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 $3d\to 2p$ transition lines at 55.246 Åand 55.346 Åis a good $n_{\mathrm{e}}$-diagnostic technique, due to its insensitivity to the electron temperature. Using this property, a lower limit of the density of 0.6$\times 10^8$cm${}^{-3}$ is derived for Procyon, which is consistent with that constrained by C V and Si X emissions. Significant discrepancies in ratios of $3s\to 2p$ lines to $3d\to 2p$ 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 $3s\to 2p$ line at 61.611 Å, present work indicates that the large discrepancy may be due to the contamination from a S VIII line at 61.645 Å. For the lines at 61.702 and 61.846 Å, we suggest that the discrepancies may be attributed to contaminations of unknown lines.

arXiv comment18 pages, 4 figures, accepted by New Astronomy

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Cited by in corpus (1)

• Soft X-ray emissions of highly charged Si VII--Si XII in cool star--Procyon