Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995a%26a...304..551v&link_type=abstract
Astronomy and Astrophysics, v.304, p.551
Astronomy and Astrophysics
Astrophysics
1
Sun: Photosphere, Line: Formation, Line: Profiles
Scientific paper
The profiles of the sodium D and magnesium b lines in the solar spectrum have been observed at different positions across the solar disc using the Fourier Transform Spectrometer on the McMath-Pierce telescope at Kitt Peak. Matching between the profiles in the Doppler cores of the lines in each multiplet at selected positions on the disc confirm the profile coincidences found by Waddell to a high degree of accuracy. This result has been widely accepted as indicating source function equality between the lines in each multiplet at the same physical depth in the atmosphere. A less widely appreciated implication of the data is that the source functions and absorption coefficients are both independent of direction: it is shown that the profile coincidences are incompatible with anisotropic microturbulence. In the sodium D line comparisons, a very small systematic difference is found between the line profiles in that the core of the D_1_ line lies just outside that of its D_2_ partner. This difference is just such as would occur, according to the work of Avrett, if the collisional coupling between the pair of excited states responsible for the D lines is rather weak. A similar small difference between the Mgb_1_ and Mgb_2_ profiles may be present, although the evidence is rather less clear-cut in that case.
Foster D. C.
van Breda Ian G.
Worrall Gordon
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