Bibcode
Vitas, N.; Viticchiè, B.; Rutten, R. J.; Vögler, A.
Bibliographical reference
Astronomy and Astrophysics, Volume 499, Issue 1, 2009, pp.301-312
Advertised on:
5
2009
Journal
Citations
26
Refereed citations
19
Description
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 Mn i 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.