Fe XVII $2p$-$3s$ line ratio diagnostic of shock formation radius in O stars

Abstract

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

arXiv comment21 pages, 13 figures

References in corpus (42)

• A Grid of NLTE Line-Blanketed Model Atmospheres of O-type Stars
• A Grid of NLTE Line-Blanketed Model Atmospheres of Early B-type Stars
• The surprising magnetic topology of tauSco: fossil remnant or dynamo output?
• X-Ray Spectroscopy of Stars
• Bright OB stars in the Galaxy - III. Constraints on the radial stratification of the clumping factor in hot star winds from a combined Halpha, IR and radio analysis
• High resolution X-Ray spectroscopy of Zeta Puppis with the XMM-Newton Reflection Grating Spectrometer
• High Resolution Observations of the Elliptical Galaxy NGC 4636 with the Reflection Grating Spectrometer On-Board XMM-Newton
• High Resolution X-Ray Spectra of Capella: Initial Results from the Chandra High Energy Transmission Grating Spectrometer
• Properties of Galactic early-type O-supergiants: A combined FUV-UV and optical analysis
• The Chandra Iron-L X-Ray Line Spectrum of Capella
• Detection of Doppler Shifted X-ray Line Profiles from the Wind of Zeta Puppis (O4f)
• X-Ray Line Profiles from Parameterized Emission Within an Accelerating Stellar Wind
• Inner-shell Absorption Lines of Fe~VI-- Fe~XVI: A Many-body Perturbation Theory Approach
• Modeling the NeIX Triplet Spectral Region of Capella with the Chandra and XMM-Newton Gratings
• High-Resolution {\it Chandra} Spectroscopy of tau Scorpii: A Narrow-Line X-ray Spectrum From a Hot Star
• The X-ray spectrum of Fe XVII revisited with a multi-ion model
• X-ray Emission Line Profile Modeling of O stars: Fitting a Spherically-Symmetric Analytic Wind-Shock Model to the Chandra Spectrum of zeta Puppis
• Measurements and analysis of helium-like triplet ratios in the X-ray spectra of O-type stars
• Lower entropy bounds and particle number fluctuations in a Fermi sea
• Wind signatures in the X-ray emission line profiles of the late O supergiant $\zeta$ Orionis
• A mass-loss rate determination for zeta Puppis from the quantitative analysis of X-ray emission line profiles
• First Application of the Fe XVII I(17.10 A)/I(17.05 A) Line Ratio to Constrain the Plasma Density of a Cosmic X-ray Source
• X-Rays From Massive OB Stars: Thermal Emission From Radiative Shocks
• Influence of Resonances on Spectral Formation of X-Ray Lines in Fe XVII
• Fe XVII X-ray Line Ratios for Accurate Astrophysical Plasma Diagnostics
• Simultaneous X-ray and optical spectroscopy of the Oef supergiant lambda Cep
• X-ray spectra of the Fe-L complex
• A new paradigm for the X-ray emission of O stars from XMM-Newton observations of the O9.7 supergiant zeta Orionis
• A detailed X-ray investigation of ζ Puppis III. A spectral analysis of the whole RGS spectrum
• High Resolution Photoexcitation Measurements Exacerbate the Long-Standing Fe XVII Oscillator Strength Problem
• Breit-Pauli R-matrix calculations for electron impact excitation of Fe XVII: a benchmark study
• Modeling broadband X-ray absorption of massive star winds
• X-ray, UV and optical analysis of supergiants: $\epsilon$ Ori
• Revisiting the Fe XVII line emission problem: laboratory measurements of the 3s-2p and 3d-2p line-formation channels
• Measuring the shock-heating rate in the winds of O stars using X-ray line spectra
• X-ray spectra of the Fe-L complex II: atomic data constraints from EBIT experiment and X-ray grating observations of Capella
• Investigating the origin of cyclical wind variability in hot, massive stars - I. On the dipolar magnetic field hypothesis
• Detectability of small-scale magnetic fields in early-type stars
• XMM-Newton observations of Zeta Orionis (O9.7 Ib): A Collisional Ionization Equilibrium model
• Anomalous X-ray line ratios in the cTTS TW Hya
• Effect of scattering on the transonic solution topology and intrinsic variability of line-driven stellar winds
• High-resolution Charge Exchange Spectra with L-shell Nickel Show Striking Differences from Models

Cited by in corpus (2)

• New Measurement Resolves Key Astrophysical Fe XVII Oscillator Strength Problem
• Testing the Reliability of X-rays as a Tool for Constraining Mass-loss Rates of Hot Stars