Title:
Scaling of collision strengths for highly-excited states of ions of the H- and He-like sequences
Authors:
Fernández-Menchero, L.; Del Zanna, G.; Badnell, N. R.
Affiliation:
AA(Department of Physics, University of Strathclyde, Glasgow, G4 0NG, UK luis.fernandez-menchero@drake.edu; Present address: Department of Physics and Astronomy, Drake University, 2507 University Avenue Des Moines, IA 50311, USA), AB(Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge, CB3 0WA, UK), AC(Department of Physics, University of Strathclyde, Glasgow, G4 0NG, UK)
Publication:
Astronomy & Astrophysics, Volume 592, id.A135, 9 pp. (A&A Homepage)
Publication Date:
08/2016
Origin:
EDP Sciences
Astronomy Keywords:
atomic data, Sun: corona, techniques: spectroscopic
DOI:
10.1051/0004-6361/201628484
Bibliographic Code:
2016A&A...592A.135F
Abstract
Emission lines from highly-excited states (n ? 5) of H- and He-like ions have been
detected in astrophysical sources and fusion plasmas. For such excited states, R-
matrix or distorted wave calculations for electron-impact excitation are very
limited, due to the large size of the atomic basis set needed to describe them.
Calculations for n ? 6 are also not generally available. We study the behaviour of
the electron-impact excitation collision strengths and effective collision strengths
for the most important transitions used to model electron collision dominated
astrophysical plasmas, solar, for example. We investigate the dependence on the
relevant parameters: the principal quantum number n or the nuclear charge Z. We
also estimate the importance of coupling to highly-excited states and the
continuum by comparing the results of different sized calculations. We provide
analytic formulae to calculate the electron-impact excitation collision strengths
and effective collision strengths to highly-excited states (n ? 8) of H- and He-like
ions. These extrapolated effective collision strengths can be used to interpret
astrophysical and fusion plasma via collisional-radiative modelling.
Tables of atomic data for Si xiii and S xv are only available at the CDS via
anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/592/A135