Plasma Measurements of the Fe xvii L-shell Emission and Blending with F viii and F ix

• Published in: The Astrophysical journal 2017-11, Vol.850 (1)
• Main Authors: Beiersdorfer, P., Lepson, J. K., Gu, M. F., Bitter, M.
• Format: Article
• Language: English
• Subjects: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; atomic processes; line: formation; stars: coronae; Sun: X-rays, gamma rays; X-rays: general
• ISSN: 1538-4357; 1538-4357

Here, we measured the L-shell emission spectrum of Fe xvii in a low-density, low-gradient magnetically confined laboratory plasma that contains predominately C, O, Fe, and Ni as trace elements and found excellent agreement with the relative spectral emission obtained in solar and astrophysical observations. However, we obtained spectra that appear to have an usually large $1{s}^{2}2{s}^{2}2{p}_{1/2}^{5}3{d}_{3/2}\to 1{s}^{2}2{s}^{2}2{p}^{6}$ Fe xvii resonance transition, which is commonly labeled $3C$, from hot plasmas that also contain fluorine. The wavelength of the Lyα feature of F ix is coincident with the wavelength of the Fe xvii line $3C$ within one part in 538, and its flux, therefore, enhances the Fe xvii resonance line. Moreover, the resonance and forbidden lines of F viii are close to the $3s\to 2p$ transitions in Fe xvii and may further alter the inferred apparent Fe xvii line ratios, particularly in spectrometers with moderate spectral resolution. The enhanced emission of line $3C$ can thus serve as a new spectral diagnostic for the detection of fluorine in astrophysical plasmas.