A brief discussion of the standard theory of line broadening is presented together with an analysis of selected laser-driven implosion experiments. The effect of improved theoretical procedures on experimental analysis is discussed. In particular, we consider the combined effects of ion dynamics and opacity on line profiles used in the analysis of these plasmas. The experiments discussed were performed at the University of Rochester Laboratory for Laser Energetics (LLE). The results presented in this paper illustrate the usefulness of plasma line broadening in diagnosing hot dense plasmas and in understanding fundamental plasma processes.

We briefly describe the analysis of single-site data collected from 1982 to 1992 for the pulsating DB white dwarf GD 358. We show that the amplitudes of almost all of the l = 1 modes change over time, and some of the l = 1 modes disappear for months at a time. We also find a new mode at k = 19, with a frequency of ~1173μHz.

The pulsating DB white dwarf GD 358 was observed by the Whole Earth Telescope (WET) in 1990, 1994, and 2000. While these observing runs revealed a wealth of pulsation modes, they constitute only three “snapshots” of the behavior of this star. These “snapshots” show that GD 358 has a series of l = 1 modes present in the period range of 420 to 810 seconds, with numerous Fourier Transform peaks at the sums and differences of the l = 1 mode frequencies. In addition, the amplitudes of the l = 1 modes and the sum and difference frequency peaks (which I also call “combination peaks” in this paper) are different in each WET run. These data are not sufficient to determine the time scale of the amplitude changes and whether additional l = 1 modes might be present. For this, we need more frequent data sets, although not necessarily WET data.

We propose a pulsation driving mechanism for γ Doradus variable stars. This mechanism requires that the local convective timescale at the base of the envelope convection zone be comparable to or longer than the pulsation period. This mechanism explains both the red and blue edges of the γ Dor instability strip. We predict that some candidate γ Dor stars summarized by Handler (1999) may actually be too hot or too cool to be γ Dor variables.

Several choices exist in the design and production of capsules intended to ignite and propagate fusion burn of the deuterium–tritium (D–T) fuel when imploded by indirect drive at the National Ignition Facility (NIF). These choices include ablator material, ablator dopant concentration and distribution, capsule dimensions, and X-ray drive profile (shock timings and strengths). The choice of ablator material must also include fabrication and material characteristics, such as attainable surface finishes, permeability, strength, transparency to radio frequency and infrared radiation, thermal conductivity, and material homogeneity. Understanding the advantages and/or limitations of these choices is an ongoing effort for LLNL and LANL designers. At this time, simulations in one-, two-, and three-dimensions show that capsules with either a copper-doped beryllium or a polyimide (C22H10N2O4) ablator material have both the least sensitivity to initial surface roughnesses and favorable fabrication qualities. Simulations also indicate the existence of capsule designs based on these ablator materials which ignite and burn when imploded by less than nominal laser performance (900-kJ energy, 250-TW power, producing 250-eV peak radiation temperature). We will describe and compare these reduced-scale capsules, in addition to several designs which use the expected 300-eV peak X-ray drive obtained from operating the NIF laser at 1.3 MJ and 500 TW.

We present the results of a parametric survey of evolutionary models of compositionally stratified white dwarfs with helium surface layers (DB white dwarfs). Because white dwarfs are the most common final end state of stellar evolution, determining their internal structure will offer us many clues about stellar evolution, the physics of matter under extreme conditions, plus the history of star formation and age of the local Galactic disk. As a first step towards determining the internal structure of DB white dwarf stars, we provide a comprehensive set of theoretical g-mode pulsation periods for comparison to observations.

Because DB white dwarfs have a layered structure consisting of a helium layer overlying the carbon/oxygen core, some modes will have the same wavelength as the thickness of the helium layer, allowing a resonance to form. This resonance is called mode trapping (see Brassard et al. 1992 and references therein) and has directly observable consequences, because modes at or near the resonance have eigenfunctions and pulsation periods that are similar to each other. This results in much smaller period spacings between consecutive overtone modes of the same spherical harmonic index than the uniform period spacings seen between non-trapped modes. We demonstrate with an example how one can use the distribution of pulsation periods to determine the total stellar mass, the mass of the helium surface layer, and the extent of the helium/carbon and carbon/oxygen transition zones. With these tools, we have the prospect of being able to determine the structure of the observed DBV white dwarfs, once the requisite observations become available.

We are grateful to C.J. Hansen, S.D. Kawaler, R.E. Nather, and D.E. Winget for their encouragement and many discussions. This research was supported by the National Science Foundation under grants 85-52457 and 90-14655 through the University of Texas and McDonald Observatory.

We report the analysis of 154 hours of nearly continuous high-speed photometric data on the pulsating DB white dwarf (DBV) GD 358 obtained during the Whole Earth Telescope (WET) run of May 1990. The Fourier transform (FT) of the light curve is dominated by power in the range from 1200 – 1700μHz with more than 180 significant peaks in the total transform. We also see significant power at the sums and differences of the dominant frequencies, indicating the importance of nonlinear behavior. We can use this data to obtain an accurate total stellar mass, and surface He layer mass. The implied surface He layer mass, if correct, provides a significant and surprising challenge to stellar evolution theory, as well as the theory of chemical mixing.

White dwarfs are the final end state for the majority of stars, and hold clues to help solve many current pressing astrophysical problems. We can perform asteroseismology on the pulsating white dwarfs to better understand their internal structure and input physics, paving the way to a better understanding of astrophysics, stellar evolution, and the history of our Galaxy. I describe briefly the potential of asteroseismology by using it to infer the internal structure of PG1159-035.

Currently, there are disagreements on the theoretical pulsation properties of DA white dwarf models. Winget and his group (cf Winget 1981, Winget and Fontaine 1982, Winget et al. 1981, 1982) use 0.6M⊙ evolutionary white dwarf models, to find that (Teff)blue is sensitive to the mass of the hydrogen layer and very sensitive to the treatment of convective efficiency. However, (Teff)blue is relatively insensitive to the helium layer mass. Winget and collaborators also find that the hydrogen layer must be restricted to 10−8 > MH/M* > 10−12 for (Teff)blue to occur at ∼ 10,500K in models with ML1 convection (see below). More efficient (ML2) convection pushes the blue edge up to ∼ 12,200K, which is still short of the observed blue edge of ∼ 13,000K.