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Metallicity Effects on
White Dwarf Supernovae

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Contact: F.X.Timmes
my one page vitae,
full vitae,
research statement, and
teaching statement.

On Measuring The Metallicity Of A Type Ia Supernova's Progenitor (2016)
In Type Ia Supernovae (Sne Ia), the relative abundances of chemical elements are affected by the neutron excess in the composition of the progenitor white dwarf. Since these products leave signatures in the spectra near maximum light, spectral features may be used to constrain the composition of the progenitor. In this paper by Miles et al we calculate the nucleosynthetic yields for three SNe Ia simulations, assuming single degenerate, Chandrasekhar mass progenitors, for a wide range of progenitor metallicities, and calculate synthetic light curves and spectra to explore correlations between progenitor metallicity and the strength of spectral features. We use two 2D simulations of the deflagration-detonation-transition scenario with different 56Ni yields and the W7 simulation to control for differences between explosion models and total yields. While the overall yields of intermediate mass elements (16 < A ≤ 40) differ between the three cases, trends in the yields are similar. With increasing metallicity, 28Si yields remain nearly constant, 40Ca yields decline, and Ti and 54Fe yields increase. In the synthetic spectra, we identify two features at 30 days post explosion that appear to deepen with progenitor metallicity: a Ti feature around 4200 Å and a Fe feature around 5200 Å. In all three simulations, their pseudo equivalent widths show a systematic trend with progenitor metallicity. This suggests that these two features may allow differentiation among progenitor metallicities of observed SNe Ia and potentially help reduce the intrinsic Hubble scatter.

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Si & Ti 30 days post-explosion
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Si & Ti 30 days post-explosion
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Si & Ti 30 days post-explosion
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spectra of the DDT-high model for 5 metallicities at 10, 20, 30, and 40 days post-explosion
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spectra at similar 56Ni yields
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knock-out spectra for the DDT-low model with metallicity Z/Z=0.1
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normalized maximum light NUV spectra


On Silicon Group Elements Ejected by Supernovae Type Ia (2014)
The electron fraction is set by the aboriginal composition of the white dwarf and the reactions that occur during the pre-explosive convective burning (see "Changes in Ye during the Simmering Phase" above). To date, determining the makeup of the white dwarf progenitor has relied on indirect proxies, such as the average metallicity of the host stellar population. In this paper by De et al we present analytical calculations supporting the idea that the electron fraction of the progenitor systematically influences the nucleosynthesis of silicon group ejecta in Type Ia supernovae. In particular, we suggest the abundances generated in quasi nuclear statistical equilibrium are preserved during the subsequent freezeout. This allows potential recovery of Ye at explosion from the abundances recovered from an observed spectra. We show that measurement of 28Si, 32S, 40Ca, and 54Fe abundances can be used to construct Ye in the silicon-rich regions of the supernovae. If these four abundances are determined exactly, they are sufficient to recover Ye to 6%. This is because these isotopes dominate the composition of silicon-rich material and iron-rich material in quasi nuclear statistical equilibrium. Analytical analysis shows that the 28Si abundance is insensitive to Ye, the 32S abundance has a nearly linear trend with Ye, and the 40Ca abundance has a nearly quadratic trend with Ye. We verify these trends with post-processing of 1D models and show that these trends are reflected in the model synthetic spectra.

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QSE presevered during freezeout
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Si-Group QSE & post-processeed
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Fe-Group QSE & post-processeed
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Global abundances vs Ye
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Synthetic spectra of W7-like models


Changes in 56Ni from the expansion phase and 22Ne (2009)
Is there a systematic influence of 56Ni from 22Ne during the dynamical expansion phase of a white dwarf supernova? Some suprising answers are offered in Townsley et al. This effort also establishes a framework for exploring systematics effects in a grid of simulations.

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different initial conditions
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a Ye
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changes in 56Ni


Changes in Ye during the Simmering Phase (2008)
Prior to the explosion of a carbon-oxygen white dwarf as a Type Ia supernova in the single-degenerate scenario there is a 100-1000 year simmering phase during which the 12C+12C reaction gradually heats the white dwarf. Chamulak et al and Piro & Bildsten show that weak reactions during this simmering phase set a maximum electron abundance Ye at the time of the explosion.

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flows at ρ=109 g/cc
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changes in Ye
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light curve width changes


On Variations in the Peak Luminosity of Type Ia Supernovae (2003)
Why is there a variation in the peak luminosity of white dwarf supernovae? In this letter we explore how variations in the metallicity of the progenitor main sequence star gives rise to variations in the mass of 56Ni ejected. This effort has motivated several observational searches for the predicted effect.

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birth metallicity vs 56Ni ejected
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distant supernovae
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metallicity scatter at any age