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Polarimetric Studies of the Solar Atmosphere

by Gosain, Sanjay, PhD

Abstract (Summary)
Solar magnetic fields play an important role in the variety of activity phenomena observed on the sun. They are present right from Sun’s deep radiative interior up-to the heliopause. Their evolution, mainly due to photospheric dynamics and flux emergence, leads to activity phenomena like flares, filament eruptions, Coronal Mass Ejections (CMEs). These phenomena directly affect near-Earth space weather by the accompanying high-energy radiation and charged particles. In order to predict these events a detailed understanding of solar magnetic structures is required. Thus, task of measuring solar magnetic fields is of utmost importance in solar physics. However, the measurement of solar magnetic fields is very challenging task. The challenge comes mainly from the fact that the measurements need to be done remotely by sensing the polarization (due to Zeeman effect) of solar spectral lines. Also, the distortions in imaging due to atmospheric “seeing” leads to poor spatial resolution and effects polarization measurements. The focus of this thesis is on the measurement aspects of solar magnetic fields. A new instrument is developed for measuring the vector magnetic fields in the photosphere. The instrument is called Solar Vector Magnetograph (SVM). The key features of the instrument are (i) symmetric imaging optics with no oblique reflections, to minimize instrumental polarization, (ii) a tunable narrow-band imaging filter for scanning the spectral line, which is based on Fabry-Perot etalon, (iii) dual-beam polarization analyzer (Savart Plate), to minimize seeing induced spurious polarization signals, and (iv) a self-developed instrument control software for automated observations. Further, a data-reduction and analysis package with graphical user interface (GUI) is developed for interactive data reduction. The interpretation of observed polarization, i.e., Stokes profiles, in terms of magnetic field vector is done by fitting them with theoretical profiles under Milne-Eddington model atmosphere assumptions. The packages are developed for this purpose as well as for the analysis and visualization of vector magnetograms. Finally, a study of the effect of vector magnetic field parameters on the solar acoustic p-modes is carried out.
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Bibliographical Information:

Advisor:K. Venugopalan and P. Venkatakrishnan

School:Mohan Lal Sukhadia University

School Location:India

Source Type:Doctoral Dissertation

Keywords:Polarimetry, Solar Magnetic Fields, Astronomical Instrumentation, Automation

ISBN:

Date of Publication:06/01/2007

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