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Author name code: fluri
ADS astronomy entries on 2022-09-14
author:"Fluri, D.M." 

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Title: Polarimetry of Extrasolar Planets
Authors: Berdyugin, A.; Berdyugina, S.; Fluri, D.; Piirola, V.
2011ASPC..449..389B    Altcode:
  Polarimetry is a powerful technique for detecting directly the starlight
  that is scattered in a planetary atmosphere and, thus, possesses
  information on its geometry, chemistry, and thermodynamics. Recently,
  we have started a polarimetric survey of nearby planetary systems
  with hot Jupiters closely orbiting their host stars using the DiPol
  polarimeter at the KVA telescope and the TurPol polarimeter at the
  Nordic Optical Telescope, La Palma. Here we present our first results
  and discuss orbital parameters of the HD 189733 system and scattering
  properties of its planet.

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Title: NLTE modeling of Stokes vector center-to-limb variations in
    the CN violet system
Authors: Shapiro, A. I.; Fluri, D. M.; Berdyugina, S. V.; Bianda,
   M.; Ramelli, R.
2011A&A...529A.139S    Altcode: 2011arXiv1103.2524S
  Context. The solar surface magnetic field is connected with and even
  controls most of the solar activity phenomena. Zeeman effect diagnostics
  allow for measuring only a small fraction of the fractal-like
  structured magnetic field. The remaining hidden magnetic fields can
  only be accessed with the Hanle effect. <BR /> Aims: Molecular lines
  are very convenient for applying the Hanle effect diagnostics thanks
  to the broad range of magnetic sensitivities in a narrow spectral
  region. With the UV version of the Zurich Imaging Polarimeter ZIMPOL II
  installed at the 45 cm telescope of the Istituto Ricerche Solari Locarno
  (IRSOL), we simultaneously observed intensity and linear polarization
  center-to-limb variations in two spectral regions containing the (0,
  0) and (1, 1) bandheads of the CN B<SUP>2</SUP>Σ - X<SUP>2</SUP>Σ
  system. Here we present an analysis of these observations. <BR />
  Methods: We have implemented coherent scattering in molecular lines into
  an NLTE radiative transfer code. A two-step approach was used. First,
  we separately solved the statistical equilibrium equations and compute
  opacities and intensity while neglecting polarization. Then we used
  these quantities as input for calculating scattering polarization and
  the Hanle effect. <BR /> Results: We have found that it is impossible
  to fit the intensity and polarization simultaneously at different
  limb angles in the framework of standard 1D modeling. The atmosphere
  models that provide correct intensity center-to-limb variations fail
  to fit linear polarization center-to-limb variations due to lacking
  radiation-field anisotropy. We had to increase the anisotropy by
  means of a specially introduced free parameter. This allows us to
  successfully interpret our observations. We discuss possible reasons
  for underestimating the anisotropy in the 1D modeling.

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Title: Polarized Reflected Light from the Exoplanet HD189733b:
    First Multicolor Observations and Confirmation of Detection
Authors: Berdyugina, S. V.; Berdyugin, A. V.; Fluri, D. M.; Piirola, V.
2011ApJ...728L...6B    Altcode: 2011arXiv1101.0059B
  We report the first multicolor polarimetric measurements (UBV bands)
  for the hot Jupiter HD189733b and confirm our previously reported
  detection of polarization in the B band. The wavelength dependence of
  polarization indicates the dominance of Rayleigh scattering with a peak
  in the blue B and U bands of ~10<SUP>-4</SUP> ± 10<SUP>-5</SUP> and
  at least a factor of two lower signal in the V band. The Rayleigh-like
  wavelength dependence, also detected in the transmitted light during
  transits, implies a rapid decrease of the polarization signal toward
  longer wavelengths. Therefore, the nondetection by Wiktorowicz,
  based on a measurement integrated within a broad passband covering
  the V band and partly covering the B and R bands, is inconclusive and
  consistent with our detection in B. We discuss possible sources of the
  polarization and demonstrate that effects of incomplete cancellation of
  stellar limb polarization due to starspots or tidal perturbations are
  negligible as compared with scattering polarization in the planetary
  atmosphere. We compare the observations with a Rayleigh-Lambert model
  and determine effective radii and geometrical albedos for different
  wavelengths. We find a close similarity of the wavelength-dependent
  geometrical albedo with that of the Neptune atmosphere, which is known
  to be strongly influenced by Rayleigh and Raman scattering. Our result
  establishes polarimetry as a reliable means for directly studying
  exoplanetary atmospheres.

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Title: Sunspot Umbra Atmosphere from Full Stokes Inversion
Authors: Wenzel, R.; Berdyugina, S. V.; Fluri, D. M.; Arnaud, J.;
   Sainz-Dalda, A.
2010ASPC..428..117W    Altcode: 2010arXiv1003.5114W
  Sunspots are prominent manifestations of the solar cycle and provide
  key constraints for understanding its operation. Also, knowing
  the internal structure of sunspots allows us to gain insights on
  the energy transport in strong magnetic fields and, thus, on the
  processes inside the convection zone, where solar magnetic fields
  are generated and amplified before emerging at the surface on various
  scales, even during solar minima. In this paper, we present results
  of a spectropolarimetric analysis of a sunspot observed during the
  declining phase of solar cycle 23. By inversion of the full Stokes
  spectra, observed in several spectral regions in the optical at the
  THEMIS facility, we infer the height dependence of physical quantities
  such as the temperature and the magnetic field strength for different
  sunspot regions. The simultaneous use of atomic (Fe I 5250.2 and 5250.6
  Å) and highly temperature-sensitive molecular (TiO 7055 Å and MgH
  5200 Å) lines allows us to improve a model of the sunspot umbra.

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Title: Orbital parameters of extrasolar planets derived from
    polarimetry
Authors: Fluri, D. M.; Berdyugina, S. V.
2010A&A...512A..59F    Altcode: 2010arXiv1001.3091F
  Context. Polarimetry of extrasolar planets becomes a new tool for their
  investigation, which requires the development of diagnostic techniques
  and parameter case studies. <BR /> Aims: Our goal is to develop a
  theoretical model which can be applied to interpret polarimetric
  observations of extrasolar planets. Here we present a theoretical
  parameter study that shows the influence of the various involved
  parameters on the polarization curves. Furthermore, we investigate
  the robustness of the fitting procedure. We focus on the diagnostics
  of orbital parameters and the estimation of the scattering radius
  of the planet. <BR /> Methods: We employ the physics of Rayleigh
  scattering to obtain polarization curves of an unresolved extrasolar
  planet. Calculations are made for two cases: (i) assuming an angular
  distribution for the intensity of the scattered light as from a Lambert
  sphere and for polarization as from a Rayleigh-type scatterer; and
  (ii) assuming that both the intensity and polarization of the scattered
  light are distributed according to the Rayleigh law. We show that the
  difference between these two cases is negligible for the shapes of the
  polarization curves. In addition, we take the size of the host star into
  account, which is relevant for hot Jupiters orbiting giant stars. <BR />
  Results: We discuss the influence of the inclination of the planetary
  orbit, the position angle of the ascending node, and the eccentricity
  on the linearly polarized light curves both in Stokes Q/I and U/I. We
  also analyze errors that arise from the assumption of a point-like
  star in numerical modeling of polarization as compared to consistent
  calculations accounting for the finite size of the host star. We find
  that errors due to the point-like star approximation are reduced with
  the size of the orbit, but still amount to about 5% for known hot
  Jupiters. Recovering orbital parameters from simulated data is shown
  to be very robust even for very noisy data because the polarization
  curves react sensitively to changes in the shape and orientation of the
  orbit. <BR /> Conclusions: The proposed model successfully diagnoses
  orbital parameters of extrasolar planets and can also be applied to
  predict polarization curves of known exoplanets. Polarization curves of
  extrasolar planets thus provide an ideal tool to determine parameters
  that are difficult to obtain with other methods, namely inclination
  and position angle of the ascending node of orbits as well as true
  masses of extrasolar planets.

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Title: Nonlinear deconvolution with deblending: a new analyzing
    technique for spectroscopy
Authors: Sennhauser, C.; Berdyugina, S. V.; Fluri, D. M.
2009A&A...507.1711S    Altcode:
  Context: Spectroscopy data in general often deals with an entanglement
  of spectral line properties, especially in the case of blended line
  profiles, independently of how high the quality of the data may be. In
  stellar spectroscopy and spectropolarimetry, where atomic transition
  parameters are usually known, the use of multi-line techniques to
  increase the signal-to-noise ratio of observations has become common
  practice. These methods extract an average line profile by means
  of either least squares deconvolution (LSD) or principle component
  analysis (PCA). However, only a few methods account for the blending
  of line profiles, and when they do, they assume that line profiles
  add linearly. <BR />Aims: We abandon the simplification of linear
  line-adding for Stokes I and present a novel approach that accounts for
  the nonlinearity in blended profiles, also illuminating the process
  of a reasonable deconvolution of a spectrum. Only the combination of
  those two enables us to treat spectral line variables independently,
  constituting our method of nonlinear deconvolution with deblending
  (NDD). The improved interpretation of a common line profile achieved
  compensates for the additional expense in calculation time, especially
  when it comes to the application to (Zeeman) doppler imaging (ZDI). <BR
  />Methods: By examining how absorption lines of different depths
  blend with each other and describing the effects of line-adding in a
  mathematically simple, yet physically meaningful way, we discover how
  it is possible to express a total line depth in terms of a (nonlinear)
  combination of contributing individual components. Thus, we disentangle
  blended line profiles and underlying parameters in a truthful manner
  and strongly increase the reliability of the common line patterns
  retrieved. <BR />Results: By comparing different versions of LSD with
  our NDD technique applied to simulated atomic and molecular intensity
  spectra, we are able to illustrate the improvements provided by our
  method to the interpretation of the recovered mean line profiles. As a
  consequence, it is possible for the first time to retrieve an intrinsic
  line pattern from a molecular band, offering the opportunity to fully
  include them in a NDD-based ZDI. However, we also show that strong
  line broadening deters the existence of a unique solution for heavily
  blended lines such as in molecular bandheads.

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Title: Zeeman-Doppler Imaging of Stellar Magnetic Fields with Atomic
    and Molecular Lines
Authors: Sennhauser, C.; Berdyugina, S. V.; Fluri, D. M.
2009ASPC..405..543S    Altcode:
  We have developed a new code for Zeeman-Doppler Imaging (ZDI)
  of stellar magnetic fields using the Occamian approach for solving
  inverse problems. The inversions are applied to Stokes I and V parameter
  sets obtained by solving the full set of polarized radiative transfer
  equations for both atomic and molecular lines. For the first time we
  demonstrate that molecular polarization strongly constrains the ZDI maps
  and is crucial for obtaining a realistic solution from Stokes I and V
  only observed at a few stellar rotational phases. We also present an
  enhanced LSD technique, which allows analytic separation of blended line
  profiles. The resulting LSD profiles are free from systematic effects
  induced by blends, which are typical for other multi-line techniques.

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Title: Solar Magnetic Field Diagnostics with the Molecular Hanle
    Effect
Authors: Shapiro, A. I.; Fluri, D. M.; Berdyugina, S. V.
2009ASPC..405..343S    Altcode:
  Weak entangled magnetic fields with mixed polarity occupy the main part
  of the quiet solar photosphere. While the Zeeman effect diagnostics
  fail to measure such fields due to cancellation in polarization, the
  Hanle effect, accessible through the second solar spectrum, provides
  us with a very sensitive tool for studying the distribution of weak
  magnetic fields on the Sun. Molecular lines are valuable for magnetic
  field diagnostics thanks to their broad range of magnetic sensitivities
  within narrow spectral regions, so that the differential Hanle effect
  can be employed, which greatly reduces the model dependence of deduced
  magnetic field strengths. Here we present our recent results on the
  diagnostic of solar turbulent magnetic fields with the help of CN
  transitions in the violet system. In addition, we have implemented
  modeling of coherent scattering in molecular lines into a non-LTE
  radiative transfer code. Together with the Hanle effect theory this
  provides us with a realistic model for studying turbulent magnetic
  fields.

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Title: FeH -- A Valuable Magnetic Diagnostic Tool
Authors: Afram, N.; Berdyugina, S. V.; Fluri, D. M.
2009ASPC..405..349A    Altcode:
  Transitions of the FeH molecule are dominating features in the
  near-infrared spectra of sunspots, starspots and red and brown
  dwarfs. Their remarkable magnetic sensitivity provides an excellent
  opportunity to study magnetic fields in these cool objects. However,
  the absence of an adequate theoretical model of the molecule capable
  to reproduce its observed magnetic properties limits the usage of these
  transitions in solar and stellar magnetic studies. Here we present the
  first successful semi-empirical model of the FeH F<SUP>4</SUP>Δ --
  X<SUP>4</SUP>Δ system based on the Hamiltonian for the intermediate
  Hund's case (a-b) and a perturbation from a nearby electronic state,
  resulting in modification of the spin-orbit and spin-spin coupling. Our
  model is able to reproduce the broadening of FeH lines due to the
  Zeeman effect and their polarization signatures detected in sunspots
  and starspots and, for the first time, provides reliable Landé
  factors. This opens a door for developing further applications for
  red and brown dwarfs.

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Title: LSD-a nonlinear approach
Authors: Sennhauser, C.; Berdyugina, S. V.; Fluri, D. M.
2009AIPC.1094..732S    Altcode: 2009csss...15..732S
  Stellar spectra usually are very limited in the signal-to-noise ratio
  (SNR) that can be obtained. In order to increase their informative
  value, different techniques have been developed in the past ten
  years which combine multiple spectral lines by cutting out individual
  line profiles and analysing them by means of least-squares errors or
  PCA. They usually neglect that the bulk of lines are blended, resulting
  in artificial broadening of the retrieved common line pattern, while
  those that care to disentangle blended profiles assume linear line
  adding. <P />Based on the well-known least-squares deconvolution (LSD)
  method, we developed a new technique, which truly accounts for blended
  profiles and deconvolves them in a physically meaningful way by taking
  into account the nonlinearity when abandoning the regime of optically
  thin lines. The so-called interpolation formula by M. Minnaert is
  a unique tool to describe a line profile both in the optically thin
  and the optically thick regime. It enables us to write a total line
  depth in terms of a (nonlinear) combination of contributing individual
  components. <P />Applying different versions of LSD, among them our
  nonlinear (NL-) LSD, to simulated atomic and molecular intensity
  spectra shows the unrivaled functionality of our new method in terms
  of interpretability of the retrieved common line pattern. For the
  first time it is possible to recover an intrinsic line pattern from
  a molecular band.

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Title: Sunspot Model Atmosphere from Inversion of Stokes Profiles
Authors: Wenzel, R.; Berdyugina, V. S.; Fluri, D. M.; Arnaud, J.;
   Sainz Dalda, A.
2008ESPM...12.2.24W    Altcode:
  We present results of a spectropolarimetric analysis of sunspots. By
  inversion of full Stokes spectra observed in serveral spectral regions
  in the optical at the THEMIS facility we infer the height dependence of
  physical quantities such as the temperature, LOS velocity and magnetic
  field for different sunspot regions. The wide spectral range and
  the use of TiO and MgH transitions, which are extremely temperature
  sensitive and can be treated in LTE even in higher layers, allow us
  to extend and improve a sunspot model atmosphere.

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Title: The FeH F<SUP>4</SUP>Δ-X<SUP>4</SUP>Δ system. Creating a
    valuable diagnostic tool to explore solar and stellar magnetic fields
Authors: Afram, N.; Berdyugina, S. V.; Fluri, D. M.; Solanki, S. K.;
   Lagg, A.
2008A&A...482..387A    Altcode:
  Context: Lines of diatomic molecules are ideal tools for studying
  cool stellar atmospheres and the internal structure of sunspots
  and starspots, given their temperature and pressure sensitivities,
  which are typically higher than in atomic lines. The Wing-Ford FeH
  F<SUP>4</SUP>Δ-X<SUP>4</SUP>Δ system represents such a diatomic
  molecule that is, in addition, highly sensitive to magnetic fields. The
  current theoretical description of those transitions that include the
  involved molecular constants, however, are only based on intensity
  measurements because polarimetric observations have not been available
  until now, which limits their diagnostic value. Furthermore, the theory
  has so far been optimized to reproduce energy levels and line strengths
  without taking magnetic sensitivities into account. <BR />Aims: The
  FeH F<SUP>4</SUP>Δ-X<SUP>4</SUP>Δ system is produced by transitions
  between two electronic states with the coupling of the angular momenta
  that is intermediate between limiting Hund's cases (a) and (b). Our goal
  is to investigate the diagnostic capabilities of the current theoretical
  description of the molecule FeH. <BR />Methods: Using the most precise
  available Hamiltonian, we carried out the perturbation calculation
  of the molecular Zeeman effect for this transition and computed the
  Landé factors of the energy levels and of transitions. We extracted
  Landé factors from a comparison of observed and calculated Stokes
  I and V profiles. Certain spectral lines, most frequently with high
  magnetic sensitivity, exhibited discrepancies between the theory and
  observations. We extended the theoretical model with a semi-empirical
  approach to obtain a diagnostic tool that is able to reproduce many
  of the interesting spectral lines. <BR />Results: We find that the
  current theory successfully reproduces the magnetic properties of
  a large number of lines in the FeH F<SUP>4</SUP>Δ-X<SUP>4</SUP>Δ
  system and that the modified Hamiltonian allows us to synthesize
  and successfully reproduce the most sensitive lines. Thus, our
  observations have provided valuable constraints for determining
  empirical molecular constants and Landé factors. <BR />Conclusions:
  The FeH F<SUP>4</SUP>Δ-X<SUP>4</SUP>Δ system is found to be a very
  sensitive magnetic diagnostic tool. Polarimetric data of these lines,
  in contrast to intensity measurements, provide us with more direct
  and detailed information to study the coolest parts of sunspot and
  starspot umbrae, as well as cool active dwarfs.

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Title: First Direct Detection of Magnetic Fields in Starspots and
    Stellar Chromospheres
Authors: Berdyugina, S. V.; Fluri, D. M.; Afram, N.; Suwald, F.;
   Petit, P.; Arnaud, J.; Harrington, D. M.; Kuhn, J. R.
2008ASPC..384..175B    Altcode: 2008csss...14..175B; 2007astro.ph..3559B
  Here we report on the first detection of circular polarization in
  molecular lines formed in cool magnetic regions (starspots) and in
  chromospheric emission lines formed in hot plages on the surfaces
  of active stars. <P />Our survey of G-K-M stars included young
  main-sequence dwarfs and RS~CVn-type giants and subgiants. All
  stars were found to possess surface magnetic fields producing
  Stokes V LSD signals in atomic lines of 0.05% to 0.5%. Several stars
  clearly showed circular polarization in molecular lines of 0.1% to
  1%. The molecular Stokes V signal is reminiscent of that observed in
  sunspots. Chromospheric magnetic fields were detected on most active
  targets in Stokes~V profiles of emission lines with peak polarization
  up to 2%. The observed molecular circular polarization on M dwarfs
  indicates single-polarity magnetic fields covering at least 10% of
  the stellar disk. Smaller signals on K stars imply that their magnetic
  fields are apparently weaker, more entangled than on M dwarfs, or more
  diluted by the bright photosphere.

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Title: First Detection of Polarized Scattered Light from an
    Exoplanetary Atmosphere
Authors: Berdyugina, S. V.; Berdyugin, A. V.; Fluri, D. M.; Piirola, V.
2008ApJ...673L..83B    Altcode: 2007arXiv0712.0193B
  We report the first direct detection of an exoplanet in the visible
  polarized light. The transiting planet HD 189733b is one of the
  very hot Jupiters with shortest periods and, thus, smallest orbits,
  which makes them ideal candidates for polarimetric detections. We
  obtained polarimetric measurements of HD 189733 in the B band well
  distributed over the orbital period and detected two polarization
  maxima near planetary elongations with a peak amplitude of ~2 ×
  10<SUP>-4</SUP>. Assuming Rayleigh scattering, we estimated the
  effective size of the scattering atmosphere (Lambert sphere) to be
  1.5 ± 0.2 R<SUB>J</SUB>, which is 30% larger than the radius of the
  opaque body previously inferred from transits. If the scattering matter
  fills the planetary Roche lobe, the lower limit of the geometrical
  albedo can be estimated as 0.14. The phase dependence of polarization
  indicates that the planetary orbit is oriented almost in a north-south
  direction with a longitude of ascending node Ω = (16° or 196°)
  ± 8°. We obtain independent estimates of the orbit inclination i =
  98° ± 8° and eccentricity e = 0.0 (with an uncertainty of 0.05),
  which are in excellent agreement with values determined previously from
  transits and radial velocities. Our findings clearly demonstrate the
  power of polarimetry and open a new dimension in exploring exoplanetary
  atmospheres even for systems without transits.

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Title: Hanle effect in the CN violet system with LTE modeling
Authors: Shapiro, A. I.; Berdyugina, S. V.; Fluri, D. M.; Stenflo,
   J. O.
2007A&A...475..349S    Altcode: 2007arXiv0709.2515S
  Context: Weak entangled magnetic fields with mixed polarity occupy
  the main part of the quiet Sun. The Zeeman effect diagnostics
  fails to measure such fields because of cancellation in circular
  polarization. However, the Hanle effect diagnostics, accessible through
  the second solar spectrum, provides us with a very sensitive tool for
  studying the distribution of weak magnetic fields on the Sun. <BR
  />Aims: Molecular lines are very strong and even dominate in some
  regions of the second solar spectrum. The CN B {}<SUP>2</SUP> Σ -
  X {}<SUP>2</SUP> Σ system is one of the richest and most promising
  systems for molecular diagnostics and well suited for the application
  of the differential Hanle effect method. The aim is to interpret
  observations of the CN B {}<SUP>2</SUP> Σ - X {}<SUP>2</SUP> Σ system
  using the Hanle effect and to obtain an estimation of the magnetic
  field strength. <BR />Methods: We assume that the CN molecular layer
  is situated above the region where the continuum radiation is formed
  and employ the single-scattering approximation. Together with the
  Hanle effect theory this provides us with a model that can diagnose
  turbulent magnetic fields. <BR />Results: We have succeeded in fitting
  modeled CN lines in several regions of the second solar spectrum to
  observations and obtained a magnetic field strength in the range from
  10-30 G in the upper solar photosphere depending on the considered
  lines. <P />Tables [see full textsee full textsee full textsee full
  text]-[see full textsee full textsee full textsee full text] are only
  available in electronic form at http://www.aanda.org

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Title: A New Mechanism for Polarizing Light from Obscured Stars
Authors: Kuhn, J. R.; Berdyugina, S. V.; Fluri, D. M.; Harrington,
   D. M.; Stenflo, J. O.
2007ApJ...668L..63K    Altcode: 2007arXiv0708.0599K
  Recent spectropolarimetric observations of Herbig Ae/Be stellar systems
  show linear polarization variability with wavelength and epoch near
  their obscured Hα emission. Surprisingly, this polarization is
  not coincident with the Hα emission peak but is variable near the
  absorptive part of the line profile. With a new and novel model, we
  show here that this is evidence of optical pumping-anisotropy of the
  incident radiation that leads to a linear polarization-dependent optical
  depth within the intervening hydrogen wind or disk cloud. This effect
  can yield a larger polarization signal than scattering polarization
  in these systems.

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Title: First polarimetric observations and modeling of the FeH
    F<SUP>4</SUP>Δ-X<SUP>4</SUP>Δ system
Authors: Afram, N.; Berdyugina, S. V.; Fluri, D. M.; Semel, M.;
   Bianda, M.; Ramelli, R.
2007A&A...473L...1A    Altcode: 2007arXiv0708.0298A
  Context: Lines of diatomic molecules are typically much more
  temperature and pressure sensitive than atomic lines, which makes
  them ideal, complementary tools for studying cool stellar atmospheres
  as well as the internal structure of sunspots and starspots. The
  FeH F^4Δ-X^4Δ system represents such an example that exhibits in
  addition a large magnetic field sensitivity. However, the current
  theoretical descriptions of these transitions including the molecular
  constants involved are only based on intensity measurements because
  polarimetric observations have not been available so far, which limits
  their diagnostic value. Furthermore, the theory was optimized to
  reproduce energy levels and line strengths without taking the magnetic
  sensitivities into account. <BR />Aims: We present for the first
  time spectropolarimetric observations of the FeH F^4Δ-X^4Δ system
  measured in sunspots to investigate their diagnostic capabilities for
  probing solar and stellar magnetic fields. In particular, we investigate
  whether the current theoretical model of FeH can reproduce the observed
  Stokes profiles including their magnetic properties. <BR />Methods: The
  polarimetric observations of the FeH F^4Δ-X^4Δ system in Stokes I and
  V are compared with synthetic Stokes profiles modeled with radiative
  transfer calculations. This allows us to infer the temperature and
  the magnetic field strength of the observed sunspots. <BR />Results:
  We find that the current theory successfully reproduces the magnetic
  properties of a large number of lines in the FeH F^4Δ-X^4Δ
  system. In a few cases the observations indicate a larger Zeeman
  splitting than predicted by the theory. There, our observations have
  provided additional constraints, which allowed us to determine empirical
  molecular constants. <BR />Conclusions: The FeH F^4Δ-X^4Δ system is
  found to be a very sensitive magnetic diagnostic tool. Polarimetric
  data of these lines, in contrast to intensity measurements, provide us
  with more direct and detailed information to study the coolest parts
  of sunspot and starspot umbrae, and cool active dwarfs.

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Title: Molecular Hanle effect in the Paschen-Back regime
Authors: Shapiro, A. I.; Fluri, D. M.; Berdyugina, S. V.; Stenflo,
   J. O.
2007A&A...461..339S    Altcode:
  Context: The second solar spectrum resulting from coherent scattering
  is a main tool for diagnostics of turbulent magnetic fields on the
  Sun. Scattering on diatomic molecules plays an important role in
  forming this spectrum and even dominates in some spectral regions. <BR
  />Aims: In a magnetic field electronic states of a molecule are often
  perturbed via the Paschen-Back effect. Sometimes this perturbation
  can completely change the spectrum, not only quantitatively, but
  even qualitatively. Here we calculate molecular scattering properties
  taking into account the Paschen-Back effect. <BR />Methods: Starting
  with the Hund's case (a) wave functions as a basis we obtain with the
  perturbation theory wave functions of the intermediate Hund's case
  (a-b) in a magnetic field. Using new, perturbed values of the Landé
  factors and transition amplitudes we calculate the Mueller matrix
  for coherent scattering at diatomic molecules in the intermediate
  Hund's case (a-b) and look for the effects that can be caused by
  the Paschen-Back effect. <BR />Results: We have found a considerable
  deviation from the Zeeman regime and discuss here the quantitative
  and qualitative effects on observed polarization signals for the CN
  B {}<SUP>2</SUP> Σ - X {}<SUP>2</SUP> Σ and MgH B' {}<SUP>2</SUP>
  Σ - X {}<SUP>2</SUP> Σ systems as examples.

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Title: Molecular Hanle effect in the Paschen-Back regime: theory
    and application
Authors: Shapiro, A. I.; Berdyugina, S. V.; Fluri, D. M.; Stenflo,
   J. O.
2007msfa.conf..317S    Altcode:
  The second solar spectrum resulting from coherent scattering is a main
  tool for diagnostics of turbulent magnetic fields on the Sun. Scattering
  on diatomic molecules plays an important role in forming this spectrum
  and even dominates in some spectral regions. In a magnetic field
  electronic states of a molecule are often perturbed via the Paschen-Back
  effect. Sometimes this perturbation can completely change the spectrum,
  not only quantitatively, but even qualitatively. Here we calculate
  molecular scattering properties taking into account the Paschen-Back
  effect. We calculate the Mueller matrix for coherent scattering at
  diatomic molecules in the intermediate Hund's case (a-b) and look for
  the effects that can be caused by the Paschen-Back effect. We have
  found a considerable deviation from the Zeeman regime and discuss
  here the quantitative and qualitative effects on observed polarization
  signals for the CN B 2 [Sigma] - X 2 [Sigma] system as an example. We
  show an application of the Hanle effect for the interpretation of
  observations of

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Title: Spectro-polarimetry of a sunspot simultaneously in atomic
    and molecular lines.
Authors: Arnaud, J.; Berdyugina, S. V.; Fluri, D. M.; Afram, N.
2007MmSAI..78...89A    Altcode:
  We performed with THEMIS spectro-polarimetric observations
  simultaneously in various atomic and molecular lines. We present the
  observations and discuss an important aspect of spectro-polarimetric
  data reduction: the recentering of the frames in the spectral
  direction needed before substracting spectra to extract polarized
  Stokes parameters. We conclude that THEMIS has the unique capability,
  among present time large solar telescope, of providing polarization
  data almost free from instrumental effects.

---------------------------------------------------------
Title: Spectro-Polarimetry of a Sunspot in Atomic and Molecular
    Lines with THEMIS
Authors: Arnaud, J.; Berdyugina, S. V.; Fluri, D. M.; Afram, N.;
   Solanki, S. K.; Raouafi, N. -E.
2006ASPC..358..319A    Altcode:
  We present spectro-polarimetric observations of a sunspot, which were
  recorded simultaneously with THEMIS in various atomic and molecular
  lines. These observations include the first full Stokes measurements
  of the band-head of TiO around 7055 Å.

---------------------------------------------------------
Title: Molecular Diagnostics of the Internal Structure of Starspots
    and Sunspots
Authors: Afram, N.; Berdyugina, S. V.; Fluri, D. M.; Solanki, S. K.;
   Lagg, A.; Petit, P.; Arnaud, J.
2006ASPC..358..375A    Altcode:
  We have analyzed the usefulness of molecules as a diagnostic tool for
  studying solar and stellar magnetism with the molecular Zeeman and
  Paschen-Back effects. In the first part we concentrate on molecules
  that are observed in sunspots such as MgH and TiO. We present calculated
  molecular line profiles obtained by assuming magnetic fields of 2-3 kG
  and compare these synthetic Stokes profiles with spectro-polarimetric
  observations in sunspots. The good agreement between the theory and
  observations allows us to turn our attention in the second part to
  starspots to gain insight into their internal structure. We investigate
  the temperature range in which the selected molecules can serve as
  indicators for magnetic fields on highly active cool stars and compare
  synthetic Stokes profiles with our recent observations.

---------------------------------------------------------
Title: The Molecular Paschen-Back Effect
Authors: Berdyugina, S. V.; Fluri, D. M.; Solanki, S. K.
2006ASPC..358..329B    Altcode:
  The molecular Paschen-Back effect (PBE) lacks a detailed description
  since the problem was first addressed by Hill in 1929. However,
  many diatomic molecules exhibit the PBE at field strengths typical of
  sunspots and active cool stars. Recently we have presented a complete
  theoretical description of the molecular PBE in Hund's cases (a), (b),
  and all intermediate cases. This description allows us to compute the
  splitting of levels of any multiplicity and the transitions between
  them. We find that in the partial PBE regime strongly asymmetric
  Stokes profiles are produced, whose strengths and asymmetries depend
  sensitively on the magnetic field. Also, the strength of the forbidden
  and satellite transitions increases rapidly with field strength,
  while the strength of the main branch transitions decreases. These
  signatures hold promise to form the basis of new diagnostics of solar
  and stellar magnetic fields.

---------------------------------------------------------
Title: Polarized Scattering in Strong Chromospheric Lines: Theory
    and Its Confrontation with Observations
Authors: Fluri, D. M.; Holzreuter, R.; Stenflo, J. O.
2006ASPC..358..237F    Altcode:
  We present the current status of modeling scattering polarization in
  strong lines and compare it to observations. First, we discuss how the
  emergent polarization profile depends directly on the source function
  gradient and the anisotropy of the radiation field. This explains
  naturally the formation of the triplet peak structure often observed
  in these strong lines. Then, we investigate the Ca II K line which is
  of particular interest since it forms high in the chromosphere. The
  degree of its scattering polarization depends sensitively on atmospheric
  properties and even provides observational evidence for the presence of
  cool components in the chromosphere. Therefore, polarized scattering
  in Ca II K might provide a long searched for, second observational
  tool (apart from CO molecules) to access the coolest parts of the
  chromosphere.

---------------------------------------------------------
Title: Detection of the Molecular Zeeman Effect in Circular
    Polarization on Cool Active Stars
Authors: Berdyugina, S. V.; Petit, P.; Fluri, D. M.; Afram, N.;
   Arnaud, J.
2006ASPC..358..381B    Altcode: 2007astro.ph..3560B
  We report on the first ever detection of circular polarization
  in molecular lines forming in magnetic regions on the surfaces
  of active stars. The new observations were obtained with the
  high-resolution spectro-polarimeter ESPaDOnS recently installed at the
  Canada-France-Hawaii Telescope. In July 2005 we carried out a survey
  of 17 G-K-M stars including active main-sequence dwarfs and RS CVn-type
  giants and subgiants. All stars were found to possess surface magnetic
  fields producing average atomic Stokes-V signals of 0.05% to 0.5%. Three
  stars clearly showed circular polarization in molecular lines of 0.5%
  to 1%. The molecular Stokes-V signal is reminiscent of that observed
  in sunspots.

---------------------------------------------------------
Title: Hanle Effect in the Paschen-Back Regime
Authors: Shapiro, A. I.; Fluri, D. M.; Berdyugina, S. V.; Stenflo,
   J. O.
2006ASPC..358..311S    Altcode:
  The second solar spectrum resulting from coherent scattering is an
  important tool for the diagnostics of turbulent magnetic fields on
  the Sun. Molecular scattering plays an important role in forming this
  spectrum, and even dominates in some spectral regions. We present
  a theory that allows us to calculate the Mueller matrix for coherent
  scattering from diatomic molecules in Hund's intermediate coupling case
  (a-b) for arbitrary molecular transitions. We performed the calculation
  of the molecular Hanle effect in the Paschen-Back regime. We found
  significant differences from the Zeeman regime, and as an example we
  discuss here, both qualitatively and quantitatively, the effects on
  observed polarization signals for the CN violet system.

---------------------------------------------------------
Title: First Polarimetric Measurements and Modeling of the
    Paschen-Back Effect in CaH Transitions
Authors: Berdyugina, S. V.; Fluri, D. M.; Ramelli, R.; Bianda, M.;
   Gisler, D.; Stenflo, J. O.
2006ApJ...649L..49B    Altcode: 2006astro.ph.10588B
  We report the first spectropolarimetric observations and modeling of CaH
  transitions in sunspots. We have detected strong polarization signals in
  many CaH lines from the A-X system, and we provide the first successful
  fit to the observed Stokes profiles using the previously developed
  theory of the Paschen-Back effect in arbitrary electronic states of
  diatomic molecules and polarized radiative transfer in molecular lines
  in stellar atmospheres. We analyze the CaH Stokes profiles together
  with quasi-simultaneous observations in TiO bands and conclude that
  CaH provides a valuable diagnostic of magnetic fields in sunspots,
  starspots, cool stars, and brown dwarfs.

---------------------------------------------------------
Title: Ca II K polarization as a diagnostic of temperature bifurcation
Authors: Holzreuter, R.; Fluri, D. M.; Stenflo, J. O.
2006A&A...449L..41H    Altcode:
  Aims.We compute the linearly polarized spectrum of Ca II K caused by
  coherent scattering and exploit the line for chromospheric diagnosis,
  with particular attention to temperature bifurcation, by comparing
  the theory with solar observations.Methods.We numerically solve
  the statistical equilibrium equations and the radiative transfer
  equation taking into account polarized coherent scattering with partial
  frequency redistribution. All calculations are performed in 1D within
  a plane-parallel atmosphere.Results.We find strong evidence of a
  chromospheric temperature bifurcation. This suggests that the linearly
  polarized spectrum of Ca II K might become a valuable tool to study
  cool components and the dynamics of the chromosphere independently of
  observations of molecular CO lines and millimeter and sub-millimeter
  continua.

---------------------------------------------------------
Title: The molecular Zeeman effect and diagnostics of solar and
    stellar magnetic fields. III. Theoretical spectral patterns in the
    Paschen-Back regime
Authors: Berdyugina, S. V.; Braun, P. A.; Fluri, D. M.; Solanki, S. K.
2005A&A...444..947B    Altcode:
  Many diatomic molecules present in the atmospheres of the Sun and cool
  stars exhibit the Paschen-Back effect at field strengths typical of
  sunspots and active cool stars. Here we present a complete theoretical
  description of the molecular Paschen-Back efect in Hund's cases (a),
  (b) and all cases intermediate to them. This description allows
  us to compute the splitting of levels of any multiplicity and the
  transitions between them. We also introduce a generalized description
  of the effective magnetic Landé factor applicable not just in the
  Zeeman regime, but also in the Paschen-Back regime. We find that in
  the regime of the partial Paschen-Back effect strongly asymmetric
  Stokes profiles are produced, whose strengths and asymmetries depend
  sensitively on the magnetic field. In the regime of the complete
  Paschen-Back effect the profiles become symmetric again (although
  they may be strongly shifted). The strength of the forbidden and
  satellite transitions increases rapidly with field strength in the
  partial Paschen-Back regime, while the strength of the main branch
  transitions decreases. These signatures hold promise to form the basis
  of new diagnostics of solar and stellar magnetic fields.

---------------------------------------------------------
Title: Interpretation of Solar and Stellar Activity in terms of
    Dynamo Modes
Authors: Fluri, D. M.; Berdyugina, S. V.
2005ASPC..346..167F    Altcode:
  The magnetic activity on active, cool stars and on the Sun is spatially
  organized on large scales and exhibits cyclic behavior on various
  time scales. In particular, the biggest active regions tend to appear
  mainly at two preferred longitudes on opposite sides. Therefore,
  a physical mechanism has to exist that breaks the axial symmetry
  of the global magnetic field. This implies that in addition to the
  axisymmetric dipole a non-axisymmetric dynamo mode should be excited
  in the Sun. We discuss possible dynamo mode configurations that can
  explain the patterns observed both on stars and the Sun.

---------------------------------------------------------
Title: Scattering polarization in strong chromospheric
    lines. I. Explanation of the triplet peak structure
Authors: Holzreuter, R.; Fluri, D. M.; Stenflo, J. O.
2005A&A...434..713H    Altcode:
  Although the triplet polarization structure of the Na I D2 and Ca I 4227
  Å lines in the second solar spectrum has been known for more than two
  decades, a clear and consistent explanation has been lacking. Here we
  show that the qualitative profile shape may be explained in terms of the
  anisotropy of the radiation field and partial frequency redistribution
  (PRD) effects. The complicated frequency and depth dependence of the
  anisotropy can be understood in terms of simple arguments that involve
  the source function gradient and boundary effects. We show in particular
  that the triplet peak structure of the polarization profile of Na I D2
  has basically the same origin as for the Ca I 4227 Å line. Hyperfine
  structure and lower-level atomic polarization only modify the core
  polarization without altering the overall qualitative features. For our
  calculations we adopt a numerical method that combines the advantages
  of both the classical formalism with integral source function and the
  density-matrix formalism. In a first step, a multi-level, PRD-capable
  MALI code, which solves the statistical equilibrium and the radiative
  transfer equation self-consistently, computes intensity, opacities
  and collision rates. Keeping these quantities fixed, we obtain the
  scattering polarization in a second step by solving the radiative
  transfer equation for the transitions of interest with the classical
  formalism, which assumes a two-level atomic model with unpolarized
  lower level. Quantum interferences and lower-level atomic polarization
  are included in terms of a wavelength dependent polarizability W_2,
  which is independently obtained with the density-matrix formalism.

---------------------------------------------------------
Title: Comparison between KPVT/SPM and SoHO/MDI magnetograms with
    an application to solar irradiance reconstructions
Authors: Wenzler, T.; Solanki, S. K.; Krivova, N. A.; Fluri, D. M.
2004A&A...427.1031W    Altcode:
  To be able to use both space- and ground-based solar magnetograms and
  construct long time series of derived parameters it is important to
  cross-calibrate them so that we can estimate their reliability and
  combine them. Using two different techniques, we compare magnetograms
  as well as continuum images recorded by the Spectropolarimeter (SPM)
  on Kitt Peak and the Michelson Doppler Interferometer (MDI) on board
  SoHO. We find that the result obtained depends on the method used. The
  method we favour gives almost identical umbral and penumbral areas and
  very similar total magnetic fluxes in faculae. The magnetic fluxes in
  umbrae and penumbrae returned by the two instruments, however, differ
  considerably. We also demonstrate that SPM data can be employed to
  reconstruct total solar irradiance variations with almost the same
  accuracy as recently shown for MDI data.

---------------------------------------------------------
Title: Flip-Flops as Observational Signatures of Different Dynamo
    Modes in Cool Stars
Authors: Fluri, D. M.; Berdyugina, S. V.
2004SoPh..224..153F    Altcode: 2005SoPh..224..153F
  Cool, rapidly rotating stars exhibit enhanced magnetic activity
  with cyclic behavior on various time scales. In particular, the
  longitude of the dominant activity region switches quasi-periodically
  by 180<SUP>∘</SUP>, which is known as the "flip-flop" phenomenon. In
  the present paper we introduce a new approach for the interpretation of
  stellar cycles based on light curve modeling with dipole and quadrupole
  dynamo modes. We discuss the observational signatures of different
  combinations of the dynamo modes. The proposed simple model is able
  to reproduce the basic properties of long-term photometric behavior
  of active stars and allows us to study different mechanisms resulting
  in flip-flops.

---------------------------------------------------------
Title: Evidence for the Hanle effect in molecular lines
Authors: Berdyugina, S. V.; Fluri, D. M.
2004A&A...417..775B    Altcode:
  In many wavelength regions molecular lines dominate the second solar
  spectrum that results from coherent scattering. Scattering polarization
  is modified by magnetic fields via the Hanle effect. This allows us to
  explore the magnetic field regime with weak field strengths and mixed
  polarities, which is not seen with the Zeeman effect and thus contains
  complementary information. Molecular lines are particularly well
  suited to diagnose such turbulent fields because they exhibit a broad
  range of magnetic sensitivities within narrow spectral regions. Thus,
  it is possible to employ the technique of the differential Hanle
  effect, i.e. to obtain field strengths by observing polarization
  ratios in various lines. We have identified one R- and one P-triplet
  of C<SUB>2</SUB> at 5140 Å and 5141 Å, respectively, that satisfy
  all conditions to be used in the differential Hanle effect. Based
  on these lines we have developed a model that can diagnose turbulent
  magnetic fields using the Hanle effect. The tool is sensitive over a
  broad range of magnetic field strengths from a few Gauss up to several
  hundred Gauss. This tool has allowed us to find a significant Hanle
  depolarization of C<SUB>2</SUB> lines in quiet Sun observations,
  which corresponds to a magnetic field strength of 15±3 G.

---------------------------------------------------------
Title: First Evidence for the Hanle Effect in Molecular Lines
Authors: Fluri, D. M.; Berdyugina, S. V.
2004IAUS..219..674F    Altcode: 2003IAUS..219E.189F
  Magnetic fields influence and drive the activity in stellar
  atmospheres. In the optical they can be measured via Zeeman and Hanle
  effect which are relevant in different magnetic field regimes and
  thus complement each other. The Zeeman effect is sensitive to the net
  magnetic flux in the resolution element whereas the Hanle effect allows
  to detect weak directed or entangled magnetic fields. On the Sun Hanle
  effect is observed in prominences in strong chromospheric lines as well
  as in many photospheric lines. Especially in the photosphere Hanle
  effect observations have led to a new paradigm of the magnetic field
  structure. There 99 percent of the volume are filled by relatively weak
  entangled fields of the order of a few Gauss to which Zeeman effect
  observations are pracitcally blind but which are clearly detected
  by the Hanle effect. We find that molecular lines are particularly
  well suited for magnetic field diagnostics with the Hanle effect. In
  molecular bands closeby lines with different sensitivities to the
  magnetic field form under very similar conditions and can be observed
  in a single image. Therefore many potential instrumental and physical
  sources of errors can be eliminated.

---------------------------------------------------------
Title: An operator perturbation method for polarized line
    transfer. VI. Generalized PALI method for Hanle effect with partial
    frequency redistribution and collisions
Authors: Fluri, D. M.; Nagendra, K. N.; Frisch, H.
2003A&A...400..303F    Altcode:
  A generalized iteration method is presented to solve the polarized line
  transfer equation for a two-level-atom in an arbitrarily oriented,
  weak magnetic field. The polarized redistribution matrix employed
  accounts self-consistently for collisions as well as the presence of
  a weak magnetic field responsible for the Hanle effect. The proposed
  numerical method of solution is based on a Polarized Approximate Lambda
  Iteration (PALI) method. A Fourier decomposition of the radiation field
  and of the phase matrix with respect to the azimuthal angle reduces
  the complexity of the problem. A generalized core-wing technique is
  proposed, which permits an efficient implementation of the frequency
  domain structure inherent in the polarized redistribution matrix. The
  numerical method is tested for its accuracy and efficiency by comparing
  with the existing methods.

---------------------------------------------------------
Title: Depolarizing lines in the Sun's spectrum
Authors: Fluri, D. M.; Stenflo, J. O.
2003A&A...398..763F    Altcode:
  The majority of all lines in the solar spectrum depolarize the
  continuum. Here we present a theoretical analysis of the depolarizing
  lines. In a parameter survey where we vary the details of line formation
  such as height of formation, we find that absorption and scattering
  lines have entirely different behavior. While the depolarization
  by absorption lines rapidly decreases with increasing height of
  formation, the depolarization by scattering lines increases with
  height of formation. We interpret the results in terms of a simple
  qualitative model that contains the relevant physics and support it
  with quantitative calculations. The main relevant quantities are the
  anisotropy of the radiation field, which varies over the line profile,
  and the probability that a photon undergoes polarized scattering above
  the height where the atmosphere becomes optically thin. For lines with
  intrinsic polarization we find that the coupling between continuum
  and line polarization can be neglected.

---------------------------------------------------------
Title: Numerical Methods for Solving the Polarized Line Transfer
    Equations with Partial Frequency Redistribution
Authors: Nagendra, K. N.; Frisch, H.; Fluri, D. M.
2003ASPC..307..227N    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Radiative Transfer in Na I D<SUB>2</SUB> and D<SUB>1</SUB>
Authors: Fluri, D. M.; Holzreuter, R.; Klement, J.; Stenflo, J. O.
2003ASPC..307..263F    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Radiative transfer with polarized scattering in the magnetized
    solar atmosphere
Authors: Fluri, Dominique Martin
2003PhDT.......147F    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Modelling solar irradiance variations: separate models for
    the network and active region faculae
Authors: Wenzler, T.; Solanki, S. K.; Fluri, D. M.; Frutiger, C.;
   Fligge, M.; Ortiz, A.
2002ESASP.508..231W    Altcode: 2002soho...11..231W
  In order to determine to what extent solar surface magnetism
  affects solar irradiance we need to reconstruct the irradiance from
  magnetograms. This process requires the use of model atmospheres. Here
  we present two model atmospheres describing faculae in active regions
  and the network. The models have been constructed such that they
  reproduce various data sets simultaneously.

---------------------------------------------------------
Title: Depolarizing Lines in the Solar Spectrum
Authors: Fluri, D. M.; Stenflo, J. O.
2001ASPC..236..205F    Altcode: 2001aspt.conf..205F
  No abstract at ADS

---------------------------------------------------------
Title: Continuum polarization and blend lines in the solar spectrum
Authors: Fluri, D. M.; Stenflo, J. O.
1999ASSL..243..171F    Altcode: 1999sopo.conf..171F
  No abstract at ADS

---------------------------------------------------------
Title: Continuum polarization in the solar spectrum
Authors: Fluri, D. M.; Stenflo, J. O.
1999A&A...341..902F    Altcode:
  We present a theoretical study of the continuum polarization due to
  radiative scattering in the visible solar spectrum. The results from
  nine different solar model atmospheres are compared. The center-to-limb
  variation (CLV) as well as the wavelength dependence of the continuum
  polarization are determined, and the sources of the dependence on the
  model atmospheres are identified. The key physical quantities turn out
  to be the scattering coefficient and the temperature gradient in the
  layer where the polarization is formed. A simple analytical function
  that approximates the CLV of the theoretical continuum polarization
  for every wavelength in the visible is found. This is based in first
  approximation on the assumption that the scattering layer producing the
  polarization is optically thin and lies above the layer of formation of
  the continuum intensity. Applications of the analytical function range
  from determinations of the instrumental zero-level of the polarization
  scale to diagnostic work using empirical center-to-limb curves to
  constrain the solar model atmospheres.