Soft X-ray emissions of Si IX in Procyon

Abstract

An analysis of $n=3 \to 2$ transition lines of carbon-like silicon reveals that some ratios of line intensities are sensitive to the electron density. The ratio between two group of $3d\to2p$ transition lines at 55.246 \AA and 55.346 \AA is a good $n_{\rm e}$-diagnostic technique, due to its insensitivity to the electron temperature. Using this property, a lower limit of the density of 0.6$\times10^8$cm$^{-3}$ is derived for Procyon, which is consistent with that constrained by C V and Si X emissions. Significant discrepancies in ratios of $3s\to2p$ lines to $3d\to2p$ lines between theoretical predictions and observed values, are found, by the spectral analysis of Procyon observed with the {\it Chandra} High Resolution Transmission Grating spectra. The difference exceeding a factor of 3, cannot be explained by the uncertainty of atomic data. The opacity effect is also not a choice as reported by Ness and co-workers. For the $3s\to2p$ line at 61.611 \AA, present work indicates that the large discrepancy may be due to the contamination from a S VIII line at 61.645 \AA . For the lines at 61.702 and 61.846 \AA, we suggest that the discrepancies may be attributed to contaminations of unknown lines.Comment: 18 pages, 4 figures, accepted by New Astronom

Soft X-ray emissions of highly charged Si vii-Si xii in cool star - Procyon

“…(v) Si viii . The line ratio between 3d–2p (61.022 Å) and 3s–2p (69.646 Å) lines is predicted higher than observation again as revealed in Si ix (Liang & Zhao 2007) and Fe xvi I (and references therein Doron & Behar 2002). The predicted line fluxes at 61.012 and 61.090 Å are slightly overestimated, but agree with observations within 1σ error for Procyon and solar flare observations.…”

“…The line intensity ratio between them is sensitive to the electron density ( n e ), whereas insensitive to the electron temperature ( T e ) with variation less than 3 per cent over log T e (K) = 5.9–6.3 (see fig. 3 in reference Liang & Zhao 2007). The contribution of Si ix to the observed flux at 55.078 Å occupies a considerable part.…”