Spectropolarimetry of Fraunhofer Lines in Local Upper Solar Atmosphere

Abstract

Spectropolarimetric results of Fraunhofer lines between 516.3 and 532.6 nm are presented in local upper solar chromosphere and inner corona below a height of about 0.04 solar radius above the solar limb. The data were acquired on 2013 November 3 during a total solar eclipse in Gabon by the prototype Fiber Arrayed Solar Optical Telescope. It is found that the linear polarizations of the Fraunhofer lines in these layers depend strongly on specific spectral lines and positions. A Fraunhofer line at Mg i b _1 518.4 nm can have a polarization amplitude up to 0.36% with respect to the continuum polarization level, while polarizations of lines like Fe i /Cr i 524.7 nm are often merged in the noise level of 6.0 × 10 ^−4 . The polarizations of the Fraunhofer lines, like the emission ones and the continuum, increase with height as a whole trend, and their amplitudes can be close to those of emission ones yielded in close positions, and generally larger than those of the continuum. Rotations of the polarization directions of the Fraunhofer lines are often accompanied by variations in their polarization amplitudes and profile shapes. It is also judged from these polarimetric properties, along with other evidence, that neutral metal atoms exist in these atmospheric layers.

Keywords

• The Sun
• Solar F corona