Fe xvii 2p–3s Line Ratio Diagnostic of Shock Formation Radius in O Stars

The $2p$-$3s$ lines of Fe XVII in the X-ray spectrum O-type star $\zeta$ Puppis exhibit an anomalous (3G + M2)/(3F) line ratio $\sim$1.4, comparison with $\sim$2.4 for almost all other collisionally excited astrophysical spectra. Based on work Mauche et al. (2001), we conjectured that strong UV field produces observed by depopulation metastable $3s$ states, and can potentially be used as independent diagnostic plasma formation radius. We Flexible Atomic Code (FAC) collisional-radiative model to effect photoexcitation from O stars lines. compared our calculations archival spectra coronal hot Chandra HETGS XMM-Newton RGS benchmark various electron densities intensities. Our show does not produce a sufficiently large dynamic range 3F/(3F 3G M2) fraction explain difference between Pup. Thus, this likely cannot Pup, its origin is still unexplained.