R-matrix electron-impact excitation data for B-like Si and its application in cool stars

Details R-matrix electron-impact excitation data for B-like Si and its application in cool stars R-matrix electron-impact excitation data for B-like Si and its application in cool stars

Jun 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009a%26a...499..943l&link_type=abstract

Astronomy and Astrophysics, Volume 499, Issue 3, 2009, pp.943-954

Astronomy and Astrophysics

Astrophysics

9

Atomic Data, Atomic Processes, Plasmas, Stars: Coronae, X-Rays: Stars, Ultraviolet: Solar System

Scientific paper

We present the results of an intermediate coupling frame-transformation R-matrix calculation for the electron-impact excitation of Si9+. The target and close-coupling expansions are both taken to be the 125 fine-structure levels (58 LS terms) belonging to the configurations 2sx2py (x+y = 3) and 2sα2pβ3l (α+β = 2, l = s, p, and d). Due to the additional resonances included in our calculation, we find significant differences at low temperatures with the widely used n = 2 to 2 excitation rates, also obtained with the R-matrix method, as well as with the n = 2 to 3 excitation rates calculated by using the distorted wave (DW) approximation. We present a list of prominent transition lines and comparisons with SERTS and Hinode/EIS EUV spectra of the solar corona, SUMER observations for the quiet sun, as well as Chandra LETG and Rocket soft X-ray spectra of the Procyon corona and solar flares, respectively. Line emissivities of some transitions are enhanced up to 40% when compared with those obtained from using the previous atomic data at the same electron density (1.6 × 109 cm-3) and temperature (1.3 × 106 K). The comparison with Chandra LETG observation of Procyon reveals that the 3s-2p line flux was significantly underestimated (by a factor of 4-5) in previous analyses. Some EUV and soft X-ray emission line ratios are n_e-sensitive and T_e-insensitive. Estimated electron densities from them shift downwards due to the new resonant-enhanced excitation data used in the present modelling.

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