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    ABSTRACT: We report high angular resolution observations of the outer solar corona carried out at 75 MHz from the Gauribidanur Radio Observatory (Long: 77°26′12″ E, Lat: 13°36′12″ N) about 100 km north of Bangalore, India, during the solar eclipse of October 24, 1995. Our main conclusion is that there are structures of angular size ≤ 2.5′ in the outer solar corona at a height of ≈ 0.4 R⊚ above the photosphere.
    Advances in Space Research 07/2013; 25(9):1847–1850.
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    ABSTRACT: Hanle scattering is an important diagnostic tool to study weak solar magnetic fields. Partial frequency redistribution (PRD) is necessary to interpret the linear polarization observed in strong resonance lines. Usually angle-averaged PRD functions are used to analyze linear polarization. However it is established that angle-dependent PRD functions are often necessary to interpret polarization profiles formed in the presence of weak magnetic fields. Our aim is to present an efficient decomposition technique, and the numerical method to solve the concerned angle-dependent line transfer problem. Together with the standard Stokes decomposition technique we employ Fourier expansion over the outgoing azimuth angle to express in a more convenient form, the angle-dependent PRD function for the Hanle effect. It allows the use of angle-dependent frequency domains of Bommier to solve the Hanle transfer problem. Such an approach is self-consistent and accurate compared to a recent approach where angle-averaged frequency domains were used to solve the same problem. We show that it is necessary to incorporate angle-dependent frequency domains instead of angle-averaged frequency domains to solve the Hanle transfer problem accurately, especially for the Stokes U parameter. The importance of using angle-dependent domains has been highlighted by taking the example of Hanle effect in the case of line transfer with vertical magnetic fields in a slab atmosphere. We have also studied the case of polarized line formation when micro-turbulent magnetic fields are present. The difference between angle-averaged and angle-dependent solutions is enhanced by the presence of micro-turbulent fields.
    Journal of Quantitative Spectroscopy and Radiative Transfer 04/2013; 119.
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    ABSTRACT: Software simulators are now widely used in all areas of science, especially in application to astronomical missions: from instrument design to mission planning, and to data interpretation. We present a simulator to model the diffuse ultraviolet sky, where the different contributors are separately calculated and added together to produce a sky image of the size specified by the instrument requirements. Each of the contributors to the background, instrumental dark current, airglow, zodiacal light and diffuse Galactic light, depends on different factors. Airglow is dependent on the time of day; zodiacal light depends on the time of year, angle from the Sun and from the ecliptic; diffuse UV emission depends on the line of sight. To provide a full description of the sky along any line of sight, we have also added stars. The UV background light can dominate in many areas of the sky and severely limit viewing directions due to overbrightness. The simulator, available as a downloadable package and as a web-based tool, can be applied to preparation of real space missions and instruments. For demonstration,wepresent the example use for the two near-future UV missions: UVIT instrument on the Indian Astrosat mission and a new proposed wide-field (∼1000 square degrees) transient explorer satellite.
    Astronomy and Computing. 01/2013; 1:46–53.


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