Search

White Dwarfs (WD) are useful across a surprisingly wide range of astrophysical contexts from cosmochronology to piecing together the chemical enrichment history of a galaxy throughout the cycles of star formation to their use as spectrophotometric standards for many major astronomical observatories. In all of these contexts, the fidelity of the information we can extract is predicated on the accuracy of our model atmosphere calculations. Interpretations of actual WD stellar spectral and photometric data depend in one way or another on fits to grids of model atmospheres. The codes used to construct these grids have relied on the basic model of Vidal et al. (1970) (VCS), known as the Unified Theory of line broadening for line shape calculations. There have since been significant advancements in the theory, however, the calculations used in WD model atmospheres have only received minor updates. Meanwhile, continued advances in spectroscopic instrumentation and signal-to-noise of stellar spectral data have uncovered indications of inaccuracies in the VCS theory. The improvements in the fidelity of our data have signaled a simultaneous decline in the fidelity of our spectral fits and fundamental parameter determinations. The inaccuracies manifest as discrepancies in mean mass estimates made using different mass determination techniques. Additionally, fits performed using individual spectral lines as opposed to the entire set of lines Hβ-H8 also yield highly discrepant inferred values for mass and temperature. Motivated by this, Gomez et al. (2016) developed a simulation based line profile calculation code Xenomorph using an improved theoretical treatment of Stark Broadened line profiles themselves. This code made the theoretical line shape advancements available to the WD community for the first time. However, the code required a series of revisions to make it more physically realistic as well as to the numerical methods to make the calculations computationally tractable for the large grids needed for model atmosphere calculations. Comparisons against the standard Tremblay & Bergeron (2009) line shape calculations also demanded an implementation of a simulation based approach to occupation probability. This thesis presents a detailed description of these changes which now make full grids of new and improved line profile calculations feasible and appropriate for use in WD model atmosphere calculations.

Temperature and density measurements of plasmas are important for understanding various phenomena. For example, equations of state, most scaling arguments for Inertial Confinement Fusion and laboratory astrophysics all rely upon accurate knowledge of temperature and density. Spectroscopy is a non-invasive technique to measure these quantities. In this work we establish a new spectroscopic technique by using it to determine temperature. We also compare and contrast the capability of two codes, PrismSPECT and ATOMIC, to infer electron density from experimentally acquired spectra via Stark broadening. We compare and contrast the capability of isoelectronic line ratios and inter-stage line ratios in an absorption spectra to determine electron temperature of a plasma in Local Thermodynamic Equilibrium. The isoelectronic line ratio method has been used previously for experimentally required emission spectra. Stark broadening is often used with a tracer element to diagnose a plasma’s electron density. Our objective is testing quantitatively how well Stark broadening models can predict the plasma density from multiple elements within the same plasma, and whether this is done self-consistently. We measure a transmission spectrum through a ~0.4 $\mu$m Mg-NaF multi-layered foil, tamped with a uniform layer of CH. We use X-rays from the Z facility at Sandia for heating and backlighting. Measurements were acquired in the 7-15$\AA$ range. We found that temperatures inferred from isoelectronic line ratios agree with temperatures inferred from inter-stage line ratios within error. We also found that densities inferred from different elements do not agree when using PrismSPECT, but do agree when using ATOMIC.