Laboratory Measurements of the K-Shell Transition Energies in L-Shell Ions of Si and S

Abstract

We have measured the energies of the strongest 1s-2 ( ) = ℓ ℓ s, p transitions in He-through Ne-like silicon and sulfur ions to an accuracy of <1 eV using the 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 Chandraʼs high-energy transmission grating has made it possible to measure Doppler shifts of -100 km s 1 . The accuracy of our measurements is consistent with that needed to analyze Chandra observations, exceeding Chandraʼs -100 km s 1 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.

Benchmark Experiment for Photoionized Plasma Emission from Accretion-Powered X-Ray Sources

“…The RAD assumption was used to explain why L-shell ion emission was apparently not observed, even though the accretion disk models include these ions. This assumption was later questioned as L-shell ion lines were observed from Vela X-1 and Cygnus X-3 [29][30][31] and based on detailed atomic physics modeling [32][33]. Observational X-ray astronomy has made significant advances since the RAD approximation was first invoked and the spectra appear to be more complex and varied than was initially appreciated.…”

Relativistic MR-MP Energy Levels for L-shell Ions of Sulfur and Argon

“…The recommended energy values in the NIST database for Li-like S XIV and Ar XVI are compared with our MR-MP results in Figure 3. We also included in our comparison previous CI-based calculations (Palmeri et al 2008; Hell et al 2016) as well as the level energies collected in the CHIANTI v8 database (Dere et al 1997; Del Zanna et al 2015). The deviations for these previous calculations are scattered and over 0.5 eV for many levels, including the 1 s 2( s, p ) 2 levels.…”

“…The x -axis corresponds to the index of each level in Tables 9 and 10. Previous calculations are also included for comparison: HFR (Palmeri et al 2008), FAC (Hell et al 2016) and AUTOSTRUCTURE as included in the CHIANTI v8 data base (Dere et al 1997; Del Zanna et al 2015). …”

“…of L-shell ions of S needed for the modeling of astrophysical systems. Multiple spectroscopic techniques have been used, including measurements with the beam-foil technique (Langenberg et al 1980; Yang et al 1980, 2009), lasers (Fawcett et al 1970; Fawcett & Hayes 1973, 1987; Faenov et al 1994), heavy-ion storage rings (Schippers et al 2012) and electron beam ion traps (EBIT) (Lepson & Beiersdorfer 2005; Beiersdorfer et al 2014; Hell et al 2016; Beiersdorfer et al 2017). On the theoretical/computational side, a large body of work has been performed, from systematic calculations of L-shell ions of S (Bhatia & Landi 2003a,b; Karpuškiene˙ et al 2005; Landi & Bathia 2008; Palmeri et al 2008; Luna et al 2009; Martins et al 2009; Fan et al 2009; Liang et al 2011; Pagan et al 2011; Elabidi et al 2012; Li et al 2013; Hell et al 2016) to isoelectronic sequence of various L-shell ions (Witthoeft et al 2007; Jönsson et al 2011; Liang et al 2012; Rynkunb et al 2012; Jönsson et al 2014; Rynkunb et al 2014; Nazé et al 2014; Wang et al 2014, 2015, 2017); see Fan et al (2009) and references therein for a short account of other calculations.…”

“…For few-electron systems (H-, He- and Li-like S and Ar) there are data for many transitions, including K-vacancy levels. In the case of multielectron L-shell ions, Be- to Ne-like S and Ar, the data are limited, and the accuracy is often too poor for astrophysical plasma diagnostics (Hell et al 2016) and laboratory line identification (Lepson et al 2003; Tr¨abert et al 2005; Beiersdorfer et al 2014). The data are particularly limited for K-vacancy levels of multielectron L-shell ions (Hell et al 2016).…”