman effect produces measurable
circular polarization signatures in several CH lines that are not
overlapped with atomic transitions. We also find both circular and
linear polarization signals produced by atomic lines whose wavelengths
lie in the G-band spectral region. Together, such molecular and atomic
lines are potentially important for empirical investigations of solar
and stellar magnetism. For instance, a comparison between observed and
calculated Stokes profiles suggests that the thermodynamical and/or
magnetic properties of the photospheric regions of sunspot umbrae are
horizontally structured with a component that might be associated with
umbral dots.
---------------------------------------------------------
Title: A substantial amount of hidden magnetic energy in the quiet Sun
Authors: Trujillo Bueno, J.; Shchukina, N.; Asensio Ramos, A.
2004Natur.430..326T Altcode: 2004astro.ph..9004T; 2004astro.ph..9004B
Deciphering and understanding the small-scale magnetic activity of the
quiet solar photosphere should help to solve many of the key problems
of solar and stellar physics, such as the magnetic coupling to the
outer atmosphere and the coronal heating. At present, we can see only
~1 per cent of the complex magnetism of the quiet Sun, which highlights
the need to develop a reliable way to investigate the remaining 99 per
cent. Here we report three-dimensional radiative transfer modelling of
scattering polarization in atomic and molecular lines that indicates
the presence of hidden, mixed-polarity fields on subresolution
scales. Combining this modelling with recent observational data, we
find a ubiquitous tangled magnetic field with an average strength of
~130G, which is much stronger in the intergranular regions of solar
surface convection than in the granular regions. So the average magnetic
energy density in the quiet solar photosphere is at least two orders
of magnitude greater than that derived from simplistic one-dimensional
investigations, and sufficient to balance radiative energy losses from
the solar chromosphere.
---------------------------------------------------------
Title: Dynamics of an enhanced network region observed in Hα
Authors: Al, N.; Bendlin, C.; Hirzberger, J.; Kneer, F.; Trujillo
Bueno, J.
2004A&A...418.1131A Altcode:
This investigation is based on Hα observations of high spatial
resolution. They stem from an enhanced network region near disk centre
of the sun and consist of broad-band and narrow-band images taken with
the two-dimensional “Göttingen” Fabry-Perot spectrometer mounted in
the Vacuum Tower Telescope at the Observatorio del Teide/Tenerife. The
“lambdameter method” was applied to derive intensity and velocity
maps over the two-dimensional field of view reflecting the behaviour
of these parameters in the solar chromosphere. The determination of
the source function, the line-of-sight (LOS) velocity, the Doppler
width and the optical depth was based on Beckers' cloud model
(Beckers \cite{beckers}). From the LOS velocity distribution along
the Hα structures we conclude that ballistic motions are unlikely to
prevail. Especially the bright Hα features cannot be explained by the
cloud model. It is shown how, instead, two-dimensional non-LTE radiative
transfer calculations of embedded chromospheric structures lead to
reasonable agreement with the observed line profiles from these bright
features. It is found that many of the bright fibril-like structures
near dark fibrils can be explained by radiation which is blocked by
absorbing material at large heights and escapes through less opaque
regions. We estimate the number densities and the temperature. With
these and with the measured velocities, the kinetic energy flux and
the enthalpy flux related to the motions of the fine structures can
be calculated. Both fall short by at least an order of magnitude of
covering energy losses by radiation of active chromospheric regions.
---------------------------------------------------------
Title: The Zeeman Effect in the G Band
Authors: Uitenbroek, H.; Miller-Ricci, E.; Asensio Ramos, A.; Trujillo
Bueno, J.
2004ApJ...604..960U Altcode: 2004astro.ph..1467U
We investigate the possibility of measuring magnetic field strength in
G-band bright points through the analysis of Zeeman polarization in
molecular CH lines. To this end we solve the equations of polarized
radiative transfer in the G band through a standard plane-parallel
model of the solar atmosphere with an imposed magnetic field
and through a more realistic snapshot from a simulation of solar
magnetoconvection. This region of the spectrum is crowded with many
atomic and molecular lines. Nevertheless, we find several instances of
isolated groups of CH lines that are predicted to produce a measurable
Stokes V signal in the presence of magnetic fields. In part this is
possible because the effective Landé factors of lines in the stronger
main branch of the CH A<SUP>2</SUP>Δ-X<SUP>2</SUP>Π transition
tend to zero rather quickly for increasing total angular momentum J,
resulting in a Stokes V spectrum of the G band that is less crowded than
the corresponding Stokes I spectrum. We indicate that, by contrast,
the effective Landé factors of the R and P satellite subbranches of
this transition tend to +/-1 for increasing J. However, these lines
are in general considerably weaker and do not contribute significantly
to the polarization signal. In one wavelength location near 430.4 nm,
the overlap of several magnetically sensitive and nonsensitive CH lines
is predicted to result in a single-lobed Stokes V profile, raising
the possibility of high spatial resolution narrowband polarimetric
imaging. In the magnetoconvection snapshot we find circular polarization
signals of the order of 1%, prompting us to conclude that measuring
magnetic field strength in small-scale elements through the Zeeman
effect in CH lines is a realistic prospect.
---------------------------------------------------------
Title: Detection of Polarization from the
E<SUP>4</SUP>Π-A<SUP>4</SUP>Π System of FeH in Sunspot Spectra
Authors: Asensio Ramos, A.; Trujillo Bueno, J.; Collados, M.
2004ApJ...603L.125A Altcode: 2004astro.ph..1597A; 2004astro.ph..1597R
Here we report the first detection of polarization signals
induced by the Zeeman effect in spectral lines of the
E<SUP>4</SUP>Π-A<SUP>4</SUP>Π system of FeH located around 1.6
μm. Motivated by the tentative detection of this band in the
intensity spectrum of late-type dwarfs, we have investigated the
full Stokes sunspot spectrum and have found circular and linear
polarization signatures that we associate with the FeH lines of the
E<SUP>4</SUP>Π-A<SUP>4</SUP>Π band system. We investigate the Zeeman
effect in these molecular transitions and point out that in Hund's case
(a) coupling, the effective Landé factors are never negative. For this
reason, the fact that our spectropolarimetric observations indicate that
the Landé factors of pairs of FeH lines have opposite signs prompts
us to conclude that the E<SUP>4</SUP>Π-A<SUP>4</SUP>Π system must be
in intermediate angular momentum coupling between Hund's cases (a) and
(b). We emphasize that theoretical and/or laboratory investigations of
this molecular system are urgently needed for exploiting its promising
diagnostic capabilities.
---------------------------------------------------------
Title: The magnetic fields of the quiet solar photosphere
Authors: Shchukina, Nataliya G.; Trujillo Bueno, Javier
2004IAUS..223..483S Altcode: 2005IAUS..223..483S
We report on a novel investigation of the complex magnetism of the
quiet Sun which is based on a realistic three-dimensional modeling of
the Hanle effect.
---------------------------------------------------------
Title: Chromospheric Magnetism and the Hanle Effect
Authors: Trujillo Bueno, J.
2003csss...12..196T Altcode:
This article shows how some recent developments in the observation and
theoretical modeling of weak polarization signals in chromospheric
spectral lines are facilitating fundamental new advances in our
ability to investigate the magnetism of the solar outer atmosphere
via spectropolarimetry.
---------------------------------------------------------
Title: Stellar granulation and the NLTE formation Žf the Fe I lines:
The metal-poor halo star HD 140283
Authors: Shchukina, N. G.; Trujillo Bueno, J.; Vasil'va, I.
2003KFNT...19..441S Altcode: 2003KFNT...19e.441S
The NLTE Fe I line formation problem in a three-dimensional granulation
model of the metal-poor halo star HD 140283 is considered. The
self-consistent solutions of the kinetic and radiative transfer
equations were obtained with a realistic atomic model Fe I + Fe II. The
effects of horizontal radiative transfer are neglected. The near-UV
overionisation effect is found to lead to sizeable Fe I opacity deficits
in the granular atmospheric regions. This NLTE effect tends to produce
weaker emergent spectral lines than in LTE because they are formed
deeper in the stellar granules where the source functions are close
to the Planck function. The NLTE effects in the integranule spectra
are small. If NLTE effects are shown to be fully taken into account
both in the three-dimensional and one-dimensional models of the star
HD 140283 the iron abundance is in close agreement for both cases.
---------------------------------------------------------
Title: Zero-Field Dichroism in the Solar Chromosphere
Authors: Manso Sainz, R.; Trujillo Bueno, J.
2003PhRvL..91k1102M Altcode: 2003astro.ph.11455M; 2003astro.ph.11455S; 2003PhRvL..91k1102S
We explain the linear polarization of the Ca ii infrared triplet
observed close to the edge of the solar disk. In particular, we
demonstrate that the physical origin of the enigmatic polarizations
of the 866.2 and 854.2nm lines lies in the existence of atomic
polarization in their metastable <SUP>2</SUP>D<SUP>3</SUP><SUB>/2 ,
5/2</SUB> lower levels, which produces differential absorption of
polarization components (dichroism). To this end, we have solved
the problem of the generation and transfer of polarized radiation by
taking fully into account all the relevant optical pumping mechanisms
in multilevel atomic models. We argue that “zero-field” dichroism
may be of great diagnostic value in astrophysics.
---------------------------------------------------------
Title: Quiet-Sun inter-network magnetic fields observed in the
infrared
Authors: Khomenko, E. V.; Collados, M.; Solanki, S. K.; Lagg, A.;
Trujillo Bueno, J.
2003A&A...408.1115K Altcode:
This paper presents the results of an investigation of the quiet Sun's
magnetic field based on high-resolution infrared spectropolarimetric
observations obtained with the Tenerife Infrared Polarimeter (TIP)
at the German VTT of the Observatorio del Teide. We observed two very
quiet regions at disc centre. The seeing was exceptionally good during
both observing runs, being excellent during one of them. In both cases
the network was intentionally avoided to the extent possible, to focus
the analysis on the characteristics of the weak polarization signals
of the inter-network regions. We find that the Stokes V profile of
Fe I 15648 Å line in almost 50% of the pixels and Stokes Q and/or
U in 20% of the pixels have a signal above 10<SUP>-3</SUP> (in units
of continuum intensity I<SUB>c</SUB>), which is significantly above
the noise level of 2-3 x 10<SUP>-4</SUP>. This implies that we detect
fluxes as low as 2 x 10<SUP>15</SUP> Mx/px. We find evidence that we
have detected most of the net flux that is in principle detectable at
1<SUP>”</SUP> resolution with the Zeeman effect. The observed linear
polarization resulting from the transverse Zeeman effect indicates that
the magnetic fields have a broad range of inclinations, although most
of the pixels show polarization signatures which imply an inclination
of about 20<SUP>o</SUP>. Nearly 30% of the selected V-profiles have
irregular shapes with 3 or more lobes, suggesting mixed polarities with
different LOS velocity within the resolution element. The profiles are
classified using a single value decomposition approach. The spatial
distribution of the magnetic signal shows that profiles of different
classes (having different velocities, splitting, asymmetries) are
clustered together and form patches, close to the spatial resolution
in size. Most of the field is found to be located in intergranular
lanes. The statistical properties of the mainly inter-network field
sampled by these observations are presented, showing that most of
the observed fields are weak with relatively few kG features. The
field strength distribution peaks at 350 G and has a FWHM of 300
G. Other parameters, such as profile asymmetries, filling factors and
line-of-sight velocities are also determined and discussed. <P />Based
on observations with the German Vacuum Tower Telescope (VTT) operated by
the Kiepenheuer-Institut für Sonnenphysik at the Spanish Observatorio
del Teide of the Instituto de Astrofísica de Canarias (IAC).
---------------------------------------------------------
Title: Nonequilibrium CO Chemistry in the Solar Atmosphere
Authors: Asensio Ramos, A.; Trujillo Bueno, J.; Carlsson, M.;
Cernicharo, J.
2003ApJ...588L..61A Altcode: 2003astro.ph..3460R; 2003astro.ph..3460A
Investigating the reliability of the assumption of instantaneous
chemical equilibrium (ICE) for calculating the CO number density in
the solar atmosphere is of crucial importance for the resolution of
the long-standing controversy over the existence of “cool clouds”
in the chromosphere and for determining whether the cool gas owes its
existence to CO radiative cooling or to a hydrodynamical process. Here
we report the first results of such an investigation in which we
have carried out time-dependent gas-phase chemistry calculations
in radiation hydrodynamical simulations of solar chromospheric
dynamics. We show that while the ICE approximation turns out to be
suitable for modeling the observed infrared CO lines at the solar disk
center, it may substantially overestimate the “heights of formation”
of strong CO lines synthesized close to the edge of the solar disk,
especially concerning vigorous dynamic cases resulting from relatively
strong photospheric disturbances. This happens because during the
cool phases of the hydrodynamical simulations, the CO number density
in the outer atmospheric regions is smaller than what is stipulated
by the ICE approximation, resulting in decreased CO opacity in the
solar chromosphere. As a result, the cool CO-bearing gas that produces
the observed molecular lines must be located at atmospheric heights
not greater than ~700 km. We conclude that taking into account the
nonequilibrium chemistry improves the agreement with the available
on-disk and off-limb observations but that the hydrodynamical simulation
model has to be even cooler than anticipated by the ICE approximation,
and this has to be the case at the “new” (i.e., deeper) formation
regions of the rovibrational CO lines.
---------------------------------------------------------
Title: Towards a Reliable Diagnostics of `Turbulent' Magnetic Fields
Via the Hanle Effect in the Sr I λ4607 Å Line
Authors: Shchukina, N.; Trujillo Bueno, J.
2003ASPC..307..336S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Radiative Transfer tools for the GTC
Authors: Asensio Ramos, A.; Trujillo Bueno, J.; Cernicharo, J.
2003RMxAC..16..162A Altcode:
We present very fast radiative transfer tools of interest for the
interpretation of future spectroscopic observations taken with the
GTC and its post-focus instrumentation. Our radiative transfer codes
are based on the iterative methods introduced by Trujillo Bueno &
Fabiani Bendicho (1995). Taking into consideration spherical geometry
and macroscopic velocity fields, we present results from the application
of these fast radiative transfer methods. We show why it is of interest
to develop a medium-high resolution spectrograph in order to be able
to resolve the rotational structure of the molecular bands. We show
some spectropolarimetric observations made with the Tenerife Infrared
Polarimeter (TIP), developed at the IAC and the theoretical modeling
done with the theoretical tools we have developed.
---------------------------------------------------------
Title: Non-equilibrium Chemistry and Molecular Spectropolarimetry
Authors: Asensio Ramos, A.; Trujillo Bueno, J.
2003ASPC..307..195A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: New Diagnostic Windows on the Weak Magnetism of the Solar
Atmosphere
Authors: Trujillo Bueno, J.
2003ASPC..307..407T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Multilevel Radiative Transfer Program for Modeling Scattering
Line Polarization and the Hanle Effect in Stellar Atmospheres
Authors: Manso Sainz, R.; Trujillo Bueno, J.
2003ASPC..307..251M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Radiative Transfer in Molecular Lines
Authors: Asensio Ramos, A.; Trujillo Bueno, J.
2003ASPC..288..335A Altcode: 2003sam..conf..335A
Molecular lines are generally very good tracers of the physical
conditions in cold regions of the Universe (e.g. molecular clouds,
cool stars, etc.), but molecular species are also found in not so
cold environments (e.g. the magnetized solar atmosphere). For a
reliable interpretation of spectroscopic and spectropolarimetric
observations of molecular lines it is often necessary to carry out
detailed radiative transfer simulations in molecular lines, both in
LTE and NLTE. Here we present a multilevel radiative transfer code for
the synthesis of molecular lines in stellar atmospheres, showing some
illustrations of calculations in different astrophysical contexts and
considering molecules like H<SUB>2O</SUB>, CO and OH. We will discuss
our implementation of highly convergent iterative methods and formal
solvers with especial emphasis on spherical geometry. We will also
present a chemical evolution code which is currently allowing us to
check the approximation of instantaneous chemical equilibrium in the
calculation of the abundances of a variety of molecular species.
---------------------------------------------------------
Title: Astrophysical Spectropolarimetry and Magnetic Field Diagnostics
Authors: Trujillo Bueno, J.
2003IAUS..210..243T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar Polarization
Authors: Trujillo-Bueno, Javier; Sanchez Almeida, Jorge
2003ASPC..307.....T Altcode: 2003sopo.conf.....T
No abstract at ADS
---------------------------------------------------------
Title: The Generation and Transfer of Polarized Radiation in Stellar
Atmospheres
Authors: Trujillo Bueno, J.
2003ASPC..288..551T Altcode: 2003sam..conf..551T
The standard Non-LTE problem consists in calculating the atomic
level populations that are consistent with the intensity of the
radiation field generated within any given stellar atmospheric
model. In contrast, the Non-LTE problem of the second kind is,
indeed, like an “algebraic Annapurna”: it requires to calculate
the diagonal and non-diagonal elements of the atomic density matrix
(associated to each level i of total angular momentum J<SUB>i</SUB>)
that are consistent with the intensity and polarization of the radiation
field generated within the (generally magnetized) stellar atmospheric
model under consideration. After arguing why this problem is of real
astrophysical interest, I will introduce the relevant equations and
the basic anisotropic radiation pumping processes. Finally, I will
show how to solve efficiently Non-LTE problems of the second kind via
the development and application of fast iterative methods and accurate
formal solvers of the Stokes vector transfer equation.
---------------------------------------------------------
Title: Non-LTE Determination of Iron and Oxygen Abundances Using 3D
Hydrodynamical Models: the Metal-Poor Star HD140283
Authors: Shchukina, N. G.; Vasiljeva, I. E.; Trujillo Bueno, J.;
Asplund, M.
2003IAUS..210P.B10S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Polarización en Astrofísica
Authors: Trujillo Bueno, J.
2003cnam.conf...10T Altcode:
Polarized light provides key information on the physical conditions
and geometry of astrophysical plasmas otherwise unattainable via
conventional spectroscopy. In particular, the remote sensing of
solar and stellar magnetic fields requires the measurement and
rigorous theoretical interpretation of polarization signals in
atomic and molecular lines, which are induced by various subtle
physical mechanisms. I will begin presenting a brief introduction to
“Astrophysical Spectropolarimetry”, emphasizing the importance of
developing diagnostic tools that take proper account of the Zeeman
Effect, optical pumping processes and the Hanle Effect. Only in this way
may we hope to investigate the strength and topology of stellar magnetic
fields in a parameter domain which ranges from at least milligauss to
many thousands of gauss. In the second part of the talk I will discuss
some interesting applications in solar magnetism, suggesting also what
type of collaborations between physicists and chemists could lead to
new advances in astrophysics.
---------------------------------------------------------
Title: New Spectropolarimetric Observations of Solar Coronal Filaments
in the He I 10830 Å Multiplet
Authors: Collados, M.; Trujillo Bueno, J.; Asensio Ramos, A.
2003ASPC..307..468C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Statistical properties of magnetic fields in intranetwork
Authors: Khomenko, E. V.; Collados, M.; Lagg, A.; Solanki, S. K.;
Trujillo Bueno, J.
2002ESASP.505..445K Altcode: 2002IAUCo.188..445K; 2002solm.conf..445K
We report a study of the quiet sun's magnetic field based
on high-resolution infrared spectropolarimetric observations
(TIP/VTT). We find that in almost 50% of the pixels Stokes V and in 15%
the Stokes Q and/or U profiles have a signal above 10<SUP>-3</SUP>. The
statistical properties of the mainly intranetwork field sampled by these
observations are presented, showing that most of the observed fields
are weak (the field strength distribution peaks at 350 G and has a FWHM
of 300 G) with very few kG features. The magnetized regions occupy a
very small fill fractions (about 2%). The field changes properties on
granular spatial scales and the size of the patches formed by similar
profiles is close to 1". Most of the parameters of the observed
polarization profiles show correlations with granulation parameters.
---------------------------------------------------------
Title: Remote sensing of chromospheric magnetic fields via the Hanle
and Zeeman effects
Authors: Trujillo Bueno, J.; Manso Sainz, R.
2002NCimC..25..783T Altcode: 2007arXiv0711.2584T
The only way to obtain reliable empirical information on the intensity
and topology of the weak magnetic fields of the quiet solar chromosphere
is via the measurement and rigorous physical interpretation of
polarization signals in chromospheric spectral lines. The observed
Stokes profiles reported here are due to the Hanle and Zeeman effects
operating in a weakly magnetized plasma that is in a state far from
local thermodynamic equilibrium. The physical origin of their enigmatic
linear polarization Q and U components is the existence of atomic
polarization in their metastable lower-levels, which permits the action
of a dichroism mechanism that has nothing to do with the transverse
Zeeman effect. It is also pointed out that the population imbalances
and coherences among the Zeeman sublevels of such long-lived atomic
levels can survive in the presence of horizontal magnetic fields having
intensities in the gauss range, and produce significant polarization
signals. Finally, it is shown how the most recent developments in the
observation and theoretical modelling of weak polarization signals are
facilitating fundamental new advances in our ability to investigate
the magnetism of the outer solar atmosphere via spectropolarimetry.
---------------------------------------------------------
Title: On the Atomic Polarization of the Ground Level of Na I
Authors: Casini, Roberto; Landi Degl'Innocenti, Egidio; Landolfi,
Marco; Trujillo Bueno, Javier
2002ApJ...573..864C Altcode: 2002astro.ph..4341C
In a recent Letter, we showed the remarkable result that the atomic
alignment of the levels P<SUB>1/2</SUB> and S<SUB>1/2</SUB> of the
D<SUB>1</SUB> line of Na I is practically destroyed in the presence of
magnetic fields sensibly larger than 10 G, irrespective of the field
direction. In this paper, we analytically demonstrate that this property
is a consequence of the decoupling of the electronic and nuclear angular
momenta J and I in the excited state P<SUB>3/2</SUB>, which is achieved
when the Zeeman splitting from the local magnetic field becomes much
larger than the typical hyperfine separation for that level.
---------------------------------------------------------
Title: The Physical Origin of the Scattering Polarization of the Na
I D Lines in the Presence of Weak Magnetic Fields
Authors: Trujillo Bueno, Javier; Casini, Roberto; Landolfi, Marco;
Landi Degl'Innocenti, Egidio
2002ApJ...566L..53T Altcode: 2002astro.ph..1389T
We demonstrate that the atomic alignment of the hyperfine-structure
components of the ground-level S<SUB>1/2</SUB> of Na I and of the
upper-level P<SUB>1/2</SUB> of the D<SUB>1</SUB> line are practically
negligible for magnetic strengths B>10 G and virtually zero
for B>~100 G. This occurs independently of the magnetic field
inclination on the stellar surface (also, in particular, for vertical
fields). Consequently, the characteristic antisymmetric linear
polarization signature of the scattered light in the D<SUB>1</SUB>
line is practically suppressed in the presence of magnetic fields
larger than 10 G, regardless of their inclination. Remarkably, we
find that the scattering polarization amplitude of the D<SUB>2</SUB>
line increases steadily with the magnetic strength, for vertical
fields above 10 G, while the contribution of the alignment to the
polarization of the D<SUB>1</SUB> line rapidly decreases. Therefore,
we suggest that spectropolarimetric observations of the “quiet”
solar chromosphere showing significant linear polarization peaks in
both D<SUB>1</SUB> and D<SUB>2</SUB> cannot be interpreted in terms
of one-component magnetic field models, implying that the magnetic
structuring of the solar chromosphere could be substantially more
complex than previously thought.
---------------------------------------------------------
Title: Selective absorption processes as the origin of puzzling
spectral line polarization from the Sun
Authors: Trujillo Bueno, J.; Landi Degl'Innocenti, E.; Collados, M.;
Merenda, L.; Manso Sainz, R.
2002Natur.415..403T Altcode: 2002astro.ph..1409T
Magnetic fields play a key role in most astrophysical systems, from
the Sun to active galactic nuclei. They can be studied through their
effects on atomic energy levels, which produce polarized spectral
lines. In particular, anisotropic radiation `pumping' processes (which
send electrons to higher atomic levels) induce population imbalances
that are modified by weak magnetic fields. Here we report peculiarly
polarized light in the HeI 10,830-Å multiplet observed in a coronal
filament located at the centre of the solar disk. We show that the
polarized light arises from selective absorption from the ground level
of the triplet system of helium, and that it implies the presence of
magnetic fields of the order of a few gauss that are highly inclined
with respect to the solar radius vector. This disproves the common
belief that population imbalances in long-lived atomic levels are
insignificant in the presence of inclined fields of the order of a few
gauss, and opens up a new diagnostic window for the investigation of
solar magnetic fields.
---------------------------------------------------------
Title: Astrophysical spectropolarimetry
Authors: Trujillo-Bueno, J.; Moreno-Insertis, F.; Sánchez, F.
2002apsp.conf.....T Altcode:
The polarization of light is the key to obtaining a wealth of essential
information that lies encoded in the electromagnetic radiation from
cosmic objects. Spectropolarimetry and imaging polarimetry provide
powerful diagnostics of the physical conditions in astrophysical
plasmas, which cannot be obtained via conventional spectroscopy. Whilst
its application to other fields of astrophysics is still at an early
stage of development, spectropolarimetry is being used with great
success in solar physics. The book contains the lectures delivered
at the XII Canary Islands Winter School of Astrophysics. Written by
eight prestigious astrophysics researchers, it covers the physics of
polarization, polarized radiation diagnostics of solar magnetic fields,
stellar magnetic fields, polarization insights for active galactic
nuclei, compact objects and accretion disks, astronomical masers and
their polarization, infrared-submillimeter spectropolarimetry, and
instrumentation for astrophysical spectropolarimetry. This timely volume
will provide graduate students and researchers with an unprecedented
introduction to the field of astrophysical spectropolarimetry.
---------------------------------------------------------
Title: Preface (Astrophysical spectropolarimetry)
Authors: Trujillo-Bueno, Javier; Moreno-Insertis, Fernando
2002apsp.confD..11T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Astrophysical Spectropolarimetry
Authors: Trujillo-Bueno, Javier; Moreno-Insertis, Fernando; Sanchez
Martinez, Francisco
2002assp.book.....T Altcode:
This book contains the lectures delivered at the XII Canary Islands
Winter School of Astrophysics on Astrophysical Spectropolarimetry. It
highlights how recent developments in theoretical astrophysics and
astronomical instrumentation are leading an ever-growing number of
astrophysicists to appreciate the enormous diagnostic potential offered
by spectropolarimetry.
---------------------------------------------------------
Title: Radiative transfer in molecular lines
Authors: Asensio Ramos, A.; Trujillo Bueno, J.; Cernicharo, J.
2001ESASP.460..265A Altcode: 2001astro.ph..2270R; 2001astro.ph..2270A; 2001phso.conf..265A
The highly convergent iterative methods developed by Trujillo Bueno
and Fabiani Bendicho (1995) for radiative transfer (RT) applications
are generalized to spherical symmetry with velocity fields. These RT
methods are based on Jacobi, Gauss-Seidel (GS), and SOR iteration
and they form the basis of a new NLTE multilevel transfer code for
atomic and molecular lines. The benchmark tests carried out so far are
presented and discussed. The main aim is to develop a number of powerful
RT tools for the theoretical interpretation of molecular spectra.
---------------------------------------------------------
Title: G-Band Spectral Synthesis in Solar Magnetic Concentrations
Authors: Sánchez Almeida, J.; Asensio Ramos, A.; Trujillo Bueno,
J.; Cernicharo, J.
2001ApJ...555..978S Altcode: 2001astro.ph..3006A; 2001astro.ph..3006S
Narrowband imaging in the G band is commonly used to trace the small
magnetic field concentrations of the Sun, although the mechanism that
makes them bright has remained unclear. We carry out LTE syntheses
of the G band in an assorted set of semiempirical model magnetic
concentrations. The syntheses include all CH lines as well as the main
atomic lines within the bandpass. The model atmospheres produce bright
G-band spectra having many properties in common with the observed G-band
bright points. In particular, the contrast referring to the quiet Sun
is about twice the contrast in continuum wavelengths. The agreement
with observations does not depend on the specificities of the model
atmosphere; rather, it holds from single flux tubes to microstructured
magnetic atmospheres. However, the agreement requires that the real
G-band bright points are not spatially resolved, even in the best
observations. Since the predicted G-band intensities exceed by far
the observed values, we foresee a notable increase of contrast of the
G-band images upon improvement of the angular resolution. According
to the LTE modeling, the G-band spectrum emerges from the deep
photosphere that produces the continuum. Our syntheses also predict
solar magnetic concentrations showing up in continuum images but
not in the G band. Finally, we have examined the importance of the
CH photodissociation in setting the amount of G-band absorption. It
turns out to play a minor role.
---------------------------------------------------------
Title: Radiative Transfer for the FIRST ERA
Authors: Trujillo Bueno, J.
2001ESASP.460..261T Altcode: 2001astro.ph..2269B; 2001astro.ph..2269T; 2001phso.conf..261T
This paper presents a brief overview of some recent advances in
numerical radiative transfer, which may help the molecular astrophysics
community to achieve new breakthroughs in the interpretation of
spectro-(polarimetric) observations.
---------------------------------------------------------
Title: A Time-dependent Semiempirical Model of the Chromospheric
Umbral Oscillation
Authors: Socas-Navarro, H.; Trujillo Bueno, J.; Ruiz Cobo, B.
2001ApJ...550.1102S Altcode:
We present a time-dependent semiempirical model of the chromospheric
umbral oscillation in sunspots. This model has been obtained by
applying recently developed non-LTE inversion techniques to a time
series of spectropolarimetric observations. The model consists of
two optically thick unresolved atmospheric components: a “quiet”
component with downward velocities that covers most of the resolution
element and an “active” component with upward velocities as high as 10
km s<SUP>-1</SUP> that covers a smaller filling factor and has a higher
temperature at the same chromospheric optical depth. This semiempirical
model accounts for all the observational signatures of the chromospheric
oscillation when the filling factor of the active component oscillates
between a few percent and 20% of the resolution element. We discuss
a plausible physical scenario in which upward-propagating waves in
a downflowing magnetized environment lead to periodic mass ejections
from the atmospheric layers where the waves become nonlinear. Based
on observations obtained with the Gregory Coudé Telescope, operated
on the island of Tenerife by the Observatory of Göttingen University
in the Spanish Observatorio del Teide of the Instituto de Astrofísica
de Canarias.
---------------------------------------------------------
Title: The Iron Line Formation Problem in Three-dimensional
Hydrodynamic Models of Solar-like Photospheres
Authors: Shchukina, Nataliya; Trujillo Bueno, Javier
2001ApJ...550..970S Altcode:
This paper presents the results of a detailed theoretical investigation
of the iron line formation NLTE problem in a three-dimensional model
of the solar photosphere, which we have obtained from a very recent
radiation hydrodynamics simulation of solar surface convection. In
this first paper we have neglected the effects of horizontal radiative
transfer on the atomic level populations, but we have considered a
realistic atomic model for iron that contains hundreds of radiative
transitions from the UV to the IR. The self-consistent solutions
of the kinetic and transfer equations have been obtained with a new
NLTE code, which is based on very efficient iterative methods. We find
that overionization due to the near-UV radiation field does take place
but mainly in the granular atmospheric regions. This well-known NLTE
mechanism tends to produce underpopulation of all the Fe I levels
and a very small overexcitation of the Fe II levels. All over the
three-dimensional photospheric model Fe II is the dominant ionization
stage. We find significant LTE versus NLTE discrepancies mainly for
the low-excitation Fe I lines. This applies to both the vertically
emergent profiles from the granular regions and also to the spatially
averaged profiles. These discrepancies are due to the line opacity
deficits that result from the aforementioned underpopulation of the
Fe I levels. The emergent profiles of the low-excitation lines of Fe I
are thus weaker in NLTE than in LTE. In particular, the largest errors
in the equivalent widths (due to the LTE assumption) are found for
the weakest low-excitation lines of Fe I. We also give quantitative
estimates of the errors in the temperature structure of semiempirical
solar granulation models obtained via the application of LTE inversion
techniques to several groups of Fe I lines. For instance, the widely
used Fe I 6301 and 6302 Å lines tend to lead to an overestimation of
about 100-200 K in the granular regions but to a similar underestimation
in the intergranular plasma. The present paper considers also the
case of the Sun observed with low spatial resolution, with particular
emphasis on the long-standing iron abundance problem. We show that it is
possible to obtain a very good fit to the observed spectral line shapes
by slightly changing the iron abundance (for both the LTE and NLTE
cases). In general, the iron abundance we need for reaching the best
NLTE fit to observed equivalent widths is 0.074+/-0.03 dex larger than
that needed to obtain the best LTE fit. Our most relevant conclusion
with regard to the solar iron abundance issue is the following: if NLTE
effects are fully taken into account in the three-dimensional model of
the solar photosphere, we obtain the meteoritic iron abundance value
(A<SUB>Fe</SUB>=7.50). However, if the abundance analysis is done
assuming LTE, we find A<SUB>Fe</SUB>=7.43, in close agreement with
the recent LTE analysis of Asplund and collaborators. Our results do
indicate that NLTE effects are significant but not above the 0.1 dex
level in the Sun. We consider our NLTE result for the iron abundance as
an additional hint of the realism of such three-dimensional hydrodynamic
simulations. We conclude that the success of the LTE fitting approach
is no proof that NLTE effects are negligible because the existing NLTE
effects are compensated for in the LTE analysis by a change in the
derived iron abundance. The paper ends emphasizing the great importance
of a full three-dimensional NLTE approach in order to be able to lead
to new advances in the field of quantitative stellar spectroscopy and,
in particular, for a correct derivation of elemental abundance ratios
in the atmospheres of metal-poor stars.
---------------------------------------------------------
Title: Fe I Lines in the Spectra of Solar-like Stars: NLTE Effects,
Temperature Diagnostics and the Iron Abundance (CD-ROM Directory:
contribs/shchukin)
Authors: Shchukina, N. G.; Trujillo Bueno, J.
2001ASPC..223..868S Altcode: 2001csss...11..868S
No abstract at ADS
---------------------------------------------------------
Title: Atomic Polarization and the Hanle Effect
Authors: Trujillo Bueno, J.
2001ASPC..236..161T Altcode: 2001aspt.conf..161T; 2002astro.ph..2328T
This article presents an introduction to optical pumping, atomic
polarization and the Hanle effect in weakly magnetized stellar
atmospheres. Although the physical processes and the theoretical
framework described here are of interest for applications in a
variety of astrophysical contexts (e.g. scattering polarization in
circumstellar envelopes and polarization in astronomical masers), the
article focuses mainly on the quest for understanding the physical
origin of the linearly polarized solar limb spectrum. It considers
also the development of the Hanle effect as a reliable diagnostic
tool for making feasible new advances in solar photospheric and
chromospheric magnetism. Particular emphasis is given to a rigorous
modeling of polarization phenomena as the essential link between theory
and observations. Some of the most recent advances in this field
are presented after carefully explaining how the various radiation
pumping mechanisms lead to atomic polarization in the absence and in
the presence of weak magnetic fields.
---------------------------------------------------------
Title: Full Stokes LPSP Observations of the Na D<SUB>1</SUB> and
D<SUB>2</SUB> Lines in Magnetized Regions close to the Solar Limb
Authors: Martínez Pillet, V.; Trujillo Bueno, J.; Collados, M.
2001ASPC..236..133M Altcode: 2001aspt.conf..133M
No abstract at ADS
---------------------------------------------------------
Title: Metastable-level Atomic Polarization and the Diagnostic
Problem of Chromospheric Magnetic Fields
Authors: Trujillo Bueno, J.; Manso Sainz, R.
2001ASPC..248...83T Altcode: 2001mfah.conf...83T
No abstract at ADS
---------------------------------------------------------
Title: THÉMIS Observations of the Second Solar Spectrum
Authors: Trujillo Bueno, J.; Collados, M.; Paletou, F.; Molodij, G.
2001ASPC..236..141T Altcode: 2001aspt.conf..141T
No abstract at ADS
---------------------------------------------------------
Title: Modeling the Scattering Line Polarization of the Ca II
Infrared Triplet
Authors: Manso Sainz, R.; Trujillo Bueno, J.
2001ASPC..236..213M Altcode: 2001aspt.conf..213M
No abstract at ADS
---------------------------------------------------------
Title: Scattering Polarization Observations with the Tenerife Gregory
Coudé Telescope
Authors: Dittmann, O.; Trujillo Bueno, J.; Semel, M.; López Ariste, A.
2001ASPC..236..125D Altcode: 2001aspt.conf..125D
No abstract at ADS
---------------------------------------------------------
Title: Anomalous Circular Polarization Profiles in Sunspot
Chromospheres
Authors: Socas-Navarro, H.; Trujillo Bueno, J.; Ruiz Cobo, B.
2000ApJ...544.1141S Altcode:
This paper presents a detailed description, analysis, and
interpretation of the spectropolarimetric observations recently
reported by Socas-Navarro, Trujillo Bueno, & Ruiz Cobo. These
observations consist of time series of Stokes I and V profiles above a
sunspot umbra. The spectral lines observed simultaneously are the Ca II
chromospheric lines at 8498 and 8542 Å and the photospheric Fe I line
at 8497 Å. These spectropolarimetric observations unveil an intriguing
time-dependent behavior of the Stokes V profiles in the chromospheric
lines. This behavior should be considered as an observational reference
for future radiation magnetohydrodynamic simulations of sunspot
chromospheres. The analysis of the observed time series shows that a
“normal,” nearly antisymmetric V profile rapidly evolves toward an
“anomalous,” completely asymmetric profile, returning later to the
normal state. The occurrence of such anomalous circular polarization
profiles repeats itself with a periodicity of ~150 s. After giving
arguments to discard other scenarios, we are able to interpret the
anomalous V profiles as a consequence of the development of a second
unresolved atmospheric component. This unresolved component seems to be
the same that produces the umbral flashes observed in other sunspots,
where it is present with a larger filling factor. Based on observations
obtained with the Gregory Coudé Telescope, operated on the island of
Tenerife by the Observatory of Göttingen University, in the Spanish
Observatorio del Teide of the Instituto de Astrofísica de Canarias.
---------------------------------------------------------
Title: Anomalous Polarization Profiles in Sunspots: Possible Origin
of Umbral Flashes
Authors: Socas-Navarro, H.; Trujillo Bueno, J.; Ruiz Cobo, B.
2000Sci...288.1396S Altcode: 2000Sci...288.1398S
We present time-series spectropolarimetric observations of sunspots
in the Ca II infrared triplet lines, which show a periodic occurrence
of anomalous, asymmetric, circular polarization profiles in the umbral
chromosphere. The profiles may be caused by the periodic development of
an unresolved atmospheric component in a downward flowing magnetized
environment. This active component with upward directed velocities
as high as 10 kilometers per second is connected to the umbral flash
(UF) phenomenon. We can explain the observations with a semiempirical
model of the chromospheric oscillation and of the sunspot magnetized
atmospheric plasma during a UF event.
---------------------------------------------------------
Title: Non-LTE Inversion of Stokes Profiles Induced by the Zeeman
Effect
Authors: Socas-Navarro, H.; Trujillo Bueno, J.; Ruiz Cobo, B.
2000ApJ...530..977S Altcode:
This paper presents a new diagnostic tool for the inference of the
thermal, dynamic, and magnetic properties of the solar chromosphere. It
consists of a non-LTE inversion code of Stokes profiles induced by
the Zeeman effect in magnetized stellar atmospheres. This code is the
generalization, to the non-LTE Stokes transfer case, of the inversion
code for unpolarized line profiles of Socas-Navarro, Ruiz Cobo, &
Trujillo Bueno. It is based upon a full non-LTE multilevel treatment
of Zeeman line transfer in which the thermal, magnetic, and dynamic
properties of the atmospheric model are adjusted automatically by
means of nonlinear least-squares-fitting techniques until a best fit
to the observed Stokes profiles is obtained. Our non-LTE inversion
approach is based on the concept of response functions, which measure
the emergent Stokes profiles' first-order reaction to changes in the
atmospheric parameters. We generalize our fixed departure coefficients
(FDC) approximation in order to allow fast computation of such response
functions in the present non-LTE Zeeman line transfer context. We
present several numerical tests showing the reliability of our inversion
method for retrieving the information about the thermodynamics and
the magnetic field vector that is contained in the polarization
state of the chosen spectral lines. We also explore the limitations
of the inversion code by applying it to simulated observations where
the physical hypotheses on which it is based on are not met. Finally,
we apply our non-LTE Stokes inversion code to real spectropolarimetric
observations of a sunspot observed in the IR triplet lines of Ca II. As
a result, a new mean model of the sunspot chromosphere is provided.
---------------------------------------------------------
Title: Radiative Transfer in Weakly Polarizing Media
Authors: Sánchez Almeida, J.; Trujillo Bueno, J.
1999ApJ...526.1013S Altcode:
We study radiative transfer through a weakly polarizing medium,
i.e., a medium in which the degree of polarization of the absorbed,
retarded, and emitted light is always weak. In this case, the general
radiative transfer equation for the Stokes parameters yields very simple
formal solutions. The intensity does not depend on the polarization,
and the other Stokes parameters are uncoupled from each other. It is
shown how this simplified radiative transfer equation holds in many
realistic cases relevant for solar and stellar magnetometry. It can be
applied whenever the weak magnetic field approximation works, i.e.,
for weakly split lines. In addition, it handles weak spectral lines,
structures with complex magnetic topology, chromospheric lines formed
under non-LTE conditions, etc. The merits of the approximation, which we
call the weakly polarizing medium (WPM) approximation, are illustrated
by means of several LTE and non-LTE line syntheses in realistic solar
model atmospheres. The WPM approximation should be useful in planning
and understanding measurements based on polarization. It simplifies
the relationship between the observed polarization and the physical
structure that one tries to retrieve. The approximation may also be
used in numerical problems requiring extensive polarized radiative
transfer (inversion codes, syntheses of stellar spectra, self-consistent
multilevel non-LTE Zeeman line transfer with atomic polarization, etc.).
---------------------------------------------------------
Title: Iterative Methods for the Non-LTE Transfer of Polarized
Radiation: Resonance Line Polarization in One-dimensional Atmospheres
Authors: Trujillo Bueno, Javier; Manso Sainz, Rafael
1999ApJ...516..436T Altcode:
This paper shows how to generalize to non-LTE polarization transfer some
operator splitting methods that were originally developed for solving
unpolarized transfer problems. These are the Jacobi-based accelerated
Λ-iteration (ALI) method of Olson, Auer, & Buchler and the
iterative schemes based on Gauss-Seidel and successive overrelaxation
(SOR) iteration of Trujillo Bueno and Fabiani Bendicho. The theoretical
framework chosen for the formulation of polarization transfer problems
is the quantum electrodynamics (QED) theory of Landi Degl'Innocenti,
which specifies the excitation state of the atoms in terms of the
irreducible tensor components of the atomic density matrix. This
first paper establishes the grounds of our numerical approach
to non-LTE polarization transfer by concentrating on the standard
case of scattering line polarization in a gas of two-level atoms,
including the Hanle effect due to a weak microturbulent and isotropic
magnetic field. We begin demonstrating that the well-known Λ-iteration
method leads to the self-consistent solution of this type of problem
if one initializes using the “exact” solution corresponding to
the unpolarized case. We show then how the above-mentioned splitting
methods can be easily derived from this simple Λ-iteration scheme. We
show that our SOR method is 10 times faster than the Jacobi-based ALI
method, while our implementation of the Gauss-Seidel method is 4 times
faster. These iterative schemes lead to the self-consistent solution
independently of the chosen initialization. The convergence rate of
these iterative methods is very high; they do not require either the
construction or the inversion of any matrix, and the computing time
per iteration is similar to that of the Λ-iteration method.
---------------------------------------------------------
Title: A new diagnostic tool for the solar chromosphere
Authors: Socas-Navarro, H.; Trujillo Bueno, J.; Ruiz Cobo, B.
1999ASSL..243..263S Altcode: 1999sopo.conf..263S
No abstract at ADS
---------------------------------------------------------
Title: The Hanle effect in 1D, 2D and 3D
Authors: Manso Sainz, R.; Trujillo-Bueno, J.
1999ASSL..243..143M Altcode: 2007arXiv0710.5430M; 1999sopo.conf..143M
This paper addresses the problem of scattering line polarization
and the Hanle effect in one-dimensional (1D), two-dimensional (2D)
and three-dimensional (3D) media for the case of a two-level model
atom without lower-level polarization and assuming complete frequency
redistribution. The theoretical framework chosen for its formulation
is the QED theory of Landi Degl'Innocenti (1983), which specifies
the excitation state of the atoms in terms of the irreducible tensor
components of the atomic density matrix. The self-consistent values of
these density-matrix elements is to be determined by solving jointly the
kinetic and radiative transfer equations for the Stokes parameters. We
show how to achieve this by generalizing to Non-LTE polarization
transfer the Jacobi-based ALI method of Olson et al. (1986) and the
iterative schemes based on Gauss-Seidel iteration of Trujillo Bueno
and Fabiani Bendicho (1995). These methods essentially maintain the
simplicity of the Lambda-iteration method, but their convergence rate is
extremely high. Finally, some 1D and 2D model calculations are presented
that illustrate the effect of horizontal atmospheric inhomogeneities
on magnetic and non-magnetic resonance line polarization signals.
---------------------------------------------------------
Title: Three-dimensional radiative transfer with multilevel atoms
Authors: Fabiani Bendicho, P.; Trujillo Bueno, J.
1999ASSL..243..219F Altcode: 1999sopo.conf..219F
No abstract at ADS
---------------------------------------------------------
Title: Towards the modelling of the second solar spectrum
Authors: Trujillo Bueno, J.
1999ASSL..243...73T Altcode: 1999sopo.conf...73T
No abstract at ADS
---------------------------------------------------------
Title: Non-LTE Inversion of Line Profiles
Authors: Socas-Navarro, H.; Ruiz Cobo, B.; Trujillo Bueno, J.
1998ApJ...507..470S Altcode:
In this paper we address the problem of the non-LTE (NLTE) inversion
of line profiles by means of a nonlinear least-squares minimization
procedure combined with very efficient multilevel transfer methods. Our
approach is based on the concept of response functions, which measure
the first-order response of the emergent profiles to changes in the
atmospheric conditions. We introduce the fixed departure coefficients
(FDC) approximation in order to compute these response functions in
a fast and straightforward manner. The accuracy of this approximation
is checked comparing FDC response functions with those obtained from
full NLTE computations. An NLTE inversion code based on these response
functions has been developed and extensively tested. Reference synthetic
profiles, similar to those expected from real observations, are given
as input to the inversion algorithm and the recovered models are shown
to be compatible with the reference models within the error bars. Our
NLTE inversion code thus provides a new tool for the investigation of
the chromospheres of the Sun and other stars.
---------------------------------------------------------
Title: Fe I lines in spectra of cool stars: NLTE effects in solar-like
atmosphere.
Authors: Shchukina, N. G.; Trujillo Bueno, J.
1998KFNT...14..315S Altcode: 1998KNFT...14..315S
A detailed NLTE investigation of Fe I lines is carried out for the
MACKKL quiet solar atmospheric model using a very realistic iron atomic
model. This improved atomic model consists of about 250 multiplets and
nearly 500 UV, optical and IR bound-bound and bound-free transitions
including the regime near the Fe I continuum. The authors find and
discuss some interesting statistical regularities with respect to
the errors found for the heights of formation, source functions,
equivalent widths and the central depths of the Fe I lines when the
LTE approximation is adopted.
---------------------------------------------------------
Title: Fe I lines in the spectra of cool stars: NLTE effects in
solar-like atmospheres.
Authors: Shchukina, N. G.; Trujillo Bueno, J.
1998KPCB...14..242S Altcode:
A detailed NLTE investigation of Fe I lines is carried out within
the framework of the MACKKL model of the quiet solar atmosphere. The
authors used a realistic iron atom model which allows for the fine
term structure and has about 250 levels; it involves nearly 500 UV,
optical, and IR bound-bound and bound-free transitions and includes the
conditions near the Fe I continuum. Errors that arise in the heights
of formation, source functions, equivalent widths, and central depths
of the Fe I lines within the LTE approximation are statistically
studied. The authors demonstrate that the behavior of the errors can
be described by a parametric set of curves depending on height of
line formation, the parameter being the excitation potential of the
lower level.
---------------------------------------------------------
Title: Diagnostic of the solar atmosphere using iron lines.
Authors: Shchukina, N. S.; Kostyk, R. I.; Trujillo Bueno, J.
1998IBUAA..12Q..32S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: NLTE effects in iron spectrum of sunspots.
Authors: Shchukina, N. G.; Trujillo Bueno, J.
1998IBUAA..12R..32S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Linearization versus Preconditioning: Which Approach Is Best
for Solving Multilevel Transfer Problems?
Authors: Socas-Navarro, H.; Trujillo Bueno, J.
1997ApJ...490..383S Altcode:
We present a critical analysis of linearization and preconditioning, the
two most used approaches proposed for achieving the required linearity
in the iterative solution of the multilevel transfer problem. By
distinguishing from the outset between the response of the radiation
field to the source function and opacity perturbations, we are able
to demonstrate that if the linearization strategy, on which the local
approximate Λ-operator option of the multilevel transfer code MULTI
is based, is applied neglecting the terms coming from the response of
the radiation field to the opacity perturbations, one then recovers the
same equations obtained using the preconditioning technique of Rybicki
& Hummer. It is also shown that if this preconditioning technique
is applied taking into account the response of the radiation field
to both the source function and opacity variations, one then ends up
with the same equations found via the linearization method. Thus these
two approaches to the numerical solution of the multilevel transfer
problem turn out to be essentially the same, because similar equations
are obtained if the same information is taken into account. Finally,
it is pointed out that, if one wishes to guarantee positivity for
the atomic level populations, it is necessary to neglect the terms
associated with the response of the radiation field to the opacity
perturbations. Neglecting such terms does not deteriorate the
convergence rate of multilevel transfer methods that make use of a
local approximate operator.
---------------------------------------------------------
Title: Multidimensional radiative transfer with multilevel
atoms. II. The non-linear multigrid method.
Authors: Fabiani Bendicho, P.; Trujillo Bueno, J.; Auer, L.
1997A&A...324..161F Altcode:
A new iterative method for solving non-LTE multilevel radiative
transfer (RT) problems in 1D, 2D or 3D geometries is presented. The
scheme obtains the self-consistent solution of the kinetic and
RT equations at the cost of only a few (<10) formal solutions
of the RT equation. It combines, for the first time, non-linear
multigrid iteration (Brandt, 1977, Math. Comp. 31, 333; Hackbush,
1985, Multi-Grid Methods and Applications, springer-Verlag, Berlin),
an efficient multilevel RT scheme based on Gauss-Seidel iterations
(cf. Trujillo Bueno & Fabiani Bendicho, 1995ApJ...455..646T),
and accurate short-characteristics formal solution techniques. By
combining a valid stopping criterion with a nested-grid strategy
a converged solution with the desired true error is automatically
guaranteed. Contrary to the current operator splitting methods the very
high convergence speed of the new RT method does not deteriorate when
the grid spatial resolution is increased. With this non-linear multigrid
method non-LTE problems discretized on N grid points are solved in O(N)
operations. The nested multigrid RT method presented here is, thus,
particularly attractive in complicated multilevel transfer problems
where small grid-sizes are required. The properties of the method are
analyzed both analytically and with illustrative multilevel calculations
for Ca II in 1D and 2D schematic model atmospheres.
---------------------------------------------------------
Title: The Limited Influence of Pressure Gradients on Late-Type
Stellar Line Asymmetries
Authors: Allende Prieto, Carlos; García López, Ramón J.; Trujillo
Bueno, Javier
1997ApJ...483..941A Altcode: 1997astro.ph..1061P; 1997astro.ph..1061A
Line asymmetries and shifts are powerful tools for studying velocity
fields in the stellar photospheres. Other effects, however, could
also generate asymmetries, blurring the information of the velocity
patterns. We have studied the shifts and asymmetries induced in the
profiles of spectral lines by pressure effects. The best theoretical and
experimental data on line broadening and shifts caused by collisions
with atomic hydrogen were used to analyze the Na I D and three Ca I
lines. Line bisectors of synthetic spectra computed with accurate data
for the Na I and Ca I lines are compared with very high resolution,
high signal-to-noise ratio solar spectra and indicate that pressure
broadening reproduces the wings of the observed lines, but pressure
shifts introduce neither asymmetries nor shifts comparable to the
observed ones.
---------------------------------------------------------
Title: Linear Polarization Due to Lower Level Depopulation Pumping
in Stellar Atmospheres
Authors: Trujillo Bueno, Javier; Landi Degl'Innocenti, Egidio
1997ApJ...482L.183T Altcode:
The possible generation of linear polarization in spectral lines due to
depopulation-pumping processes in stellar atmospheres is investigated
within the framework of a quantum electrodynamic theory for the
transfer of polarized radiation based on the atomic density-matrix
formalism. It is shown that the radiation field's anisotropy in
solar-like atmospheres induces population imbalances among the lower
level sublevels of optical line transitions. The depolarizing rates
that are assumed to model some typical spectral lines are not capable
of completely destroying such a lower level atomic alignment, and the
corresponding linear polarization signals are found to lie above the
sensitivity limit of some recently developed spectropolarimeters.
---------------------------------------------------------
Title: Are NLTE effects important for the inversion of iron lines?
Authors: Socas-Navarro, H.; Trujillo Bueno, J.; Ruiz Cobo, B.;
Shchukina, N. G.
1997joso.proc...86S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Is LTE a Suitable Approximation for Fe I - based Diagnostics
of the Thermal Structure of Sunspots?
Authors: Shchukina, N. G.; Trujillo Bueno, J.
1997ASPC..118..207S Altcode: 1997fasp.conf..207S
NLTE effects in iron lines are carefully investigated for the
sunspot umbral model of Maltby et. al. (1986). Our model atom is
realistic: it has hundreds of levels including many high-excited
ones among which infrared transitions take place. The self-consistent
solution of the kinetic and radiative transfer equations is obtained
using recently-developed multilevel transfer methods suitable for
efficiently handling hundreds of radiative transitions in detail
from the ultraviolet to the infrared. These NLTE multilevel transfer
calculations allow us to investigate whether the currently-used LTE
approximation is suitable for diagnosing the temperature structure of
sunspots via Fe I lines.
---------------------------------------------------------
Title: The Polarization-Free Approximation Applied to Multi-Level
Non-LTE Radiative Transfer
Authors: Bruls, J. H. M. J.; Trujillo Bueno, J.
1996SoPh..164..155B Altcode:
The polarization-free (POF) approximation (Trujillo Bueno and Landi
Degl'Innocenti, 1996) is capable of accounting for the approximate
influence of the magnetic field on the statistical equilibrium,
without actually solving the full Stokes vector radiative transfer
equation. The method introduces the Zeeman splitting or broadening
of the line absorption profile φI in the scalar radiative transfer
equation, but the coupling between Stokes I and the other Stokes
parameters is neglected. The expected influence of the magnetic field
is largest for strongly-split strong lines and the effect is greatly
enhanced by gradients in the magnetic field strength. Formally the
interaction with the other Stokes parameters may not be neglected for
strongly-split strong lines, but it turns out that the error in Stokes
I obtained through the POF approximation to a large extent cancels the
neglect of interaction with the other Stokes parameters, so that the
resulting line source functions and line opacities are more accurate
than those obtained with the field-free approach. Although its merits
have so far only been tested for a two-level atom, we apply the POF
approximation to multi-level non-LTE radiative transfer problems on
the premise that there is no essential difference between these two
cases. Final verification of its validity in multi-level cases still
awaits the completion of a non-LTE Stokes vector transfer code.
---------------------------------------------------------
Title: The polarization-free approximation
Authors: Trujillo Bueno, J.; Landi Degl'Innocenti, E.
1996SoPh..164..135T Altcode:
The development of effective iterative methods capable of accurately
solving NLTE Stokes transfer problems is of considerable importance
for the investigation of solar and stellar magnetic fields. After
briefly indicating the iterative approach which is being presently
pursued for the exact solution of such problems, the particular
regime where polarization signals can only be due to the Zeeman
effect is considered in some detail. By means of NLTE Stokes transfer
calculations for a two-level atomic model it is first shown that the
currently-used field-free approximation (Rees, 1969) cannot be safely
applied in the presence of magnetic field gradients. Such gradients
lead to changes in the shape and width of the line profiles and they
can produce non-negligible effects on the atomic level populations and
line source functions. A new approximate method is then proposed, which
does not require the actual solution of the Stokes vector transfer
equation and is practically as fast as the field-free one. This
polarization-free approximation provides a fairly good account of
the effects of homogeneous and inhomogeneous magnetic fields on the
statistical equilibrium and is very easy to implement in any existing
non-magnetic, multi-level transfer code.
---------------------------------------------------------
Title: A Novel Iterative Scheme for the Very Fast and Accurate
Solution of Non-LTE Radiative Transfer Problems
Authors: Trujillo Bueno, J.; Fabiani Bendicho, P.
1995ApJ...455..646T Altcode:
Iterative schemes based on Gauss-Seidel (G-S) and optimal successive
over-relaxation (SOR) iteration are shown to provide a dramatic
increase in the speed with which non-LTE radiation transfer (RT)
problems can be solved. The convergence rates of these new RT methods
are identical to those of upper triangular nonlocal approximate
operator splitting techniques, but the computing time per iteration
and the memory requirements are similar to those of a local operator
splitting method. In addition to these properties, both methods are
particularly suitable for multidimensional geometry, since they neither
require the actual construction of nonlocal approximate operators nor
the application of any matrix inversion procedure. <P />Compared with
the currently used Jacobi technique, which is based on the optimal
local approximate operator (see Olson, Auer, & Buchler 1986), the
G-S method presented here is faster by a factor 2. It gives excellent
smoothing of the high-frequency error components, which makes it the
iterative scheme of choice for multigrid radiative transfer. This
G-S method can also be suitably combined with standard acceleration
techniques to achieve even higher performance. <P />Although the
convergence rate of the optimal SOR scheme developed here for solving
non-LTE RT problems is much higher than G-S, the computing time per
iteration is also minimal, i.e., virtually identical to that of a local
operator splitting method. While the conventional optimal local operator
scheme provides the converged solution after a total CPU time (measured
in arbitrary units) approximately equal to the number n of points per
decade of optical depth, the time needed by this new method based on the
optimal SOR iterations is only √n/2√2. This method is competitive
with those that result from combining the above-mentioned Jacobi and
G-S schemes with the best acceleration techniques. <P />Contrary to
what happens with the local operator splitting strategy currently in
use, these novel methods remain effective even under extreme non-LTE
conditions in very fine grids.
---------------------------------------------------------
Title: Multidimensional radiative transfer with multilevel
atoms. I. ALI method with preconditioning of the rate equations.
Authors: Auer, L.; Bendicho, P. Fabiani; Trujillo Bueno, J.
1994A&A...292..599A Altcode:
We combine a number of powerful mathematical techniques to produce
an effective method for treating multidimensional radiative transfer
problems in complex atomic models without assuming LTE. The approach
is so efficient that multilevel two-dimensional (2D) modeling can now
be performed with no more than a workstation. We employ Accelerated
Lambda Iteration (ALI) methods: accurate short characteristics for
the formal solution of the transfer equation with an efficient new
strategy for horizontal periodic boundary conditions, local approximate
{LAMBDA}-operators given by the diagonal of the exact operator,
methods to accelerate the convergence, and preconditioning of the rate
equations. Of particular interest is a simple grid-doubling strategy
which both rapidly finds the converged solution in very fine meshes
and also estimates the true error of that solution. The properties of
the method are described in detail with the help of 2D line-transfer
calculations with multilevel model atoms for Ca II and H. These
illustrative multilevel calculations in schematic inhomogeneous
atmospheres demonstrate the importance of properly including the
effects of horizontal radiative transfer and realistic atomic models.
---------------------------------------------------------
Title: On photospheric flows and chromospheric corks
Authors: Brandt, P. N.; Rutten, R. J.; Shine, R. A.; Trujillo Bueno, J.
1994ASIC..433..251B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Multi-dimensional radiative transfer with multi-level atoms
and the diagnostic problem of small-scale structures
Authors: Trujillo Bueno, J.; Fabiani, P.; Auer, L.
1994smf..conf..328T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Atomic orientation in chromospheric lines.
Authors: Trujillo Bueno, J.; Martínez Pillet, V.; Sánchez Almeida,
J.; Landi Degl'Innocenti, E.
1993ASPC...46..526T Altcode: 1993ASPC...46..526B; 1993mvfs.conf..526T; 1993IAUCo.141..526T
Observations of the Stokes I and V profiles of the Ca II H and K lines
in solar magnetic regions are presented. Least-squares fits of dI/dλ
to V are obtained and the wavelength variation of the residuals,
i.e. V-kdI/dλ, calculated. The authors find significant symmetric
residuals in umbrae, which are in agreement with the effect on the
V profiles due to atomic orientation, i.e. with the existence of an
unequal population of the Zeeman sublevels with M > 0 with respect
to those with M < 0.
---------------------------------------------------------
Title: On the photospheric temperature in small-scale magnetic flux
concentrations
Authors: Fabiani Bendicho, P.; Kneer, F.; Trujillo Bueno, J.
1992A&A...264..229F Altcode:
Results are presented of 2D radiative transfer calculations performed
for geometric configurations that simulate partly evacuated
small-scale magnetic flux sheets embedded in the ambient solar
atmosphere. Temperature distributions in (gray) radiative equilibrium
at low optical depths where radiation transfer dominates the energy
budget are obtained. Two-dimensional radiative equilibrium flux
sheet models are calculated using a novel method which shows that the
temperature enhancement of the upper layers of photospheric magnetic
flux concentrations is due to the radiation channeling effect, i.e.,
that horizontal radiative transfer tends to channel emerging radiation
into the lower opacity regions. The walls of the flux sheets are found
to radiate energy from subphotospheric surrounding layers, giving rise
to a strong heating of the atmosphere of the flux sheets. Radiative
energy migrates horizontally from the heated flux sheets towards the
ambient medium and there it heats the atmosphere at low optical depths.
---------------------------------------------------------
Title: Dynamics of the Quiet Solar Atmosphere: K2v Cell Grains Versus
Magnetic Elements
Authors: Brandt, P. N.; Rutten, R. J.; Shine, R. A.; Trujillo Bueno, J.
1992ASPC...26..161B Altcode: 1992csss....7..161B
No abstract at ADS
---------------------------------------------------------
Title: On the Influence of Multi-Dimensional Radiative Transfer on
the Energetic Contribution of the CAK Line
Authors: Fabiani, P.; Trujillo-Bueno, J.
1991ASIC..341..423F Altcode: 1991sabc.conf..423F
No abstract at ADS
---------------------------------------------------------
Title: Do We Really Know What the Actual Chromospheric Heating
Requirements Are? (With 1 Figure)
Authors: Trujillo Bueno, J.
1991mcch.conf...60T Altcode:
No abstract at ADS
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Title: Multidimensional radiative transfer in stratified
atmospheres. VI - Radiative instabilities
Authors: Trujillo Bueno, J.; Kneer, F.
1990A&A...232..135T Altcode:
The possibility that radiative instabilities in stellar atmospheres
are driven by transfer of energy processes between stellar gas and the
radiation field is considered. Harmonic temperature fluctuations in
gray radiative equilibrium atmospheres are introduced, and the linear
response of the radiation field to the ensuing Planck-function and
opacity fluctuations is investigated. Analytical and numerical
calculations are performed, emphasizing the influence of the
multidimensional radiative transfer (MRT) effects of opacity
fluctuations on the radiative relaxation time as a function of the
wavenumber of the perturbations. Quantitative examples are given
for stellar atmospheres with solarlike T(eff) and gravitational
stratification. It is concluded that, while the MRT effects of
B fluctuations generally tend to be stabilizing, the MRT effects
of chi fluctuations are optically important for driving radiative
instabilities.
---------------------------------------------------------
Title: Radiative transfer problems in the Solar and Sun-like
atmospheres
Authors: Trujillo Bueno, J.
1990nwus.book..119T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Influence of Opacity Fluctuations on the Energy Transfer
by Radiation
Authors: Trujillo-Bueno, J.; Kneer, F.
1989ASIC..263..441T Altcode: 1989ssg..conf..441T
No abstract at ADS
---------------------------------------------------------
Title: On the κ-mechanism and the multi-dimensional Eddington
approximation.
Authors: Trujillo Bueno, J.
1988ESASP.286...11T Altcode: 1988ssls.rept...11T
To consider the possibility of a κ-like overstability mechanism as
the driving force of solar modes of oscillation requires a theoretical
description of the interaction between the hydrodynamics of the motion
and the radiative energy transport. The aim of this paper is to answer
the question of whether or not the frequently-used multi-dimensional
Eddington approximation is suitable for such purposes. It is found that
Eddington's approximation is generally adequate for giving account of
the radiative damping effects of Planck function fluctuations, while
it is in gross disagreement with the exact results with respect to the
radiative transfer effects of opacity fluctuations. Therefore, it is
concluded that its use should be avoided, when investigating κ-like
excitation mechanisms for nonradial stellar modes of oscillation.
---------------------------------------------------------
Title: Multi-dimensional energy transfer by radiation in the solar
atmosphere
Authors: Trujillo Bueno, Javier
1988PhDT.........6T Altcode:
Both linear and nonlinear analysis are used to gain a better
understanding of the effects of multi-dimensional transfer of energy by
radiation in spatially structured stellar atmospheres. Information on
the radiative response of RE (radiative equilibrium) model atmospheres
to temperature fluctuations is obtained. Whether or not such perturbed
systems always return to their initial RE configurations is addressed
by investigation of the dependence of the radiative relaxation times
on the geometry and structural lengths of the perturbations, as well
as establishing the conditions under which radiative instabilities
can be possible.
---------------------------------------------------------
Title: Multidimensional radiative transfer in stratified atmospheres
Authors: Kneer, F.; Trujillo-Bueno, J.
1987A&A...183...91K Altcode:
Energy transport by radiation is an important contribution to the energy
budget in stellar atmospheric structures. In this paper, radiative
relaxation of small-scale structures is investigated. The authors
show in a linear analysis: (1) Already at structural lengths of 10
opacity scale heights, horizontal photon exchange is important for the
energy budget. (2) In atmospheric layers near continuum optical depth
τ<SUB>c</SUB> = 1 and below, the continuum absorption and emission
processes dominate the radiative relaxation. (3) Weak spectral lines or
lines with σ<SUB>l</SUB>ɛ ≤ 1 have little influence on the energy
exchange. (4) At large heights, transport in few spectral lines with
σ<SUB>l</SUB>ɛ very large 1 can compete with continuum processes.
---------------------------------------------------------
Title: Multidimensional radiative transfer in stratified
atmospheres. IV - Radiative cooling by LTE and non-LTE spectral lines
Authors: Trujillo-Bueno, J.; Kneer, F.
1987A&A...174..183T Altcode:
The question of efficiency of radiative energy losses in spectral
lines is addressed. In a semi-infinite atmosphere with constant
temperature, the total radiative energy loss (integrated over all
depths) in a spectral line without continuum is infinite, in both
LTE and non-LTE. Thus, only local energy balances may be considered
with such models. The authors give radiative cooling functions for
various non-LTE parameters and structural lengths of a two-dimensional
stratified atmosphere. At the surface, cooling is less efficient in
non-LTE than in LTE. At large optical depths, both become equal and
are non-negligible. In these layers horizontal transfer effects become
important for the energy balance.
---------------------------------------------------------
Title: Radiative Relaxation in Small Scale Structures
Authors: Trujillo-Bueno, J.; Kneer, F.
1987rfsm.conf..281T Altcode:
The authors discuss the effects of multidimensional radiative transfer
on the energy exchange by radiation in small-scale structures.
---------------------------------------------------------
Title: The visible helium spectrum of a white-light flare.
Authors: Lites, B. W.; Meidig, D. F.; Trujillo Bueno, J.
1986lasf.conf..101L Altcode: 1986lasf.symp..101L
Emission lines of neutral and ionized helium at visible wavelengths are
measured in the white-light flare of 24 April 1981. These intensities,
along with accompanying profiles, are presented for the purpose of
providing an observational basis for future radiative transfer models
of white-light flares. Absolute intensities, both peak and integrated,
are given for 14 lines of He I, and for the He II line at 4686 Å. The
authors compare intensities of these lines in the white-light emitting
region to intensities measured in a flare kernel that does not show
significant continuum emission. From this, they infer that the white
light emission arises from material at chromospheric temperatures,
and not from temperatures greater than about 20,000K. A search for
Stark-enhanced forbidden neighbors to the allowed He I lines in this
disk flare was unsuccessful.
---------------------------------------------------------
Title: Multidimensional Radiative Transfer in Stratified Atmospheres:
Radiative Cooling by LTE and non-LTE Spectral Lines
Authors: Trujillo-Bueno, J.; Kneer, F.
1986MitAG..67..304T Altcode:
A detailed paper has been submitted to Astron. Astrophys.
