PG 1159035 is the prototype of the PG 1159 hot (pre)white dwarf pulsators. This important object was observed during the Kepler satellite K2 mission for 69 days in 59 s cadence mode and by the TESS satellite for 25 days in 20 s cadence mode. We present a detailed asteroseismic analysis of those data. We identify a total of 107 frequencies representing 32
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Abstract ℓ = 1 modes, 27 frequencies representing 12ℓ = 2 modes, and eight combination frequencies. The combination frequencies and the modes with very highk values represent new detections. The multiplet structure reveals an average splitting of 4.0 ± 0.4μ Hz forℓ = 1 and 6.8 ± 0.2μ Hz forℓ = 2, indicating a rotation period of 1.4 ± 0.1 days in the region of period formation. In the Fourier transform of the light curve, we find a significant peak at 8.904 ± 0.003μ Hz suggesting a surface rotation period of 1.299 ± 0.002 days. We also present evidence that the observed periods change on timescales shorter than those predicted by current evolutionary models. Our asteroseismic analysis finds an average period spacing forℓ = 1 of 21.28 ± 0.02 s. Theℓ = 2 modes have a mean spacing of 12.97 ± 0.4 s. We performed a detailed asteroseismicmore » 
Abstract White dwarfs (WDs) are useful across a wide range of astrophysical contexts. The appropriate interpretation of their spectra relies on the accuracy of WD atmosphere models. One essential ingredient of atmosphere models is the theory used for the broadening of spectral lines. To date, the models have relied on Vidal et al., known as the unified theory of line broadening (VCS). There have since been advancements in the theory; however, the calculations used in model atmosphere codes have only received minor updates. Meanwhile, advances in instrumentation and data have uncovered indications of inaccuracies: spectroscopic temperatures are roughly 10% higher and spectroscopic masses are roughly 0.1
M _{⊙}higher than their photometric counterparts. The evidence suggests that VCSbased treatments of line profiles may be at least partly responsible. Gomez et al. developed a simulationbased lineprofile code Xenomorph using an improved theoretical treatment that can be used to inform questions around the discrepancy. However, the code required revisions to sufficiently decrease noise for use in model spectra and to make it computationally tractable and physically realistic. In particular, we investigate three additional physical effects that are not captured in the VCS calculations: ion dynamics, higherorder multipole expansion, and an expanded basis set. We alsomore » 
The standard theory of pulsations deals with the frequencies and growth rates of infinitesimal perturbations in a stellar model. Modes which are calculated to be linearly driven should increase their amplitudes exponentially with time; the fact that nearly constant amplitudes are usually observed is evidence that nonlinear mechanisms inhibit the growth of finite amplitude pulsations. Models predict that the mass of DAV convection zones is very sensitive to temperature (i.e., MCZ∝T−90eff) leading to the possibility that even "small amplitude" pulsators may experience significant nonlinear effects. In particular, the outer turning point of finiteamplitude gmode pulsations can vary with the local surface temperature, producing a reflected wave that is slightly out of phase with that required for a standing wave. This can lead to a lack of coherence of the mode and a reduction in its global amplitude. We compute the size of this effect for specific examples and discuss the results in the context of Kepler and K2 observations.

Abstract The Wootton Center for Astrophysical Plasma Properties (WCAPP) is a new center focusing on the spectroscopic properties of stars and accretion disks using “atparameter” experiments. Currently, these experiments use the Xray output of the Z machine at Sandia National Laboratories — the largest Xray source in the world — to heat plasmas to the same conditions (temperature, density, and radiation environment) as those observed in astronomical objects. The experiments include measuring (1) densitydependent opacities of ironpeak elements at solar interior conditions, (2) spectral lines of lowZ elements at white dwarf photospheric conditions, (3) atomic population kinetics of neon in a radiationdominated environment, and (4) resonant Auger destruction (RAD) of silicon at conditions found in accretion disks around supermassive black holes. In particular, we report on recent results of our experiments involving helium at white dwarf photospheric conditions. We present results showing disagreement between inferred electron densities using the Hβ line and the He I 5876 Å line, most likely indicating incompleteness in our modeling of this helium line.

Calculations of line broadening are important for many different applications including plasma diagnostics and opacity calculations. One concern is that lineshape models employ many approximations that are not experimentally validated for most element conditions due to challenges with highfidelity lineshape benchmark experiments. Until such experiments become available, we need to test approximations with abinitio lineshape calculations. There are three primary formalisms to derive an electronbroadening operator: the impact theory (Baranger, Griem), relaxation theory (Fano), and kinetic theories (Zwanzig, Hussey), all of which give different expressions for electron broadening. The impact and relaxation theories approximate the density matrix as factorizeable while the kinetic theory has a more general density matrix. The impact and kinetic theories relate the electron broadening operator to collision amplitudes, while the relaxation theory has a more complicated formula using projection operators. Each theory has a different prediction for the width and shift of spectral lines, which will become apparent in stronglycoupled plasmas. We have made an effort to better understand the approximations and limitations of all of these approaches and to try to reconcile the differences between them. Here, we present the current status of our understanding of the electronbroadening theories and our preliminary attempt to unifymore »