XII CANARY ISLANDS WINTER SCHOOL OF ASTROPHYSICS

"ASTROPHYSICAL SPECTROPOLARIMETRY"

Instituto de Astrofísica de Canarias
Puerto de la Cruz, Tenerife, Canary Islands (Spain)
November 13th - 24th, 2000

Programme

Spectropolarimetry of Quasars and Radio Galaxies
Prof. R. Antonucci, U. C. Santa Barbara, USA

Polarization of Accretion Disks and Compact Objects
Prof. R. Blandford, California Institute of Technology, USA

Polarization of Astronomical Masers: Theory, Observations and Modelling
Prof. M. Elitzur, Univ. of Kentucky, USA

Interstellar Magnetic Fields and Infrared-Submillimeter Spectropolarimetry
Prof. R. Hildebrand, Univ. of Chicago, USA

Instrumentation for Astrophysical Spectropolarimetry
Dr. C. Keller, National Solar Observatory, USA

The Physics of Polarization
Prof. E. Landi Degl'Innocenti, Univ. of Firenze, Italy

Polarized Radiation Diagnostics of Stellar Magnetic Fields
Dr. G. Mathys, European Southern Observatory, Chile

Polarized Radiation Diagnostics of Solar Magnetic Fields
Prof. J. O. Stenflo, Institute of Astronomy, Zurich, Switzerland
 


Spectropolarimetry of Quasars and Radio Galaxies
Prof. R. Antonucci, U.C. Santa Barbara, USA

1.  Highly polarized quasars and BL Lac objects, physical inferences from the optical and radio core
    data. Superluminal motion and its unification implications.
2.  Radio galaxies.  FRIIs with strong emission lines are hidden quasars; what are optically dull
    FRIIS? What type of engine do they have? What type of engine powers FRI radio galaxies,
    thermal or nonthermal? Do those classes connote accretion vs rotation power?

3.  Some practical observing considerations:  SNR, subtle systematic errors in the data, interstellar
     foreground polarization.  Sketch of theoretical models of tori and scattering winds.

4.  Spectropolarimetric tests of the optical/UV emission mechanism in quasars - can accretion
    disks be made consistent with the data?

5.  Infrared galaxies, starbursts or AGN?  Definitive evidence from spectropolarimetry for many
    AGN. Active nuclei hidden too deep for detection in the mid-IR, or with ~keV X-rays. First images
    of the obscuring tori, using millimeter interferometers.

Polarization of Accretion Disks and Compact Objects
Prof. R. Blandford, California Institute of Technology, USA
1. Accretion Disks
2. Jets
3. Broad Absorption Line Quasars
4. Magnetars
5. Ergospheres
Polarization of Astronomical Masers: Theory, Observations and Modelling
Prof. M. Elitzur, Univ. of Kentucky, USA
 
Basics of Maser Theory:
        Pumping
        Amplification
        Saturation
        Mode competition

Maser Polarization Theory:

Differences between thermal and maser polarization -- source terms vs polarization rotation
Maser polarization solution for fully resolved Zeeman patterns
Maser polarization solution for overlapping Zeeman components
Circular polarization profiles
Maser Polarization Observations and Modeling:
Star forming regions
AGB stars
Supernova remnants
Interstellar Magnetic Fields and Infrared-Submillimeter Spectropolarimetry
Prof. R. Hildebrand, Univ. of Chicago, USA
1. Introduction to Galactic Magnetic Fields
In this first lecture I will review what we know about magnetic fields in the Milky Way as revealed by observations of polarized starlight, synchrotron emission, Zeeman splitting, Faraday rotation, and emission from magnetically aligned dust grains.  I will discuss the importance of magnetic fields in the structure and evolution of the Galaxy, in containment of cosmic rays, and in formation of stars. I will also introduce the subject of the far-infrared/submillimeter (FIR/SMM) polarization spectrum, to be discussed in detail in the third lecture.
2. Review of Physical Principles Required for Analysis of FIR/SMM Polarimetry
A prerequisite for analysis of far-infrared polarimetry, and especially of far-infrared spectropolarimetry is to understand the relationships between cross sections, emissivities, and polarized emission and absorption. In this lecture I will review these relationships and will briefly discuss the dependence of grain alignment on magnetic torques and other mechanisms.
3. The Far-Infrared Polarization Spectrum
In this lecture I will apply the principles discussed in the second lecture to analysis of the unexpected structure discovered in the FIR/SMM  polarization spectrum. In particular I will discuss the relationship of polarization spectra and flux spectra to cloud structure.
4. Techniques and Principles of Analysis in FIR/SMM Polarimetry
Anyone planning to make polarimetric observations in the far-infrared and submillimeter should understand the techniques and precautions necessary to turn raw data into valid science. In this lecture I will discuss systematic effects, sources of noise, backgrounds, choice of passbands, and the limitations and opportunities for discovering the true structure of a celestial source.
5. Far-Infrared and Sub-Millimeter Polarimetry in the next ten years
In this final lecture I will attempt to look ahead to investigations of magnetic fields over a wide range of length scales with new instruments on the ground, in the stratosphere, and in space.  I will describe several instruments now in construction or in design and will speculate on how they might be used to study the interstellar medium and to determine the role of magnetic fields in galactic structure, cloud structure, and star formation.


Instrumentation for Astrophysical Spectropolarimetry
Dr. C. Keller, National Solar Observatory, USA

1. Principles of polarization measurement
   1.1 Brief history of instruments for spectro-polarimetry
   1.2 Spatial and temporal polarization modulation
   1.3 Statistical errors of polarization measurements
   1.4 Data analysis
2. Optical components for spectro-polarimetry
   2.1 Polaroid-type polarizers
   2.2 Crystal-based polarizers
   2.3 Thin-film polarizers
   2.4 Fixed zero and multiple order retarders
   2.5 Liquid crystal variable retarders
   2.6 Polarized ray-tracing
3. Instrumental errors
   3.1 Polarizing telescopes
   3.2 Angle-dependence of polarizers and retarders, crystal aberrations
   3.3 Wavelength-dependence of polarizers and retarders
   3.4 Detector-induced errors
   3.5 Influence of polarization on photometry and interferometry
4. Spectro-polarimeters for night-time telescopes
   Examples of modern night-time spectro-polarimeters
5. Solar spectro-polarimeters
   5.1 Advanced Stokes Polarimeter
   5.2 Zurich Imaging Stokes Polarimeter
   5.3 SOLIS Vector-Spectromagnetograph


The Physics of Polarization
Prof. E. Landi Degl'Innocenti, Univ. of Firenze, Italy

1. Generalities about Polarization
Description of polarized radiation. The polarization ellipse. Stokes parameters. Properties of the Stokes parameters. Polarization and optical devices. Jones calculus. Mueller matrices. Polarization in reflection and transmission. Fresnel equations. Dichroism and anomalous dispersion. Polarization in everyday life.
2. Mechanisms for the Generation of Polarized Continuum Radiation
Resonance scattering by elementary dipoles. Thompson and Rayleigh scattering. Mie scattering. Polarization by aligned particles. Cyclotron radiation and synchrotron radiation.
3. Mechanisms for the Generation of Polarized Radiation in Spectral Lines
Sketch of the quantum theory and classical analogies. Atomic levels and magnetic sublevels. Atomic populations and coherences. Polarization induced by splittings. Polarization induced by pumping mechanisms. Atomic polarization. Resonance scattering in the two-level atom. Lower level polarization. Relaxation mechanisms.
4. Radiative Transfer Equations for Polarized Radiation
Absorption matrix, stimulated emission matrix, and emission vector. Intrinsic symmetries. Evolution operator. Algebra of 4x4 matrices. Masing action for polarized radiation. Dichroic masers and their   polarization properties.
5. Non-LTE of the 2nd Kind
The density matrix. Statistical equilibrium equations for the density matrix. Coupling of the statistical equilibrium equations and of the radiative transfer equations. Multilevel atoms. Open problems in astrophysical spectropolarimetry.
Polarized Radiation Diagnostics of Stellar Magnetic Fields
Dr. G. Mathys, European Southern Observatory, Chile
1. General framework
Introduction. Zeeman effect. Approximations and limiting cases of interest (quadratic Zeeman effect, Paschen-Back effect, hyperfine structure). Polarized radiative transfer. Approximate solutions (weak lines, weak field). Hydrogen lines. Stellar vs. solar case: disk integration. Rotation and inhomogeneities.
2. Ap stars: the ideal laboratory for stellar magnetic field studies. Instrumentation.
Introduction to Ap stars. First stellar magnetic field detection. Mean longitudinal magnetic field. Integral vs. differential methods. A parenthesis (but an important one): resolved magnetically split lines in Ap stars. General properties of Ap star magnetic fields. Overview of instrumentation.
3. Explotation of line profile information. Linear polarization.
Zeeman Doppler Imaging as a diagnostic tool. The moment technique. LSD. Multiline techniques: two opposite approaches. Linear polarization: the next step. Broad band linear polarimetry. Linear polarization in spectral lines.
4. Polarimetric diagnostics of magnetic fields in non-Ap stars.
Late-type stars and pre-main sequence stars. Early-type stars. White dwarfs: a wide range of regimes.
5. Magnetic geometries and structures. The future.
Stellar magnetic field modelling. Numerical inversion. Alternative approaches. Ap stars nowadays: more complex than ever - but with hints of a general picture.
Future developments. Ap stars: the third dimension. Other nondegenerate stars: magnetic at last. White dwarfs: not so simple after all?
Polarized Radiation Diagnostics of Solar Magnetic Fileds
Prof. J. O. Stenflo, Institute of Astronomy, Zurich, Switzerland
1. The Sun's magnetic field  ---  An introductory overview
1.1. Role of magnetic fields in astrophysics
1.2. Dynamo generation of cosmic magnetic fields
1.3. Sun as a laboratory for magnetoconvection and cosmic dynamos
1.4. Role of magnetic fields for the structuring, dynamics, heating, and instability of the
        solar atmosphere
2. Diagnostic techniques  ---  An introductory overview
2.1. Remote sensing of the Sun: Statement of the inversion problem
2.2. Accessibility of different atmospheric layers
2.3. Formulation of the measurement problem
        2.3.1. Operational definition of the Stokes parameters
        2.3.2. Physical meaning of partial polarization
        2.3.3. Mueller calculus
        2.3.4. Observational obstacles: Instrumental polarization, seeing, flat field, spatial,
                  spectral, and temporal resolutions, photon statistics
2.4. Physical effects producing polarization signatures: Zeeman effect, Hanle effect,
        atomic polarization, impact polarization
3. Zeeman-effect diagnostics
3.1. Observational signatures of the Zeeman effect: Stokes spectra with FTS and
        imaging polarimeters
3.2. Radiative transfer formulation
3.3. Contribution and response functions. Stokes inversion
3.4. Intermittency. Spatially unresolved fields. Multi-component models
3.5. 3-D flux tube models and numerical simulations. Choice of observables.
        Uniqueness problem
4. Hanle diagnostics and coherency effects
4.1. Observational signatures of the Hanle effect with imaging polarimeters
4.2. Complementarity between the Zeeman and Hanle effects. Magnetic parameter
        domains and accessible atmospheric layers
4.3. Extraction of the Hanle depolarization and rotation from the data. Hanle histograms
4.4. Multi-line approach: Differential Hanle effect
4.5. Interpretative models. Uniqueness problem
4.6. Superposition of a polarized continuum. Separation of depolarization and intrinsic
        line polarization
5. Miscellaneous problems. Outlook
5.1. Coronal magnetic fields. Flare physics. Transition-region magnetic fields
5.2. Observations of anomalous polarization effects: Violation of quantum physics?
5.3. Multi-level coherency transfer. Collisional frequency redistribution of mixed quantum
       states
5.4. Numerical radiative transfer tools for efficient polarized radiative transfer
        calculations of the mixed Hanle-Zeeman regime for arbitrary multi-level atoms
5.5. Concluding remarks on the outlook for the future