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The LLNL Program in Nuclear Structure and Nuclear Astrophysics (NSNA) FY21 Annual Report
Two papers are included in this FY21 Annual Report: ''Evolution of shell structure and collectivity in neutron-rich nuclei'' and ''Investigating nucleosynthesis and the standard model with β decay.
MEASURING THE RADIATIVE PROPERTIES OF ASTROPHYSICAL MATTER USING THE Z MACHINE.
Abstract not provided.
Study of quasi-collisional effects in laboratory and astrophysical plasmas
High-amplitude turbulence excited in plasmas at small-scales can leave imprint on the radiation produced by (accelerated) plasma particles -- mostly electrons in electron-ion plasmas and both electrons and positrons in lepton pair plasmas. Furthermore, turbulence is known to introduce "effective collisional" effects -- anomalous resistivity, dissipation, diffusion, etc. -- in the otherwise collisionless plasmas. These effective collisions affect radiation transfer and modify optical and magneto-optic effects -- the transmittance and reflectivity coefficients, Faraday rotation, etc. Note that the effective collisions considered in this project are not resonant wave-particle interactions, but much less conventional randomization of particles’ paths. Therefore, we colloquially refer them to as "quasi-collisions". The study of quasi-collisions on transport, radiative and optical properties of plasmas is the main focus of this project.
Characterizing charge state distributions in Si and Fe photoionized plasmas to test high density effects in astrophysical code XSTAR.
Abstract not provided.
Z Astrophysical Plasma Properties Collaborations-- Importance and challenges of HED benchmark experiments -.
Abstract not provided.
Testing High Density Effects in Astrophysical Accretion Disk Models with Photoionized Plasma Experiments.
Abstract not provided.
Laboratory Generated Photoionization Fronts Relevant to Astrophysics
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Astrophysical Neutrinos with Future Large Detectors
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A Gateway to Astrophysically Important (n,p) Reactions
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Laboratory Tests of Astrophysical Black Hole Accretion Disk Plasma Models using the Z-machine at SNL
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Probing Astrophysical Collisionless Shocks with Laboratory Experiments
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Laboratory Generated Photoionization Fronts Relevant to Astrophysics
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Opacity of Astrophysical Plasmas
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Red Noise–based False Alarm Thresholds for Astrophysical Periodograms via Whittle’s Approximation to the Likelihood
Astronomers who search for periodic signals using Lomb–Scargle periodograms rely on false alarm level (FAL) estimates to identify statistically significant peaks. Although FALs are often calculated from white noise models, many astronomical time series suffer from red noise. Prewhitening is a statistical technique in which a continuum model is subtracted from the log power spectrum estimate, after which the observer can proceed with a white-noise treatment. Here we present a prewhitening-based method of calculating frequency-dependent FALs. We fit power laws and autoregressive models of order 1 to each Lomb–Scargle periodogram by minimizing the Whittle approximation to the negative log-likelihood (NLL), then calculate FALs based on the best-fit model power spectrum. Our technique is a novel extension of the Whittle NLL to datasets with uneven time sampling. We demonstrate FAL calculations using observations of α Cen B, GJ 581, HD 192310, synthetic data from the radial velocity (RV) fitting challenge, and Kepler observations of a differential rotator. The Kepler data analysis shows that only true rotation signals are detected by red noise FALs, while white noise FALs suggest all spurious peaks in the low-frequency range are significant. A high-frequency sinusoid injected into α Cen B logR$'$ HK observations exceeds the 1% red noise FAL despite having only 8.9% of the power of the dominant rotation signal. In a periodogram of HD 192310 RVs, peaks associated with differential rotation and planets are detected against the 5% red noise FAL without iterative model fitting or subtraction. The software for calculating red noise–based FALs is available on GitHub.