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Title: The spectrum and term analysis of singly ionised nickel
Author: Clear, Christian Philip
ISNI:       0000 0004 8504 5936
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2018
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The analysis and interpretation of modern astrophysical spectra requires accurate atomic energy levels and transition wavelengths. The iron-group elements are of particular importance for stellar and galactic evolution studies, and lines from these elements are found in spectra from a wide variety of astrophysical sources. Existing laboratory atomic data for the iron-group elements is often of poor accuracy or incomplete, with some analyses dating back over fifty years. For many elements, including singly ionised nickel (Ni II), the existing atomic data is insufficient for modern analyses. This thesis details the term analysis of Ni II, which aimed to produce accurate energy level values and transition wavelengths. High resolution spectra of nickel-helium hollow cathode lamps were recorded at Imperial College London and the National Institute for Standards and Technology (NIST, USA) using Fourier transform (FT) spectroscopy. In addition to the newly recorded spectra, two archive spectra from the National Solar Observatory (Kitt Peak, USA) extended the nickel-helium spectrum into the infrared. The FT spectra were further supplemented with the acquisition of grating spectra recorded onto photographic plates at NIST. The total wavenumber range of the FT spectra used in this work extends from 1800 cm-1 in the infra-red to 68000 cm-1 in the vacuum ultraviolet, with grating spectra increasing this range to 130000 cm-1. Spectral linelists for the FT and grating spectra were produced. The FT linelist contains the transition wavenumber, signal-to-noise ratio, relative line intensity and full width at half maximum for each observed spectral line. The absolute wavenumber scale for the FT spectra was calculated from 26 singly ionised argon standard lines and gave a calibration accurate to 3 to 5 parts in 10^8, depending on spectral region. The term analysis of 1456 Ni II lines identified in the FT linelist led to the revision of 357 Ni II energy levels. The accuracy of the revised energy levels and transition wavelengths is at least an order of magnitude greater than previously measured values and now meets the accuracy requirements of astrophysicists.
Supervisor: Pickering, Juliet Sponsor: Science and Technology Facilities Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral