Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001spie.4498..207m&link_type=abstract
Proc. SPIE Vol. 4498, p. 207-216, UV/EUV and Visible Space Instrumentation for Astronomy and Solar Physics, Oswald H. Siegmund;
Astronomy and Astrophysics
Astronomy
1
Scientific paper
We present here comprehensive experimental data corresponding to helium extreme ultraviolet emission (EUV) for the 300-600A wavelength range in e- + He, H+ + He, and Hnn+ + He (n=2-3) collisions with impact velocities ranging from 1.4 to 6.9 a.u. The degree of linear polarization associated with HeI (1snp) 1Po -> (1s2) 1S decays for n-2-5 ((lambda) =510 to 584A) and HeII (2p) 2Po -> (1s) 2S transitions ((lambda) =304A), have been measured at intermediate and higher energies. These measurements have been conducted using a compact lightweight molybdenum/silicon multilayer mirror (MLM) spetropolarimeter. These experimental results are compared with our most advanced theoretical calculations using the close coupling method and several many body perturbation approaches. In this study, the degree of linear polarization will be discussed as a function of the projectile charge to elucidate few body excitation and ionization-excitation processes. Specifically, more sophisticated calculations including second Born approximation with full off-energy terms for the HeII (2p) 2Po sublevels have been used. The excellent agreement with our HeII Lyman-(alpha) data clearly demonstrates that off-energy terms in two-electron atomic interaction have very prominent effects. Our comprehensive experimental and theoretical database is also of great importance for the understanding of solar physics phenomena. Such results can be used as a new diagnostic tool for clarifying the role of electron and proton beams in solar flares.
Bartchat Klaus
Bray Igor
Bruch Reinhard F.
Fineschi Silvano
Fursa Dmitry V.
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