Laboratory Measurements of the K-shell transition energies in L-shell ions of Si and S

TL;DR

This paper reports highly accurate measurements of K-shell transition energies in silicon and sulfur ions, providing essential data for astrophysical plasma diagnostics and benchmarking atomic theory.

Contribution

It presents the first precise laboratory measurements of these transition energies, improving accuracy beyond previous data and supporting astrophysical observations.

Findings

Measured 18 and 21 X-ray features in silicon and sulfur ions.

Achieved measurement accuracy better than 1 eV.

Validated results against atomic calculations and applied to astrophysical data.

Abstract

We have measured the energies of the strongest 1s-2ell (ell=s,p) transitions in He- through Ne-like silicon and sulfur ions to an accuracy of better than 1eV using Lawrence Livermore National Laboratory's electron beam ion traps, EBIT-I and SuperEBIT, and the NASA/GSFC EBIT Calorimeter Spectrometer (ECS). We identify and measure the energies of 18 and 21 X-ray features from silicon and sulfur, respectively. The results are compared to new Flexible Atomic Code calculations and to semi-relativistic Hartree Fock calculations by Palmeri et al. (2008). These results will be especially useful for wind diagnostics in high mass X-ray binaries, such as Vela X-1 and Cygnus X-1, where high-resolution spectral measurements using Chandra's high energy transmission grating has made it possible to measure Doppler shifts of 100km/s. The accuracy of our measurements is consistent with that needed to analyze Chandra observations, exceeding Chandra's 100km/s limit. Hence, the results presented here not only provide benchmarks for theory, but also accurate rest energies that can be used to determine the bulk motion of material in astrophysical sources. We show the usefulness of our results by applying them to redetermine Doppler shifts from Chandra observations of Vela X-1.