Spectropolarimetry of Fraunhofer lines in local upper solar atmosphere
arxiv(2024)
摘要
Spectropolarimetric results of Fraunhofer lines between 516.3nm and 532.6nm
are presented in local upper solar chromosphere, transition zone and inner
corona below a height of about 0.04 solar radius above the solar limb. The data
were acquired on Nov.3, 2013 during a total solar eclipse in Gabon by the
prototype Fiber Arrayed Solar Optical Telescope(FASOT). It is found that the
polarization amplitudes of the Fraunhofer lines in these layers depend strongly
on specific spectral lines. Fraunhofer line at MgIb_1518.4nm can have a
polarization amplitude up to 0.36% with respective to the continuum
polarization level, while the polarizations of some lines like FeI/CrI524.7nm
and FeI525.0nm are often under the detection limit 6.0× 10^-4. The
polarizations of the Fraunhofer lines, like the emission lines and the
continuum, increase with height as a whole trend. The fractional linear
polarization amplitudes of inner F-corona can be close to those of inner
E-corona, and in general larger than those of inner K-corona. Rotation of the
polarization direction of Fraunhofer line is often accompanied with variations
in their polarization amplitudes and profile shapes. It is also judged from
these polarimetric properties, along with evidences, that neutral atoms exist
in these atmospheric layers. Thus the inner F-corona described here is induced
by the neutral atoms, and the entropy of the inner corona evaluated becomes
larger than those in the underneath layers due to more microstates found.
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