Open AccessSi x emission lines in spectra obtained with the Solar EUV Rocket Telescope and Spectrograph ( SERTS )
Author(s) -
Keenan F. P.,
O'Shea E.,
Thomas R. J.,
Brosius J. W.,
Katsiyannis A.,
Ryans R. S. I.,
Reid R. H. G.,
Pradhan A. K.,
Zhang H. L.
Publication year - 2000
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.1365-8711.2000.03599.x
Subject(s) - physics , spectral line , extreme ultraviolet lithography , emission spectrum , line (geometry) , spectrograph , electron density , astrophysics , wavelength , telescope , extreme ultraviolet , electron excitation , electron , atomic physics , astronomy , optics , laser , nuclear physics , 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 Si x are presented. These data are subsequently used, in conjunction with recent estimates for proton excitation rates, to derive theoretical electron density sensitive emission‐line ratios involving transitions in the ∼253–356 Å wavelength range. A comparision of these with observations of a solar active region and subflare, obtained during the 1989 flight of the Solar EUV Rocket Telescope and Spectrograph ( SERTS ), reveals that the electron densities determined from most of the Si x line ratios are consistent with one another for both solar features. In addition, the derived densities are also in good agreement with the values of N e estimated from diagnostic lines in other species formed at similar electron temperatures to Si x , such as Fe xii and Fe xiii . These results provide observational support for the general accuracy of the adopted atomic data, and hence line ratio calculations, employed in the present analysis. However, we find that the Si x 256.32‐Å line is blended with the He ii transition at the same wavelength, while the feature at 292.25 Å is not due to Si x , but currently remains unidentified. The intensity of the 253.81‐Å line in the SERTS active region spectrum is about a factor of 3 larger than expected from theory, but the reason for this is unclear, and requires additional observations to explain the discrepancy.