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Measuring the Magnetic Field in the Sun and the Interstellar Medium

The solar corona and the interstellar medium?two astrophysical plasmas . Why is the coronal B field of interest?. Temperature of corona is 1-2 X 106 KMagnetic fields probably involved via DC currents or MHD wavesAssessment of theories requires measurements. . We know the magnetic field both below and above the corona.

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Measuring the Magnetic Field in the Sun and the Interstellar Medium

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    1. Measuring the Magnetic Field in the Sun and the Interstellar Medium

    2. The solar corona and the interstellar medium…two astrophysical plasmas

    3. Why is the coronal B field of interest? Temperature of corona is 1-2 X 106 K Magnetic fields probably involved via DC currents or MHD waves Assessment of theories requires measurements

    4. We know the magnetic field both below and above the corona

    5. Below: the photosphere. Measurement of the Zeeman Effect

    6. Above the corona: direct magnetometer measurements in the solar wind

    8. How do we measure B in the corona itself?

    9. Radioastronomical propagation measurements

    11. Physics of Faraday Rotation: the cartoon

    12. Physics of Faraday Rotation

    13. The Physics of Faraday Rotation

    14. The Instrument: The Very Large Array Radiotelescope

    15. The Very Large Array

    16. How one measures polarization position angles and Faraday rotation with the VLA Polarization map of a radio galaxy at 1465 MHz

    17. The North Liberty (Iowa) Radio Telescope

    18. The background sources (signal generators for propagation expmts)

    19. Extragalactic sources provide “constellations” of background objects

    20. Measurements in AS826

    21. Measuring the Coronal Magnetic Field from a set of Faraday Rotation Measurements Adopt “forward problem” approach Specify model density function n Specify model B field Iterate to obtain optimum agreement with observations

    22. Plasma Contributions to the Faraday Rotation Integral

    23. Conclusions Measurements consistent with coronal field of 30-80mG at r=6R. (Paetzold et al 1987) Future observations could more effectively constrain the functional form of the coronal magnetic field. Rotation measure changes substantially on timescales of a few hours; too slow to be turbulence. Thus “Mesoscale Plasma Structures”. Smaller, faster fluctuations attributable to waves seen in spacecraft beacon data.

    24. The interstellar medium: another magnetized plasma

    25. Faraday rotation through the ISM

    26. Variation of Faraday Rotation in the Interstellar Medium

    27. What Faraday Rotation Observations have told us about the plasma of the interstellar medium

    28. Conclusions Faraday rotation observations with the VLA can measure the magnetic field in two quite different astrophysical plasmas. These measurements can illuminate the dynamics and thermodynamics of the corona and the interstellar medium

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