Astronomy and Astrophysics – Astrophysics
Scientific paper
Jun 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005a%26a...436l..35o&link_type=abstract
Astronomy and Astrophysics, Volume 436, Issue 2, June III 2005, pp.L35-L38
Astronomy and Astrophysics
Astrophysics
14
Sun: Uv Radiation, Sun: Corona, Sun: Atmosphere
Scientific paper
Using measurements of Mg X 609.78 and 624.94 Å lines from the Coronal Diagnostic Spectrometer (CDS) on board SOHO, we seek to examine the variation of line width and line ratio in regions far off-limb at the Northern pole of the Sun. It is found that above ≈1150´´ the ratio of the two coronal Mg X resonance lines reduces to values that might be expected for a more radiatively dominant excitation mode. A comparison of the line widths with these ratios indicates that the line widths start to show a decrease in their values at the location where the dominant excitation changes from being collisionally to radiatively dominant, that is, at ≈1150´´. We suggest that the decrease in the line widths above ≈1150´´ is likely to be due to a reduction in the non-thermal component of the line widths caused by a damping of upwardly propagating Alfvén waves.
Banerjee Dipti
Doyle Gerry J.
O'Shea Edwin
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