manso-sainz

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Author name code: manso-sainz
ADS astronomy entries on 2022-09-14
author:"Manso Sainz, Rafael"

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Title: Warm ionized gas in the blue compact galaxy Haro 14 viewed by
MUSE. The diverse ionization mechanisms acting in low-mass starbursts
Authors: Cairós, L. M.; González-Pérez, J. N.; Weilbacher, P. M.;
Manso Sainz, R.
2022A&A...664A.144C Altcode: 2022arXiv220602754C
We investigate the warm ionized gas in the blue compact galaxy (BCG)
Haro 14 by means of integral field spectroscopic observations taken
with the Multi Unit Spectroscopic Explorer (MUSE) at the Very Large
Telescope. The large field of view of MUSE and its unprecedented
sensitivity enable observations of the galaxy nebular emission up
to large galactocentric distances, even in the important but very
faint [O I] λ6300 diagnostic line. This allowed us to trace the
ionized gas morphology and ionization structure of Haro 14 up to
kiloparsec scales and, for the first time, to accurately investigate
the excitation mechanism operating in the outskirts of a typical
BCG. The intensity and diagnostic maps reveal at least two highly
distinct components of ionized gas: the bright central regions,
mostly made of individual clumps, and a faint component which extends
up to kiloparsec scales and consists of widespread diffuse emission,
well-delineated filamentary structures, and faint knots. Noteworthy are
the two curvilinear filaments extending up to 2 and 2.3 kpc southwest,
which likely trace the edges of supergiant expanding bubbles driven
by galactic outflows. We find that while the central clumps in Haro
14 are H II-region complexes, the morphology and line ratios of the
whole low-surface-brightness component are not compatible with star
formation photoionization. In the spatially resolved emission-line-ratio
diagnostic diagrams, spaxels above the maximum starburst line form
the majority (∼75% and ∼50% in the diagnostic diagrams involving
[O I] and [S II] respectively). Moreover, our findings suggest that
more than one alternative mechanism is ionizing the outer galaxy
regions. The properties of the diffuse component are consistent with
ionization by diluted radiation and the large filaments and shells
are most probably shocked areas at the edge of bubbles. The mechanism
responsible for the ionization of the faint individual clumps observed
in the galaxy periphery is more difficult to assess. These clumps
could be the shocked debris of fragmented shells or regions where
star formation is proceeding under extreme conditions. Based on
observations made with ESO Telescopes at Paranal Observatory under
programme ID 60.A-9186(A).

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Title: Ultraviolet Spectropolarimetry: Investigating stellar magnetic
field diagnostics
Authors: Folsom, C. P.; Ignace, R.; Erba, C.; Casini, R.; del Pino
Alemán, T.; Gayley, K.; Hobbs, K.; Manso Sainz, R.; Neiner, C.;
Petit, V.; Shultz, M. E.; Wade, G. A.
2022arXiv220701865F Altcode:
Magnetic fields are important for stellar photospheres and
magnetospheres, influencing photospheric physics and sculpting stellar
winds. Observations of stellar magnetic fields are typically made in
the visible, although infrared observations are becoming common. Here
we consider the possibility of directly detecting magnetic fields at
ultraviolet (UV) wavelengths using high resolution spectropolarimetry,
specifically considering the capabilities of the proposed Polstar
mission. UV observations are particularly advantageous for studying wind
resonance lines not available in the visible, but they can also provide
many photospheric lines in hot stars. Detecting photospheric magnetic
fields using the Zeeman effect and Least Squares Deconvolution is
potentially more effective in the UV due to the much higher density
of strong lines. We investigate detecting magnetic fields in the
magnetosphere of a star using the Zeeman effect in wind lines, and
find that this could be detectable at high S/N in an O or B star
with a strong magnetic field. We consider detecting magnetic fields
using the Hanle effect in linear polarization, which is complementary
to the Zeeman effect, and could be more sensitive in photospheric
lines of rapid rotators. The Hanle effect can also be used to infer
circumstellar magnetism in winds. Detecting the Hanle effect requires
UV observations, and a multi-line approach is key for inferring
magnetic field properties. This demonstrates that high resolution
spectropolarimetry in the UV, and the proposed Polstar mission, has
the potential to greatly expand our ability to detect and characterize
magnetic fields in and around hot stars.

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Title: Polarimetric characterization of segmented mirrors
Authors: Pastor Yabar, A.; Asensio Ramos, A.; Manso Sainz, R.;
Collados, M.
2022ApOpt..61.4908P Altcode: 2022arXiv220514640P
We study the impact of the loss of axial symmetry around the optical
axis on the polarimetric properties of a telescope with segmented
primary mirror when each segment is present in a different aging
stage. The different oxidation stage of each segment as they are
substituted in time leads to non-negligible crosstalk terms. This
effect is wavelength dependent and it is mainly determined by the
properties of the reflecting material. For an aluminum coating, the
worst polarimetric behavior due to oxidation is found for the blue
part of the visible. Contrarily, dust -- as modeled in this work --
does not significantly change the polarimetric behavior of the optical
system . Depending on the telescope, there might be segment substitution
sequences that strongly attenuate this instrumental polarization.

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Title: MUSE observations of the blue compact dwarf galaxy Haro
14. Data analysis and first results on morphology and stellar
populations
Authors: Cairós, L. M.; González-Pérez, J. N.; Weilbacher, P. M.;
Manso Sainz, R.
2021A&A...654A.142C Altcode: 2021arXiv210809107C
Investigations of blue compact galaxies (BCGs) are essential to
advancing our understanding of galaxy formation and evolution. BCGs are
low-luminosity, low-metallicity, gas-rich objects that form stars at
extremely high rates, meaning they are good analogs to the high-redshift
star-forming galaxy population. Being low-mass starburst systems,
they also constitute excellent laboratories in which to investigate
the star formation process and the interplay between massive stars
and their surroundings. This work presents results from integral
field spectroscopic observations of the BCG Haro 14 taken with the
Multi Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope
in wide-field adaptive optics mode. The large MUSE field of view
(1'×1'; = 3.8 × 3.8 kpc2 at the adopted distance of 13
Mpc) enables simultaneous observations of the central starburst and
the low-surface-brightness host galaxy, which is a huge improvement
with respect to previous integral field spectroscopy of BCGs. From
these data we built galaxy maps in continuum and in the brightest
emission lines. We also generated synthetic broad-band images in the VRI
bands, from which we produced color index maps and surface brightness
profiles. We detected numerous clumps spread throughout the galaxy,
both in continuum and in emission lines, and produced a catalog with
their position, size, and photometry. This analysis allowed us to
study the morphology and stellar populations of Haro 14 in detail. The
stellar distribution shows a pronounced asymmetry; the intensity peak
in continuum is not centered with respect to the underlying stellar
host but is displaced by about 500 pc southwest. At the position of the
continuum peak we find a bright stellar cluster that with Mv
= −12.18 appears as a strong super stellar cluster candidate. We
also find a highly asymmetric, blue, but nonionizing stellar component
that occupies almost the whole eastern part of the galaxy. We conclude
that there are at least three different stellar populations in Haro 14:
the current starburst of about 6 Myr; an intermediate-age component of
between ten and several hundred million years; and a red and regular
host of several gigayears. The pronounced lopsidedness in the continuum
and also in the color maps, and the presence of numerous stellar
clusters, are consistent with a scenario of mergers or interactions
acting in Haro 14. Based on observations made with ESO Telescopes
at Paranal Observatory under programme ID 60.A-9186(A).

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Title: Solar Disk Center Shows Scattering Polarization in the Sr I
4607 Å Line
Authors: Zeuner, Franziska; Manso Sainz, Rafael; Feller, Alex; van
Noort, Michiel; Solanki, Sami K.; Iglesias, Francisco A.; Reardon,
Kevin; Martínez Pillet, Valentín
2020ApJ...893L..44Z Altcode: 2020arXiv200403679Z
Magnetic fields in turbulent, convective high-β plasma naturally
develop highly tangled and complex topologies - the solar photosphere
being the paradigmatic example. These fields are mostly undetectable by
standard diagnostic techniques with finite spatio-temporal resolution
due to cancellations of Zeeman polarization signals. Observations of
resonance scattering polarization have been considered to overcome
these problems. But up to now, observations of scattering polarization
lack the necessary combination of high sensitivity and high spatial
resolution in order to directly infer the turbulent magnetic structure
at the resolution limit of solar telescopes. Here, we report the
detection of clear spatial structuring of scattering polarization
in a magnetically quiet solar region at disk center in the Sr I
4607 Å spectral line on granular scales, confirming theoretical
expectations. We find that the linear polarization presents a
strong spatial correlation with the local quadrupole of the radiation
field. The result indicates that polarization survives the dynamic and
turbulent magnetic environment of the middle photosphere and is thereby
usable for spatially resolved Hanle observations. This is an important
step toward the long-sought goal of directly observing turbulent
solar magnetic fields at the resolution limit and investigating their
spatial structure.

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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.

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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.

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Title: Spectropolarimetry of the Solar Mg II h and k Lines
Authors: Manso Sainz, R.; del Pino Alemán, T.; Casini, R.; McIntosh,
S.
2019ApJ...883L..30M Altcode: 2019arXiv190905574M
We report on spectropolarimetric observations across the Mg II h and k
lines at 2800 Å made by the Ultraviolet Spectrometer and Polarimeter
on board the Solar Maximum Mission satellite. Our analysis confirms
the strong linear polarization in the wings of both lines observed
near the limb, as previously reported, but also demonstrates the
presence of a negatively (i.e., radially oriented) polarized signal
between the two lines. We find evidence for fluctuations of the
polarization pattern over a broad spectral range, resulting in some
depolarization with respect to the pure scattering case when observed
at very low spatial and temporal resolutions. This is consistent with
recent theoretical modeling that predicts this to be the result of
redistribution effects, quantum interference between the atomic levels
of the upper term, and magneto-optical effects. A first attempt at a
quantitative exploitation of these signals for the diagnosis of magnetic
fields in the chromosphere is attempted. In active regions, we present
observations of circular polarization dominated by the Zeeman effect. We
are able to constrain the magnetic field strength in the upper active
chromosphere using an analysis based on the magnetograph formula, as
justified by theoretical modeling. We inferred a significantly strong
magnetic field (∼500 G) at the 2.5σ level on an exceptionally active,
flaring region.

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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.

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Title: Magnetic Field Diagnostics with Strong Chromospheric Lines
Authors: Manso Sainz, R.; del Pino Alemán, T.; Casini, R.
2019ASPC..526..145M Altcode: 2017arXiv171004155M
The complex spectropolarimetric patterns around strong chromospheric
lines, the result of subtle spectroscopic and transport mechanisms,
are sensitive, sometimes in unexpected ways, to the presence of magnetic
fields in the chromosphere, which may be exploited for diagnostics. We
apply numerical polarization radiative transfer implementing partially
coherent scattering by polarized multi-term atoms, in the presence
of arbitrary magnetic fields, in plane-parallel stellar atmospheres
to study a few important spectroscopic features: Mg II h-k doublet;
Ca II H-K doublet and IR triplet. We confirm the importance of partial
redistribution effects in the formation of the Mg II h-k doublet in
magnetized atmospheres, as previously pointed out for the non-magnetic
case. Moreover, we show, numerically and analytically, that a magnetic
field produces measurable modifications of the broadband linear
polarization even for relatively small field strengths, while circular
polarization remains well represented by the magnetograph formula. We
note that this phenomenon has already (unknowingly) been observed by
UVSP/SMM, and the interest and possibility of its observation in stars
other than the Sun. The interplay between partial redistribution in the
H-K doublet of Ca II and metastable level polarization in its IR triplet
allow diagnosing the chromospheric magnetic field at different layers
and strengths. Our results suggest several new avenues to investigate
empirically the magnetism of the solar and stellar chromospheres.

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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 (BH) 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 BH = 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. This work, presented
in an oral contribution at this Workshop, has been published on The
Astrophysical Journal (Ishikawa et al. 2017).

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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.

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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.

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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.

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Title: Rayleigh Scattering in Spectral Series with L-term Interference
Authors: Casini, R.; Manso Sainz, R.; del Pino Alemán, T.
2017ApJ...850..162C Altcode: 2017arXiv171011491C
We derive a formalism to describe the scattering of polarized radiation
over the full spectral range encompassed by atomic transitions belonging
to the same spectral series (e.g., the H I Lyman and Balmer series,
the UV multiplets of Fe I and Fe II). This allows us to study the role
of radiation-induced coherence among the upper terms of the spectral
series, and its contribution to Rayleigh scattering and the polarization
of the solar continuum. We rely on previous theoretical results for
the emissivity of a three-term atom of the Λ-type, taking into account
partially coherent scattering, and generalize its expression in order
to describe a “multiple Λ” atomic system underlying the formation
of a spectral series. Our study shows that important polarization
effects must be expected because of the combined action of partial
frequency redistribution and radiation-induced coherence among the
terms of the series. In particular, our model predicts the correct
asymptotic limit of 100% polarization in the far wings of a complete
(i.e., {{Δ }}L=0,+/- 1) group of transitions, which must be expected
on the basis of the principle of spectroscopic stability.

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Title: Explicit Form of the Radiative and Collisional Branching
Ratios in Polarized Radiation Transport with Coherent Scattering
Authors: Casini, R.; del Pino Alemán, T.; Manso Sainz, R.
2017ApJ...848...99C Altcode: 2017arXiv170900126C
We consider the vector emissivity of the polarized radiation transfer in
a Λ-type atomic transition, which we recently proposed to account for
both complete frequency redistribution (CRD) and partial redistribution
(PRD) contributions to the scattered radiation. This expression
can concisely be written as ɛ = ( ɛ ( 1 ) - ɛ f . s . ( 2 ) )
+ ɛ ( 2 ) , where {{\boldsymbol{\varepsilon }}}(1) and
{{\boldsymbol{\varepsilon }}}(2) are the emissivity terms
describing, respectively, one-photon and two-photon processes in a
Λ-type atom, and where “f.s.” means that the corresponding term
must be evaluated assuming an appropriate “flat spectrum” average
of the incident radiation across the spectral line. In this follow-up
study, we explicitly consider the expressions of these various terms
for the case of a polarized multi-term atom to derive the algebraic
forms of the branching ratios between the CRD and PRD contributions
to the emissivity. In the limit of a two-term atom with non-coherent
lower term, our results are shown to be in full agreement with those
recently derived by Bommier.

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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: A Note on the Radiative and Collisional Branching Ratios in
Polarized Radiation Transport with Coherent Scattering
Authors: Casini, R.; del Pino Alemán, T.; Manso Sainz, R.
2017ApJ...835..114C Altcode: 2016arXiv161203440C
We discuss the implementation of physically meaningful branching
ratios between the CRD and partial redistribution contributions to
the emissivity of a polarized multi-term atom in the presence of
both inelastic and elastic collisions. Our derivation is based on
a recent theoretical formulation of partially coherent scattering,
and it relies on a heuristic diagrammatic analysis of the various
radiative and collisional processes to determine the proper form of
the branching ratios. The expression we obtain for the emissivity
is {\boldsymbol{\varepsilon }}=[{{\boldsymbol{\varepsilon
}}}(1)-{{\boldsymbol{\varepsilon
}}}{{f}.{{s}}.}(2)]+{{\boldsymbol{\varepsilon
}}}(2), where {{\boldsymbol{\varepsilon }}}(1) and
{{\boldsymbol{\varepsilon }}}(2) are the emissivity terms for
the redistributed and partially coherent radiation, respectively, and
where “f.s.” implies that the corresponding term must be evaluated
assuming a flat-spectrum average of the incident radiation. This result
is shown to be in agreement with prior literature on the subject in
the limit of the unpolarized multi-level atom.

---------------------------------------------------------
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-1, 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: Laboratory Frequency Redistribution Function for the Polarized
Λ -type Three-term Atom
Authors: Casini, R.; Manso Sainz, R.
2016ApJ...833..197C Altcode: 2016arXiv161204362C
We present the frequency redistribution function for a polarized
three-term atom of the Λ-type in the collisionless regime, and we
specialize it to the case where both the initial and final terms of
the three-state transition are metastable (I.e., with infinitely sharp
levels). This redistribution function represents a generalization of
the well-known R II function to the case where the lower
terms of the transition can be polarized and carry atomic coherence,
and it can be applied to the investigation of polarized line formation
in tenuous plasmas, where collisional rates may be low enough that
anisotropy-induced atomic polarization survives even in the case of
metastable levels.

---------------------------------------------------------
Title: Magnetic Diagnostics of the Solar Chromosphere with the Mg
II h-k Lines
Authors: del Pino Alemán, T.; Casini, R.; Manso Sainz, R.
2016ApJ...830L..24D Altcode: 2016arXiv160705683D
We investigated the formation of the Mg II h-k doublet in a weakly
magnetized atmosphere (20-100 G) using a newly developed numerical
code for polarized radiative transfer in a plane-parallel geometry,
which implements a recent formulation of partially coherent scattering
by polarized multi-term atoms in arbitrary magnetic-field regimes. Our
results confirm the importance of partial redistribution effects in
the formation of the Mg II h and k lines, as pointed out by previous
work in the non-magnetic case. We show that the presence of a magnetic
field can produce measurable modifications of the broadband linear
polarization even for relatively small field strengths (∼10 G), while
the circular polarization remains well represented by the classical
magnetograph formula. Both these results open an important new window
for the weak-field diagnostics of the upper solar atmosphere.

---------------------------------------------------------
Title: Frequency Redistribution of Polarized Light in the Λ-Type
Multi-Term Polarized Atom
Authors: Casini, R.; Manso Sainz, R.
2016ApJ...824..135C Altcode: 2016arXiv160207173C
We study the effects of Rayleigh and Raman scattering on the formation
of polarized spectral lines in a Λ-type multi-term atom. We fully
take into account the partial redistribution of frequency and the
presence of atomic polarization in the lower states of the atomic
model. Problems that can be modeled with this formalism include, for
example, the formation of the Ca II H-K and IR triplet, the analogous
system of Ba II, and the Lyβ-Hα system of hydrogenic ions.

---------------------------------------------------------
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: 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: Estimating the magnetic field strength from magnetograms
Authors: Asensio Ramos, A.; Martínez González, M. J.; Manso Sainz, R.
2015A&A...577A.125A Altcode: 2015arXiv150307670A
A properly calibrated longitudinal magnetograph is an instrument
that measures circular polarization and gives an estimation of the
magnetic flux density in each observed resolution element. This usually
constitutes a lower bound of the field strength in the resolution
element, given that it can be made arbitrarily large as long as it
occupies a proportionally smaller area of the resolution element
and/or becomes more transversal to the observer while still produce
the same magnetic signal. However, we know that arbitrarily stronger
fields are less likely - hG fields are more probable than kG fields,
with fields above several kG virtually absent - and we may even have
partial information about their angular distribution. Based on a set of
sensible considerations, we derive simple formulae based on a Bayesian
analysis to give an improved estimation of the magnetic field strength
for magnetographs.

---------------------------------------------------------
Title: Spectro-Polarimetric Imaging Reveals Helical Magnetic Fields
in Solar Prominence Feet
Authors: Martínez González, M. J.; Manso Sainz, R.; Asensio Ramos,
A.; Beck, C.; de la Cruz Rodríguez, J.; Díaz, A. J.
2015ApJ...802....3M Altcode: 2015arXiv150103295M
Solar prominences are clouds of cool plasma levitating above
the solar surface and insulated from the million-degree corona by
magnetic fields. They form in regions of complex magnetic topology,
characterized by non-potential fields, which can evolve abruptly,
disintegrating the prominence and ejecting magnetized material
into the heliosphere. However, their physics is not yet fully
understood because mapping such complex magnetic configurations
and their evolution is extremely challenging, and must often be
guessed by proxy from photometric observations. Using state-of-the-art
spectro-polarimetric data, we reconstruct the structure of the magnetic
field in a prominence. We find that prominence feet harbor helical
magnetic fields connecting the prominence to the solar surface below.

---------------------------------------------------------
Title: Constraining the shaping mechanism of the Red Rectangle
through the spectro-polarimetry of its central star
Authors: Martínez González, M. J.; Asensio Ramos, A.; Manso Sainz,
R.; Corradi, R. L. M.; Leone, F.
2015A&A...574A..16M Altcode: 2014arXiv1410.6365M
We carried out high-sensitivity spectro-polarimetric observations of
the central star of the Red Rectangle protoplanetary nebula with the
aim of constraining the mechanism that gives its biconical shape. The
stellar light of the central binary system is linearly polarised since
it is scattered on the dust particles of the nebula. Surprisingly,
the linear polarisation in the continuum is aligned with one of the
spikes of the biconical outflow. Also, the observed Balmer lines,
as well as the Ca ii K lines, are polarised. These observational
constraints are used to confirm or reject current theoretical models
for the shaping mechanism of the Red Rectangle. We propose that the
observed polarisation is not very likely to be generated by a uniform
biconical stellar wind. Also, the hypothesis of a precessing jet does
not completely match observations since it requires a larger aperture
jet than for the nebula.

---------------------------------------------------------
Title: Magnetic and Dynamical Photospheric Disturbances Observed
During an M3.2 Solar Flare
Authors: Kuckein, C.; Collados, M.; Manso Sainz, R.
2015ApJ...799L..25K Altcode: 2015arXiv150104207K
This Letter reports on a set of full-Stokes spectropolarimetric
observations in the near-infrared He i 10830 Å spectral region
covering the pre-flare, flare, and post-flare phases of an M3.2 class
solar flare. The flare originated on 2013 May 17 and belonged to
active region NOAA 11748. We detected strong He i 10830 Å emission
in the flare. The red component of the He i triplet peaks at an
intensity ratio to the continuum of about 1.86. During the flare,
He i Stokes V is substantially larger and appears reversed compared
to the usually larger Si i Stokes V profile. The photospheric Si i
inversions of the four Stokes profiles reveal the following: (1) the
magnetic field strength in the photosphere decreases or is even absent
during the flare phase, as compared to the pre-flare phase. However,
this decrease is not permanent. After the flare, the magnetic field
recovers its pre-flare configuration in a short time (i.e., 30 minutes
after the flare). (2) In the photosphere, the line of sight velocities
show a regular granular up- and downflow pattern before the flare
erupts. During the flare, upflows (blueshifts) dominate the area where
the flare is produced. Evaporation rates of ∼ {{10}-3}
and ∼ {{10}-4} g cm-2 s-1 have been
derived in the deep and high photosphere, respectively, capable of
increasing the chromospheric density by a factor of two in about 400 s.

---------------------------------------------------------
Title: Abundance Determinations in Ionized Nebulae and their
Sensitivity to Temperature
Authors: Rodríguez, M.; Manso Sainz, R.
2014RMxAC..44...22R Altcode:
Our main source of uncertainty in the determination of chemical
abundances in H II regions and planetary nebulae arises from a
discrepancy: the abundances implied by recombination lines are larger
than those implied by collisionally excited lines. The discrepancy
amounts to a factor of 2 in most objects, but reaches much higher values
in some planetary nebulae. There are several possible explanations for
this effect. Here we explore a recent proposal and determine what kind
of deviations from a Maxwellian electron energy distribution are needed
in order to reproduce the measured abundance discrepancies. We note
the parallelisms between this explanation and other explanations that
are based on the sensitivity to temperature of collisionally excited
lines: the presence of metal-rich inclusions within the ionized gas
or temperature fluctuations in a chemically homogeneous gas.

---------------------------------------------------------
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: Frequency Redistribution Function for the Polarized Two-term
Atom
Authors: Casini, R.; Landi Degl'Innocenti, M.; Manso Sainz, R.;
Landi Degl'Innocenti, E.; Landolfi, M.
2014ApJ...791...94C Altcode: 2014arXiv1406.6129C
We present a generalized frequency redistribution function for the
polarized two-term atom in an arbitrary magnetic field. This result is
derived within a new formulation of the quantum problem of coherent
scattering of polarized radiation by atoms in the collisionless
regime. The general theory, which is based on a diagrammatic treatment
of the atom-photon interaction, is still a work in progress. However,
the results anticipated here are relevant enough for the study of the
magnetism of the solar chromosphere and of interest for astrophysics in
general. The National Center for Atmospheric Research is sponsored
by the National Science Foundation.

---------------------------------------------------------
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 &lt;= 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: Upper Limits to the Magnetic Field in Central Stars of
Planetary Nebulae
Authors: Asensio Ramos, A.; Martínez González, M. J.; Manso Sainz,
R.; Corradi, R. L. M.; Leone, F.
2014ApJ...787..111A Altcode: 2014arXiv1404.2718A
More than about 20 central stars of planetary nebulae (CSPNs) have
been observed spectropolarimetrically, yet no clear, unambiguous
signal of the presence of a magnetic field in these objects has
been found. We perform a statistical (Bayesian) analysis of all the
available spectropolarimetric observations of CSPN to constrain the
magnetic fields in these objects. Assuming that the stellar field is
dipolar and that the dipole axis of the objects is oriented randomly
(isotropically), we find that the dipole magnetic field strength
is smaller than 400 G with 95% probability using all available
observations. The analysis introduced allows integration of future
observations to further constrain the parameters of the distribution,
and it is general, so that it can be easily applied to other classes of
magnetic objects. We propose several ways to improve the upper limits
found here.

---------------------------------------------------------
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: A search for magnetic fields on central stars in planetary
nebulae
Authors: Leone, F.; Corradi, R. L. M.; Martínez González, M. J.;
Asensio Ramos, A.; Manso Sainz, R.
2014A&A...563A..43L Altcode: 2014arXiv1401.6282L
Context. One of the possible mechanisms responsible for the panoply
of shapes in planetary nebulae is the presence of magnetic fields
that drive the ejection of ionized material during the proto-planetary
nebula phase. Aims: Therefore, detecting magnetic fields in such
objects is of key importance for understanding their dynamics. Still,
magnetic fields have not been detected using polarimetry in the central
stars of planetary nebulae. Methods: Circularly polarized light
spectra have been obtained with the Focal Reducer and Low Dispersion
Spectrograph at the Very Large Telescope of the European Southern
Observatory and the Intermediate dispersion Spectrograph and Imaging
System at the William Herschel Telescope. Twentythree planetary nebulae
that span very different morphology and evolutionary stages have been
selected. Most of central stars have been observed at different rotation
phases to point out evidence of magnetic variability. Results:
In this paper, we present the result of two observational campaigns
aimed to detect and measure the magnetic field in the central stars of
planetary nebulae on the basis of low resolution spectropolarimetry. In
the limit of the adopted method, we can state that large scale fields
of kG order are not hosted on the central star of planetary nebulae.

---------------------------------------------------------
Title: Magnetic, Thermal and Dynamical Evolution of AN M3.2 Two-Ribbon
Flare
Authors: Collados, Manuel; Kuckein, Christoph; Manso Sainz, Rafael;
Asensio Ramos, Andres
2014cosp...40E.568C Altcode:
On 2013, 17th May, a two-ribbon M3.2 flare took place in the solar
atmosphere on the active region AR 11748. The flare evolution was
observed at the German VTT of the Observatorio del Teide using the
instrument TIP-II, with spectropolarimetric measurements of the
photosphere (Si I at 1082.7 nm) and the chromosphere (Helium triplet
at 1083 nm). Simultaneous spectroscopic data of the chromospheric
spectral line of Ca II at 854.2 nm and filtergrams at Halpha were
also obtained. The flare evolution as observed from the ground can be
compared with the changes observed by AIA@SDO at different ultraviolet
wavelengths. The ground observations covered several hours, including
the pre-flare, impulsive, gradual and post-flare phases. We present
maps of the magnetic field, thermal and dynamical properties of the
region during its evolution from pre- to post-flare phase.

---------------------------------------------------------
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: Signal detection for spectroscopy and polarimetry
Authors: Asensio Ramos, A.; Manso Sainz, R.
2013hsa7.conf..771A Altcode:
Spectroscopic and spectropolarimetric observations with high
spectral resolution provide extremely rich information on the
physical conditions of distant celestial objects; sometimes, even the
mere presence of a spectroscopic or polarimetric pattern may offer
fundamental insights. But these are photon-starving techniques. Signals
are often at the noise level or buried in it and, many times, just
detection proves difficult. Here we present a Bayesian technique for
the detection of spectropolarimetric signals based on the application
of the non-parametric relevance vector machine to the observations,
which allows computing the evidence for the presence of a signal and
its most probable value.

---------------------------------------------------------
Title: Hanle Effect for Stellar Dipoles and Quadrupoles
Authors: Manso Sainz, R.; Martínez González, M. J.
2012ApJ...760....7M Altcode: 2012arXiv1209.6187M
We derive exact expressions for the degree of lineal polarization over
a resolved or integrated stellar disc due to resonance scattering
and the Hanle effect from a dipolar or quadrupolar distribution of
magnetic fields. We apply the theory of scattering polarization within
the formalism of the spherical tensors representation for the density
matrix and radiation field. The distribution of linear polarization
over the stellar disk for different configurations of the magnetic
field is studied and its topology discussed. For an unresolved dipole,
the resulting polarization can be expressed in terms of just three
functions (of the inclination angle and effective dipole strength)
that are calculated numerically and their behavior discussed. Dipolar
and (aligned) quadrupoles are considered in some detail, but the
techniques here—in particular, the extensive use of the spherical
tensor formalism for polarization—can easily be applied to more
general field configurations.

---------------------------------------------------------
Title: Anomalous Circular Polarization Profiles in the He I 1083.0
nm Multiplet from Solar Spicules
Authors: Martínez González, M. J.; Asensio Ramos, A.; Manso Sainz,
R.; Beck, C.; Belluzzi, L.
2012ApJ...759...16M Altcode: 2012arXiv1209.2589M
We report Stokes vector observations of solar spicules and a prominence
in the He I 1083 nm multiplet carried out with the Tenerife Infrared
Polarimeter. The observations show linear polarization profiles that
are produced by scattering processes in the presence of a magnetic
field. After a careful data reduction, we demonstrate the existence of
extremely asymmetric Stokes V profiles in the spicular material that
we are able to model with two magnetic components along the line of
sight, and under the presence of atomic orientation in the energy
levels that give rise to the multiplet. We discuss some possible
scenarios that can generate the atomic orientation in spicules. We
stress the importance of spectropolarimetric observations across the
limb to distinguish such signals from observational artifacts.

---------------------------------------------------------
Title: Signal detection for spectroscopy and polarimetry
Authors: Asensio Ramos, A.; Manso Sainz, R.
2012A&A...547A.113A Altcode: 2012arXiv1209.6455A
The analysis of high spectral resolution spectroscopic and
spectropolarimetric observations constitutes a very powerful way of
inferring the dynamical, thermodynamical, and magnetic properties of
distant objects. However, these techniques starve photons, making
it difficult to use them for all purposes. A common problem is not
being able to detect a signal because it is buried on the noise at
the wavelength of some interesting spectral feature. This problem is
especially relevant for spectropolarimetric observations, because only a
small fraction of the received light is typically polarized. We present
in this paper a Bayesian technique for detecting spectropolarimetric
signals. The technique is based on applying the nonparametric relevance
vector machine to the observations, which allows us to compute the
evidence for the presence of the signal and compute the more probable
signal. The method is suited for analyzing data from experimental
instruments onboard space missions and rockets aiming at detecting
spectropolarimetric signals in unexplored regions of the spectrum,
such as the Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP)
sounding rocket experiment.

---------------------------------------------------------
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: Resonance scattering polarization in the magnetosphere
of Mercury
Authors: López Ariste, A.; Leblanc, F.; Casini, R.; Manso Sainz,
R.; Gelly, B.; Le Men, C.
2012Icar..220.1104L Altcode:
The conditions of the exosphere of Mercury constitute a prime example
of a magnetosphere subject to space weather. We aim at improving the
diagnostic of the physical conditions of Na atoms in the exosphere of
Mercury, with particular emphasis in the possibility of inferring the
magnetic field through polarimetry of the Na D emission lines. We
performed spectropolarimetry of the Na D emission lines in the
exosphere of Mercury at two different ranges of phases of the planet
and interpreted them under present models of resonance scattering
polarization applied to the Na atom. We measured successfully the
polarization of the Na D2 line while no polarization
was seen in D1, as expected. The measured polarization
varies with the phase angle but it is roughly a factor two smaller
than expected from an isolated emitting atom. Depolarization due to
the presence of optical depth explains this factor two and is the
most probable explanation for this discrepancy. A framework for the
observation of polarization in the emission lines of the exosphere and
its interpretation is laid. This opens the possibility to use these
measurements for diagnostic of the physical conditions in the exosphere
of Mercury, and eventually to infer the magnetic field of Mercury and
its variability from observations made with ground telescopes.

---------------------------------------------------------
Title: Dead Calm Areas in the Very Quiet Sun
Authors: Martínez González, M. J.; Manso Sainz, R.; Asensio Ramos,
A.; Hijano, E.
2012ApJ...755..175M Altcode: 2012arXiv1206.4545M
We analyze two regions of the quiet Sun (35.6 × 35.6 Mm2)
observed at high spatial resolution (lsim100 km) in polarized light by
the IMaX spectropolarimeter on board the SUNRISE balloon. We identify
497 small-scale (~400 km) magnetic loops, appearing at an effective
rate of 0.25 loop h -1 arcsec-2 further, we
argue that this number and rate are underestimated by ~30%. However,
we find that these small dipoles do not appear uniformly on the solar
surface: their spatial distribution is rather filamentary and clumpy,
creating dead calm areas, characterized by a very low magnetic signal
and a lack of organized loop-like structures at the detection level
of our instruments, which cannot be explained as just statistical
fluctuations of a Poisson spatial process. We argue that this is an
intrinsic characteristic of the mechanism that generates the magnetic
fields in the very quiet Sun. The spatio-temporal coherences and the
clumpy structure of the phenomenon suggest a recurrent, intermittent
mechanism for the generation of magnetic fields in the quietest areas
of the Sun.

---------------------------------------------------------
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. 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: Model Selection for Spectropolarimetric Inversions
Authors: Asensio Ramos, A.; Manso Sainz, R.; Martínez González,
M. J.; Viticchié, B.; Orozco Suárez, D.; Socas-Navarro, H.
2012ApJ...748...83A Altcode: 2012arXiv1201.5063A
Inferring magnetic and thermodynamic information from
spectropolarimetric observations relies on the assumption of
a parameterized model atmosphere whose parameters are tuned by
comparison with observations. Often, the choice of the underlying
atmospheric model is based on subjective reasons. In other cases,
complex models are chosen based on objective reasons (for instance,
the necessity to explain asymmetries in the Stokes profiles) but it
is not clear what degree of complexity is needed. The lack of an
objective way of comparing models has, sometimes, led to opposing
views of the solar magnetism because the inferred physical scenarios
are essentially different. We present the first quantitative model
comparison based on the computation of the Bayesian evidence ratios for
spectropolarimetric observations. Our results show that there is not
a single model appropriate for all profiles simultaneously. Data with
moderate signal-to-noise ratios (S/Ns) favor models without gradients
along the line of sight. If the observations show clear circular and
linear polarization signals above the noise level, models with gradients
along the line are preferred. As a general rule, observations with large
S/Ns favor more complex models. We demonstrate that the evidence ratios
correlate well with simple proxies. Therefore, we propose to calculate
these proxies when carrying out standard least-squares inversions to
allow for model comparison in the future.

---------------------------------------------------------
Title: Analytical maximum likelihood estimation of stellar magnetic
fields
Authors: Martínez González, M. J.; Manso Sainz, R.; Asensio Ramos,
A.; Belluzzi, L.
2012MNRAS.419..153M Altcode: 2011MNRAS.tmp.1583M; 2011arXiv1108.4366M
The polarized spectrum of stellar radiation encodes valuable information
on the conditions of stellar atmospheres and the magnetic fields
that permeate them. In this paper, we give explicit expressions to
estimate the magnetic field vector and its associated error from the
observed Stokes parameters. We study the solar case where specific
intensities are observed and then the stellar case, where we receive
the polarized flux. In the second case, we concentrate on the explicit
expression for the case of a slow rotator with a dipolar magnetic
field geometry. Moreover, we also give explicit formulae to retrieve
the magnetic field vector from the least-squares deconvolution (LSD)
profiles without assuming mean values for the LSD artificial spectral
line. The formulae have been obtained assuming that the spectral lines
can be described in the weak-field regime and using a maximum likelihood
approach. The errors are recovered by means of the Hermitian matrix. The
bias of the estimators is analysed in depth.

---------------------------------------------------------
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: 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: Polarization Diagnostics of Solar Magnetic Fields
Authors: Manso Sainz, R.
2011AGUFM.P14C..01M Altcode:
The solar atmosphere is a highly ionized medium which is the playground
of magnetic fields. In the deepest layer (the photosphere), magnetic
fields disturb the 'normal' fluid motions forcing the plasma to behave
incounterintuitive ways; in the outer layers (the chromosphere and
the corona) magnetic fields rule, making the plasma levitate or even
ejecting it out of the gravitational well of the Sun, with important
consequences for us here on Earth. However, magnetic fields are
elusive. The only quantitative evidence of their presence is through
the polarization state of the light emitted by the plasma they are
playing with. Remote sensing of magnetic fields from 150 million km away
through spectropolarimetry is a challenge on applied physics as well
as an art. It requires the application of quantum mechanics, radiative
transfer theory, and advanced optics to the interpretation and analysis
of spectropolarimetric observations. I will review standard diagnostic
techniques and recent developments on this field. I will discuss their
limitations and how to overcome them through the complementary aspects
of different diagnostic techniques, spectral regions, and statistical
analysis. Finally, I will review what are the main areas for progress
in this regard: most notably, the 'measurement' of magnetic fields in
the extremely dilute and weakly magnetized outer layers of the sun.

---------------------------------------------------------
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: 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: Advection and dispersal of small magnetic elements in the
very quiet Sun
Authors: Manso Sainz, R.; Martínez González, M. J.; Asensio Ramos, A.
2011A&A...531L...9M Altcode:
We track small magnetic structures on very quiet regions (internetwork)
of the Sun. We follow the footpoints of small-scale magnetic loops that
appear on the photosphere at granular scales using spectropolarimetric
and magnetographic data obtained with Hinode. We find two different
regimes for their wanderings. Within granules (where they appear),
they seem to be passively advected by the plasma - which is
justified by their relatively low magnetic flux (~1016
Mx), and magnetic field strength (~200 G). The plasma flow thus
traced is roughly laminar with a characteristic mean velocity of 2
km s-1 and very low vorticity. Once the magnetic markers
reach intergranular lanes, they remain there and are buffeted by the
random flows of neighbouring granules and turbulent intergranules,
follow random walks, and disperse across the solar surface with a
diffusion constant of 195 km2 s-1. While on
their intergranular random walking, they may fall close to whirlpools
(on scales ≲400 km) associated with convective downdrafts, similar
to the events recently reported in mesogranular and supergranular cell
boundaries tracking magnetic bright points, which provides additional
evidence that these events are ubiquitous on the solar surface.

---------------------------------------------------------
Title: A Sounding Rocket Experiment for Spectropolarimetric
Observations with the Lyα 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 Lyα 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 Lyα 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: Non-detection of Magnetic Fields in the Central Stars of the
Planetary Nebulae NGC 1360 and LSS 1362
Authors: Leone, Francesco; Martínez González, María J.; Corradi,
Romano L. M.; Privitera, Giovanni; Manso Sainz, Rafael
2011ApJ...731L..33L Altcode: 2011arXiv1104.1042L
The presence of magnetic fields is an attractive hypothesis for shaping
planetary nebulae (PNe). We report on observations of the central star
of the two PNe NGC 1360 and LSS 1326. We performed spectroscopy on
circularly polarized light with the Focal Reducer and Low Dispersion
Spectrograph at the Very Large Telescope of the European Southern
Observatory. Contrary to previous reports, we find that the effective
magnetic field, which is the average over the visible stellar disk of
longitudinal components of the magnetic fields, is null within errors
for both stars. We conclude that direct evidence of magnetic fields on
the central stars of PNe is still missing—either the magnetic field
is much weaker (&lt;600 G) than previously reported, or more complex
(thus leading to cancellations), or both. Certainly, indirect evidence
(e.g., MASER emission) fully justify further efforts to point out the
strength and morphology of such magnetic fields.

---------------------------------------------------------
Title: On the Inversion of Stokes Profiles with Local Stray-light
Contamination
Authors: Asensio Ramos, A.; Manso Sainz, R.
2011ApJ...731..125A Altcode: 2011arXiv1102.4703A
Obtaining the magnetic properties of non-resolved structures in the
solar photosphere is always challenging and problems arise because
the inversion is carried out through the numerical minimization of a
merit function that depends on the proposed model. We investigate the
reliability of inversions in which the stray-light contamination is
obtained from the same observations as a local average. In this case,
we show that it is fundamental to include the covariance between
the observed Stokes profiles and the stray-light contamination. The
ensuing modified merit function of the inversion process penalizes
large stray-light contaminations simply because of the presence of
positive correlations between the observables and the stray light,
fundamentally produced by spatially variable systematics. We caution
that if the wrong merit function is used, artificially large stray-light
contaminations might be inferred. Since this effect disappears if the
stray-light contamination is obtained as an average over the full field
of view, we recommend taking into account stray-light contamination
using a global approach.

---------------------------------------------------------
Title: Elementary Theory of Scattering Polarization in Complex Atoms
Authors: Manso Sainz, R.
2011ASPC..437...19M Altcode:
Scattering polarization in complex atoms poses interesting theoretical
problems and is interesting for diagnostic plasma purposes. Here,
an elementary theory on the generation and transfer of scattering
polarization and Hanle effect in complex atoms (chiefly, transition
metals and rare earths) is introduced. It is based on the quantum
mechanical formulation of polarization transfer. The exposition
is self-contained and can be (and has been) applied to treat very
general problems. Numerical methods of solution are reviewed. I
discuss non-trivial problems arising not from the formalism itself,
but from its application to systems (complex atoms) with intrinsic
spectroscopic peculiarities. In particular, they have a large number
of relevant atomic levels massively interconnected between them by a
huge amount of (resonant or quasi-resonant) spectral lines. This gives
rise to surprising effects such as depolarization by interlocking,
level over-polarization, and special Hanle effect regimes.

---------------------------------------------------------
Title: Unnoticed Magnetic Field Oscillations in the Very Quiet Sun
Revealed by SUNRISE/IMaX
Authors: Martínez González, M. J.; Asensio Ramos, A.; Manso Sainz,
R.; Khomenko, E.; Martínez Pillet, V.; Solanki, S. K.; López Ariste,
A.; Schmidt, W.; Barthol, P.; Gandorfer, A.
2011ApJ...730L..37M Altcode: 2011arXiv1103.0145M
We present observational evidence for oscillations of magnetic flux
density in the quiet areas of the Sun. The majority of magnetic
fields on the solar surface have strengths of the order of or lower
than the equipartition field (300-500 G). This results in a myriad of
magnetic fields whose evolution is largely determined by the turbulent
plasma motions. When granules evolve they squash the magnetic field
lines together or pull them apart. Here, we report on the periodic
deformation of the shapes of features in circular polarization observed
at high resolution with SUNRISE. In particular, we note that the
area of patches with a constant magnetic flux oscillates with time,
which implies that the apparent magnetic field intensity oscillates
in antiphase. The periods associated with this oscillatory pattern
are compatible with the granular lifetime and change abruptly, which
suggests that these oscillations might not correspond to characteristic
oscillatory modes of magnetic structures, but to the forcing by granular
motions. In one particular case, we find three patches around the same
granule oscillating in phase, which means that the spatial coherence
of these oscillations can reach 1600 km. Interestingly, the same kind
of oscillatory phenomenon is also found in the upper photosphere.

---------------------------------------------------------
Title: Are magnetic fields shaping PNe?
Authors: Matínez González, M. J.; Leone, F.; Corradi, R.; Manso
Sainz, R.; Privitera, G.
2011iac..talk..255M Altcode: 2011iac..talk..206M
No abstract at ADS

---------------------------------------------------------
Title: Detecting photons with orbital angular momentum in extended
astronomical objects: application to solar observations
Authors: Uribe-Patarroyo, N.; Alvarez-Herrero, A.; López Ariste, A.;
Asensio Ramos, A.; Belenguer, T.; Manso Sainz, R.; Lemen, C.; Gelly, B.
2011A&A...526A..56U Altcode:
Context. The orbital angular momentum (OAM) of the photon is a
property of light from astronomical objects that has not yet been
measured. We propose a method of measuring the OAM spectrum of light
from an extended natural source, the Sun. Relating the OAM spectrum of
different solar areas to its structures could lead to a novel remote
sensing technique. Aims: We present a method for measuring the
OAM spectrum of solar photons. Methods: The THEMIS (Télescope
Héliographique pour l'Étude du Magnetisme et les Instabilités
Solaires is a 0.9 m solar telescope property of the French CNRS-INSU
at the Spanish Observatorio del Teide.) telescope is being used with
a novel phase-diversity technique. A spatial light modulator is placed
on one pupil image, and an ad-hoc optical setup allows the measurement
of two simultaneous phase-diverse images in the same CCD, with equal
optical paths. Results: Preliminary results show that very good
seeing is mandatory for this kind of observation. The method works in
the laboratory, and good seeing conditions in the 2010 campaign are
being awaited.

---------------------------------------------------------
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 &lt;~ 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: Small Magnetic Loops Connecting the Quiet Surface and the
Hot Outer Atmosphere of the Sun
Authors: Martínez González, M. J.; Manso Sainz, R.; Asensio Ramos,
A.; Bellot Rubio, L. R.
2010ApJ...714L..94M Altcode: 2010arXiv1003.1255M
Sunspots are the most spectacular manifestation of solar magnetism,
yet 99% of the solar surface remains "quiet" at any time of the solar
cycle. The quiet sun is not void of magnetic fields, though; they
are organized at smaller spatial scales and evolve relatively fast,
which makes them difficult to detect. Thus, although extensive quiet
Sun magnetism would be a natural driver to a uniform, steady heating of
the outer solar atmosphere, it is not clear what the physical processes
involved would be, due to lack of observational evidence. We report on
the topology and dynamics of the magnetic field in very quiet regions of
the Sun from spectropolarimetric observations of the Hinode satellite,
showing a continuous injection of magnetic flux with a well-organized
topology of Ω-loop from below the solar surface into the upper
layers. At first stages, when the loop travels across the photosphere,
it has a flattened (staple-like) geometry and a mean velocity ascent
of ~3 km s-1. When the loop crosses the minimum temperature
region, the magnetic fields at the footpoints become almost vertical and
the loop topology resembles a potential field. The mean ascent velocity
at chromospheric height is ~12 km s-1. The energy input rate
of these small-scale loops in the lower boundary of the chromosphere
is (at least) of 1.4 × 106-2.2 × 107 erg
cm-2 s-1. Our findings provide empirical evidence
for solar magnetism as a multi-scale system, in which small-scale
low-flux magnetism plays a crucial role, at least as important as active
regions, coupling different layers of the solar atmosphere and being
an important ingredient for chromospheric and coronal heating models.

---------------------------------------------------------
Title: Scattering Polarization in the Fe I 630 nm Emission Lines at
the Extreme Limb of the Sun
Authors: Lites, B. W.; Casini, R.; Manso Sainz, R.; Jurčák, J.;
Ichimoto, K.; Ishikawa, R.; Okamoto, T. J.; Tsuneta, S.; Bellot
Rubio, L.
2010ApJ...713..450L Altcode:
Spectro-polarimetric observations with the Solar Optical Telescope
onboard Hinode reveal the emission spectrum of the Fe I 630 nm lines
at the solar limb. The emission shell extends for less than 1” thereby
making it extremely difficult to detect from ground-based observatories
viewing the limb through the Earth's atmosphere. The linear polarization
signal is clearly due to scattering and it is predominantly oriented
in the radial direction. Using a comprehensive atomic model of
iron, we are able to interpret qualitatively the observed signals,
including the radial orientation of the linear polarization. The Hanle
effect causes the linear polarization of the Fe I 630 nm lines to be
sensitive to magnetic fields between ~0.1 G and ~40 G, and also to
be sensitive to the field's topology for stronger fields. The overall
degree of observed polarization can be reproduced by randomly oriented
horizontal magnetic fields of strength ≈2 G. The discovery of their
scattering polarization signals thus opens a new diagnostic opportunity
for these lines.

---------------------------------------------------------
Title: The stochastic, intermittent nature of quiet Sun magnetism
Authors: Martinez González, M. J.; Manso Sainz, R.; López Ariste,
A.; Bellot Rubio, L. R.; Bianda, M.
2010iac..talk....1M Altcode: 2010iac..talk..153M
No abstract at ADS

---------------------------------------------------------
Title: Statistical Analysis of the very Quiet Sun Magnetism
Authors: Martínez González, M. J.; Manso Sainz, R.; Asensio Ramos,
A.; López Ariste, A.; Bianda, M.
2010ApJ...711L..57M Altcode: 2010arXiv1001.4551M
The behavior of the observed polarization amplitudes with spatial
resolution is a strong constraint on the nature and organization
of solar magnetic fields below the resolution limit. We study the
polarization of the very quiet Sun at different spatial resolutions
using ground- and space-based observations. It is shown that 80% of the
observed polarization signals do not change with spatial resolution,
suggesting that, observationally, the very quiet Sun magnetism
remains the same despite the high spatial resolution of space-based
observations. Our analysis also reveals a cascade of spatial scales
for the magnetic field within the resolution element. It is manifest
that the Zeeman effect is sensitive to the microturbulent field usually
associated with Hanle diagnostics. This demonstrates that Zeeman and
Hanle studies show complementary perspectives of the same magnetism.

---------------------------------------------------------
Title: Polarimetric Diagnostics of Unresolved Chromospheric Magnetic
Fields
Authors: Casini, R.; Manso Sainz, R.; Low, B. C.
2009ApJ...701L..43C Altcode: 2008arXiv0811.0512C
For about a decade, spectropolarimetry of He I λ10830 has been applied
to the magnetic diagnostics of the solar chromosphere. This resonance
line is very versatile as it is visible both on disk and in off-limb
structures, and it has a good sensitivity to both the weak-field
Hanle effect and the strong-field Zeeman effect. Recent observations
of an active-region filament showed that the linear polarization was
dominated by the transverse Zeeman effect, with very little or no
hint of scattering polarization. This is surprising, since the He I
levels should be significantly polarized in a conventional scattering
scenario. To explain the observed level of atomic depolarization by
collisional or radiative processes, one must invoke plasma densities
larger by several orders of magnitude than currently known values
for prominences. We show that such depolarization can be explained
quite naturally by the presence of an unresolved, highly entangled
magnetic field, which averages to give the ordered field inferred
from spectropolarimetric data, over the typical temporal and spatial
scales of the observations. We present a modeling of the polarized He I
λ10830 in this scenario, and discuss its implications for the magnetic
diagnostics of prominences and spicules, and for the general study of
unresolved magnetic field distributions in the solar atmosphere.

---------------------------------------------------------
Title: Variability of the polarization profiles of the Ba II D{2}
line in the solar atmosphere
Authors: López Ariste, A.; Asensio Ramos, A.; Manso Sainz, R.;
Derouich, M.; Gelly, B.
2009A&A...501..729L Altcode:
Resonance-scattering polarization and the Hanle effect are powerful
but seldom exploited probes into the magnetism of the quiet solar
atmosphere. They are also very interesting checks of the quantum theory
of atomic polarization. The Ba ii D2 line has been known for more than
20 years as presenting a conspicuous signal of resonance scattering
polarization thanks to its atomic configuration and the presence
of five different isotopes of Ba, two of which present a hyperfine
structure.A model that considers most of the known ingredients of the
atomic polarization of Ba ii related to the formation of the D2 line
was presented in 2007. We intend to observe all the variability of the
Stokes profiles of this line in conditions of resonance scattering
to verify the general validity of the model and to ascertain the
use of the model for magnetic field diagnostics in the quiet solar
chromosphere and in spicules. The new CCD cameras at THEMIS and the
recently commissioned tip-tilt tracking system gave us the opportunity
to perform the required observations with unprecedented precision
and reliability, resulting in data ready to confront the present
theory.The Stokes Q profiles, both off-limb and on disk, appear to
verify this theory in qualitative terms. The observed departures in
terms of overall signal amplitude and relative ratios among the three
spectral features point to a refinement of the theory for quantitative
purposes, perhaps including radiative-transfer effects. We observed,
on the other hand, anomalous Stokes V profiles in the absence of Zeeman
effect that remain unexplained.The qualitative agreement between the
theory and the observations encourages an increased effort to also
match the observations from a quantitative point of view, including
the observed anomalous Stokes V profiles.

---------------------------------------------------------
Title: Magnetic field strength of active region filaments
Authors: Kuckein, C.; Centeno, R.; Martínez Pillet, V.; Casini, R.;
Manso Sainz, R.; Shimizu, T.
2009A&A...501.1113K Altcode: 2009arXiv0904.4876K
Aims: We study the vector magnetic field of a filament observed over a
compact active region neutral line. Methods: Spectropolarimetric
data acquired with TIP-II (VTT, Tenerife, Spain) of the 10 830
Å spectral region provide full Stokes vectors that were analyzed
using three different methods: magnetograph analysis, Milne-Eddington
inversions, and PCA-based atomic polarization inversions. Results:
The inferred magnetic field strengths in the filament are around 600-700
G by all these three methods. Longitudinal fields are found in the
range of 100-200 G whereas the transverse components become dominant,
with fields as high as 500-600 G. We find strong transverse fields
near the neutral line also at photospheric levels. Conclusions:
Our analysis indicates that strong (higher than 500 G, but below kG)
transverse magnetic fields are present in active region filaments. This
corresponds to the highest field strengths reliably measured in these
structures. The profiles of the helium 10 830 Å lines observed in
this active region filament are dominated by the Zeeman effect.

---------------------------------------------------------
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 (Ne) and to the magnetic field
orientation although not to the field strength. At Ne∼
10^7~cm-3 the linear polarization would be ∼1% just
over the solar surface and ∼5% at 0.2R_⊙, rapidly decaying for
Ne&gt; 10^8~cm-3. The mechanism works for other
spectral lines and ions too.

---------------------------------------------------------
Title: Near-IR internetwork spectro-polarimetry at different
heliocentric angles
Authors: Martínez González, M. J.; Asensio Ramos, A.; López Ariste,
A.; Manso Sainz, R.
2008A&A...479..229M Altcode: 2007arXiv0710.5219M
Aims:The analysis of near infrared spectropolarimetric data at the
internetwork in different regions on the solar surface could offer
constraints that reject current modeling of these quiet areas. Methods: We present spectro-polarimetric observations of very
quiet regions for different values of the heliocentric angle for the
Fe i lines at 1.56 μm, from disc centre to positions close to the
limb. The spatial resolution of the data is 0.7{-}1”. We analyse
direct observable properties of the Stokes profiles as the amplitude
of circular and linear polarisation, as well as the total degree of
polarisation. The area and amplitude asymmetries are also studied. Results: We do not find any significant variation in the properties of
the polarimetric signals with the heliocentric angle. This means that
the magnetism of the solar internetwork remains the same regardless
of the position on the solar disc. This observational fact discards
the possibility of modeling the internetwork as a network-like
scenario. The magnetic elements of internetwork areas seem to be
isotropically distributed when observed at our spatial resolution.

---------------------------------------------------------
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. 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. 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. 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. 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. Appendices
A and B are only available in electronic form at http://www.aanda.org

---------------------------------------------------------
Title: Turbulent fields in the quiet sun from Hanle and Zeeman
effects with THEMIS
Authors: López Ariste, A.; Malherbe, J. M.; Manso Sainz, R.; Asensio
Ramos, A.; Ramírez Vélez, J. C.; Martínez González, M.
2007sf2a.conf..596L Altcode:
The measurement of the Sr I line with full polarimetry and spatial
resolution with THEMIS has provided the unexpected result of an apparent
correlation between the Hanle effect signals and the Zeeman effect
signals on this line. Traditionnally, Hanle effect signals in linear
polarisation have been interpreted as the signature of unorganized,
turbulent fields, while Zeeman effect signals -mostly in circular
polarisation- were interpreted as structured fields. The correlation
between both observed by THEMIS requires a change of mind respect to the
picture of the quiet sun, with fewer structured fields and a turbulent
field visible also in deep magnetograms. This picture is supported also
by recent results with Mn lines with strong coupling with its hyperfine
structure and of center-to-limb histograms of Zeeman amplitudes.

---------------------------------------------------------
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
10-3 in its two strongest lines and at the 10-4
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: A synthetic stellar polarization atlas from 400 to 1000 nm
Authors: Socas-Navarro, H.; Asensio Ramos, A.; Manso Sainz, R.
2007A&A...465..339S Altcode: 2006astro.ph.12388S
Context: With the development of new polarimeters for large telescopes,
the spectro-polarimetric study of astrophysical bodies is becoming
feasible and, indeed, more frequent. In particular, this is permitting
the observational study of stellar magnetic fields. Aims: With
the aim to optimize and interpret this kind of observations, we have
produced a spectral atlas of circular polarization in a grid of stellar
atmospheric models with effective temperatures between 3500 and 10 000
K, surface gravities log(g)=3.5-5, metallicities between 10-2
and 1, and magnetic field strengths of 100, 1000 and 5000 G. Methods: We have computed the emergent Stokes I and V flux spectra
in LTE of more than 105 spectral lines. Results: The
atlas and several numerical tools are available in electronic format
and may be downloaded from http://download.hao.ucar.edu/pub/PSA/. In
this paper we review and discuss some of its most relevant features,
such as which spectral regions and individual lines harbor the
strongest signals, what are interesting lines to observe, how to
disentangle field strength from filling factor, etc. Full
line lists and spectra are only available in electronic form at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsweb.u-strasbg.fr/cgi-bin/ qcat?J/A+A/465/339

---------------------------------------------------------
Title: VizieR Online Data Catalog: Synthetic stellar polarization
400-1000nm (Socas-Navarro+ 2007)
Authors: Socas-Navarro, H.; Asensio Ramos, A.; Manso Sainz, R.
2007yCat..34650339S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Effect of Turbulent Electric Fields on the Scattering
Polarization of Hydrogen Lines
Authors: Casini, R.; Manso Sainz, R.
2006ASPC..358..429C Altcode:
We reviewed the polarization properties of hydrogen lines in the
presence of electric and magnetic fields. We first considered the
case of completely depolarized hydrogen atoms. Under this assumption,
the hydrogen lines manifest complex polarization signatures due to
the combined Stark and Zeeman effect tep{c0 CL93}. One can derive
convenient analytic expressions for the 1st and 2nd-order moments
of the Stokes profile, which nicely summarize the fundamental
properties of hydrogen polarization for both cases of deterministic
and micro-turbulent electric and magnetic fields tep{c0 CL94,c0
CL95,c0 Ca97}. In particular, it is demonstrated the “additivity”
of the Stark and Zeeman effects on such integral properties of the
line polarization emitted by a gas of depolarized hydrogen atoms. We
then generalized the problem to include the possibility of atomic
polarization induced in the hydrogen atoms by anisotropic excitation
mechanisms (e.g., in chromospheric and coronal plasmas). The complexity
of the problem makes it intractable by analytic means, and one must
resort to numerical tools. The results show that, in the presence of
atomic polarization, the “additivity” of the electric and magnetic
effects is lost, and an intricated interplay of the two effects occurs
tep{c0 Ca05}. In particular, we considered two hydrogen lines of
diagnostic relevance-Lyα and Hα-formed in a magnetized plasma, and
demonstrated the modifications of the scattering polarization that are
induced by the additional presence of turbulent, electric microfields
of various strengths (typically, the normal field strength of the
Holtsmark theory, for various electron densities of the plasma). We
showed that the additional presence of these electric microfields can
significantly enhance the amount of net circular polarization (NCP) of
the Hα line for a given magnetic strength, which can be produced by the
so-called alignment-to-orientation transfer mechanism tep[e.g.,][]{c0
La82,c0 Ke84,c0 LL04}, even if the electric microfield distribution is
perfectly isotropic tep[see Fig. ref{c0 NCP};][]{c0 CM06}. We argued
that this mechanism could explain the large levels of NCP that have
recently been detected in several quiescent prominences tep{c0 LA05},
and discussed the implications of this study for the diagnostics of
magnetic fields in the solar atmosphere using hydrogen lines.

---------------------------------------------------------
Title: Scattering polarization of hydrogen lines in the presence of
turbulent electric fields
Authors: Casini, R.; Manso Sainz, R.
2006JPhB...39.3241C Altcode: 2005astro.ph.11148C
We study the broadband polarization of hydrogen lines produced by
scattering of radiation, in the presence of isotropic electric
fields. In this paper, we focus on two distinct problems: (a)
the possibility of detecting the presence of turbulent electric
fields by polarimetric methods and (b) the influence of such fields
on the polarization due to a macroscopic, deterministic magnetic
field. We found that isotropic electric fields decrease the degree
of linear polarization in the scattered radiation, with respect to
the zero-field case. On the other hand, a distribution of isotropic
electric fields superimposed onto a deterministic magnetic field can
increase significantly the degree of magnetic-induced, net circular
polarization. This phenomenon has important implications for the
diagnostics of magnetic fields in plasmas using hydrogen lines,
because of the ubiquitous presence of the Holtsmark microscopic
electric field from neighbouring ions. In particular, previous solar
magnetographic studies of the Balmer lines of hydrogen may need to be
revised because they neglected the effect of turbulent electric fields
on the polarization signals. In this work, we give explicit results
for the Lyman α and Balmer α lines.

---------------------------------------------------------
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-1, 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: Line Formation Theory for the Multiterm Atom with Hyperfine
Structure in a Magnetic Field
Authors: Casini, R.; Manso Sainz, R.
2005ApJ...624.1025C Altcode:
Within the framework of the quantum theory of polarized line
formation, in the limit of complete frequency redistribution and of
the collisionless regime, we derive explicit formulae describing the
statistical equilibrium and the radiative emission of a multiterm
atom with hyperfine structure, in the presence of an external
magnetic field. The formulae we obtained for the radiative rates
of the statistical equilibrium equations and for the radiative
coefficients of the transfer equation for polarized radiation can be
applied to investigate the formation of spectral lines for which both
fine-structure and hyperfine-structure effects are important (e.g.,
the D1 and D2 lines of Na I in the solar atmosphere).

---------------------------------------------------------
Title: Shocks in the Quiet Solar Photosphere: A Rather Common
Occurrence
Authors: Socas-Navarro, H.; Manso Sainz, R.
2005ApJ...620L..71S Altcode: 2004astro.ph.10568S
We present observations of the quiet solar photosphere in the Fe
I lines at 6302 Å where at least four different spatial locations
exhibit upward-directed supersonic flows. These upflows can only be
detected in the circular polarization profiles as a double-peaked
structure in the blue lobe of both Fe I lines. We have detected cases
of either magnetic polarity in the data. The polarization signals
associated with the upflows are very weak, which is probably why they
had not been seen before in this type of observation. We propose that
the observed flows are the signature of aborted convective collapse,
similar to the case reported by Bellot Rubio et al. Our data indicate
that this phenomenon occurs frequently in the quiet Sun, which means
that many magnetic elements (although the fraction is still unknown)
are destroyed even before they are formed completely. The spectral
signatures of supersonic upflows reported here are probably present
in most spectropolarimetric observations of sufficient signal-to-noise
ratio and spatial resolution.

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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 a5F-y5Fo 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.

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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.

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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 2D3/2 ,
5/2 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.

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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

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Title: Towards the Understanding of the Second Solar Spectrum of Ti I
Authors: Manso Sainz, R.; Landi Degl'Innocenti, E.
2003ASPC..307..425M Altcode:
No abstract at ADS

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Title: A qualitative interpretation of the second solar spectrum of
Ti I
Authors: Manso Sainz, R.; Landi Degl'Innocenti, E.
2002A&A...394.1093M Altcode:
The first theoretical investigation of the formation of the linearly
polarized solar line spectrum of a complex atom, neutral titanium, is
presented. The process of formation of line polarization is modeled by
simply considering a plane-parallel layer of Ti I atoms illuminated
from below by the photospheric radiation field, and accounting for
the differential pumping induced in the various magnetic sublevels
by the anisotropic radiation field. The calculated line polarization
pattern is in good qualitative agreement with reported observations,
thus showing that the generation of population imbalances between
magnetic sublevels due to the radiation field anisotropy is the basic
physical mechanism responsible for the observed polarization pattern
in the Fraunhofer spectrum of Ti I. The role of depolarizing collisions
on the polarized spectrum of Ti I is also investigated.

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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.

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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: Polarization by scattering processes and the Hanle effect in
weakly magnetized stellar atmospheres
Authors: Manso Sainz, Rafael
2002PhDT.......308M Altcode:
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: 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

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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, &amp; 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.

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Title: Quiet and Active Granulation Properties
Authors: Manso Sainz, R.; Rodríguez Hidalgo, I.; Collados, M.
1999ASSL..239..197M Altcode: 1999msa..proc..197M
The preliminary results of a classical spectroscopic analysis of a
facular region at mu=0.78 of ~100 arcsec x 50 arcsec are presented. The
variation with magnetic activity of several spectroscopic parameters
has been studied, showing clear evidence that granulation properties
are modified.

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Title: Thermodynamical properties of granulation in active regions.
Authors: Rodríguez Hidalgo, I.; Collados, M.; Manso Sainz, R.;
Barkler, J.
1999joso.proc..195R Altcode:
A two-dimensional spectroscopic study of two solar active regions
is presented. A magnetic filling factor has been defined, and a new
technique to separate large and small spatial scale motions has been
used. Different types of features in the fields of view have been
classified according to their magnetic and convective properties,
and have been analysed with varying magnetic activity.

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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.