Open AccessExtreme ultraviolet emission lines of Ar xiv in solar active region and flare spectra
Author(s) -
Keenan F. P.,
Katsiyannis A. C.,
Reid R. H. G.,
Pradhan A. K.,
Zhang H. L.,
Widing K. G.
Publication year - 2003
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-2966.2003.07075.x
Subject(s) - physics , solar flare , spectral line , electron density , spectrograph , line (geometry) , emission spectrum , astrophysics , flare , plasma , electron temperature , atomic physics , extreme ultraviolet , electron , doubly ionized oxygen , ultraviolet , astronomy , optics , nuclear physics , laser , geometry , mathematics
New R‐matrix calculations of electron impact excitation rates for transitions among the 2s 2 2p, 2s2p 2 and 2p 3 levels of Ar xiv are presented. These data are subsequently used to derive the theoretical electron density diagnostic emission‐line intensity ratios R 1 = I (187.95 Å)/ I (194.41 Å) and R 2 = I (257.40 Å)/ I (243.78 Å) for a range of densities ( N e = 10 9 –10 13 cm −3 ) and electron temperatures ( T e = 10 6.3 –10 6.7 K) appropriate to solar transition region and coronal plasmas. A comparison of these diagnostics with observational data for solar active regions and flares, obtained with the Naval Research Laboratory's S082A spectrograph on board Skylab , reveals that the electron densities determined from R 1 are in good agreement with those estimated from line ratios in Fe xiv or Fe xv , which are formed at similar electron temperatures to Ar xiv . However, there are large discrepancies between densities inferred from the R 2 ratio and those from Fe xiv or Fe xv , confirming that the Ar xiv 243.78‐ and 257.40‐ Å lines are badly blended with Fe xv 243.79 Å and Fe xiv 257.38 Å, respectively. Hence, R 2 cannot be employed as a density diagnostic, in contrast to R 1 , which does provide reliable N e estimates.