Spectropolarimetric Diagnostics at the Solar Photosphere near the Limb

Source: arXiv


In the present work, we investigate the formation of Stokes profiles and spectro-polarimetric diagnostics in an active region plage near the limb. We use 3-D radiation-MHD simulations with unipolar fields of an average strength of 400 G, which is largely concentrated in flux tubes in which the field reaches typical kilo-Gauss values. We generate synthetic Stokes spectra by radiative transfer calculations, then we degrade the simulated Stokes signal to account for observational conditions. The synthetic data treated in this manner are compared with and found to roughly reproduce spectro-polarimetric high-resolution observations at Mu=0.39 obtained by the SOUP instrument with the Swedish 1-m Solar Telescope at the beginning of 2006.

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Available from: Suresh Solanki, Aug 18, 2015
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    ABSTRACT: We present high-resolution G-band observations (obtained with the Swedish 1 m Solar Telescope) of the rapid temporal variability of faculae, which occurs on granular timescales. By combining these observations with magnetoconvection simulations of a plage region, we show that much of this variability is not intrinsic to the magnetic field concentrations that are associated with faculae, but rather a phenomenon associated with the normal evolution and splitting of granules. We also show examples of facular variability caused by changes in the magnetic field, with movies of dynamic behavior of the striations that dominate much of the facular appearance at 01 resolution. Examples of these dynamics include merging, splitting, rapid motion, apparent fluting, and possibly swaying.
    The Astrophysical Journal 12/2008; 646(2):1405. DOI:10.1086/505074 · 5.99 Impact Factor
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    ABSTRACT: We present the first center-to-limb G-band images synthesized from high-resolution simulations of solar mag- netoconvection. Toward the limb the simulations show "hilly" granulation with dark bands on the far side, bright granulation walls, and striated faculae, similar to observations. At disk center G-band bright points are flanked by dark lanes. The increased brightness in magnetic elements is due to their lower density compared with the surrounding intergranular medium. One thus sees deeper layers where the temperature is higher. At a given geometric height, the magnetic elements are cooler than the surrounding medium. In the G band, the contrast is further increased by the destruction of CH in the low-density magnetic elements. The optical depth unity surface is very corrugated. Bright granules have their continuum optical depth unity 80 km above the mean surface, the magnetic elements 200-300 km below. The horizontal temperature gradient is especially large next to flux concentrations. When viewed at an angle, the deep magnetic elements' optical surface is hidden by the granules and the bright points are no longer visible, except where the "magnetic valleys" are aligned with the line of sight. Toward the limb, the low density in the strong magnetic elements causes unit line-of-sight optical depth to occur deeper in the granule walls behind than for rays not going through magnetic elements, and variations in the field strength produce a striated appearance in the bright granule walls. Subject headings: convection — magnetic fields — MHD — Sun: faculae, plages — Sun: photosphere
    The Astrophysical Journal 08/2004; 610(2):L137-L140. DOI:10.1086/423305 · 5.99 Impact Factor
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