Abstract
There is a long-standing debate why the Mn i 5394.7 Å line in the solar irradiance spectrum brightens more at higher activity than
other photospheric lines. The claim that this is caused by spectral interlocking to chromospheric emission in the Mg ii h&k lines is
disputed. In this paper we settle this issue, using classical one-dimensional modeling for demonstration and modern three-dimensional
MHD simulation for verification and analysis. The unusual sensitivity of the Mn i 5394.7 Å line to solar activity is due to its excessive
hyperfine structure. This overrides the thermal and granular Doppler smearing through which the other, narrower, photospheric lines
lose such sensitivity.We take the nearby Fe i 5395.2 Å line as example of the latter, and analyze the formation of both lines in detail to
demonstrate and explain the granular Doppler brightening which affects all narrow photospheric lines. Neither the chromosphere nor
Mg ii h&k emission play a role, nor is it correct to describe the activity sensitivity of Mn i 5394.7 Å in terms of plage models with
outward increasing temperature contrast. The Mni 5394.7 Å line represents a proxy diagnostic of strong-field magnetic concentrations
in the deep solar photosphere comparable to the G band and the blue wing of Hα, but not a better one than these. The Mn i lines are
more promising as diagnostics of weak fields in high-resolution Stokes polarimetry.
Original language | Undefined/Unknown |
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Pages (from-to) | 301-312 |
Number of pages | 12 |
Journal | Astronomy and Astrophysics |
Volume | 499 |
Issue number | 1 |
Publication status | Published - 2009 |