Astronomy and Astrophysics – Astronomy
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...21012006m&link_type=abstract
American Astronomical Society Meeting 210, #120.06; Bulletin of the American Astronomical Society, Vol. 39, p.245
Astronomy and Astrophysics
Astronomy
2
Scientific paper
Prominence (filament) spines are being analyzed in Hα images from ground-based observatories and in He II 304 Αngstrom (Å) images from the EIT experiment on board the SoHO satellite. Our comparisons show the spines of quiescent prominences are often longer and slightly taller in He II 304Å images than seen in Hα images. Spines are also sharper and more clearly defined in He II 304Å than in Hα images. The prominences (filaments) in some cases appear earlier and can also last longer in 304Å than in Hα. Examples are shown on the disk and above the limb where the spines of separate filaments (prominences) merge in 304Å images before they appear to merge in Hα. In one case, the spine of a quiescent filament disappears in Hα but remains visible in He II images. These observations are consistent with our measurements of a typical quiescent prominence that shows the Hα brightness decreases with height in the prominence, whereas the brightness at He II 304Å slightly increases with height. Thus we find that the spines of quiescent prominences are always more readily visible in 304Å than in Hα. The relative variation of prominence brightness with height reflects a difference in conditions for excitation of these two lines. This is consistent with a presumed increase of temperature with height, in combination with a slight decrease of electron density with height and with the theory that the He II 304Å line is controlled by EUV radiation from the surrounding corona, whereas Hα is influenced by radiation from the chromosphere below. SFM acknowledges support from NSF grant ATM-0519249 and Y.L. from Norwegian Research Council grant FRINAT171012.
Engvold Odbjørn
Lin Yangtin
Martin Sara F.
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