Late-time near-infrared observations of SN 2005df

Tiara Diamond; Peter Hoeflich; Christopher L. Gerardy

doi:10.1088/0004-637X/806/1/107

paper

Late-time near-infrared observations of SN 2005df

arXiv:1410.6759 · doi:10.1088/0004-637X/806/1/107

Abstract

We present late-time ( $200 - 400$ days) near-infrared spectral evolution for the Type Ia supernova SN 2005df. The spectra show numerous strong emission features of [CoII], [CoIII], and [FeII] throughout the $0.8 - 1.8$ μm region. As the spectrum ages, the cobalt features fade as would be expected from the decay of $^{56}$ Co to $^{56}$ Fe. We show that the strong and isolated [FeII] emission line at $1.644$ μm provides a unique tool to analyze near-infrared spectra of Type Ia supernovae. Normalization of spectra to this line allows separation of features produced by stable versus unstable isotopes of iron group elements. We develop a new method of determining the initial central density, $ρ_{c}$ , and the magnetic field, $B$ , of the white dwarf using the width of the $1.644$ μm line. The line width is sensitive because of electron capture in the early stages of burning, which increases as a function of density. The sensitivity of the line width to $B$ increase with time and the effects of the magnetic field shift towards later times with decreasing $ρ_{c}$ . The initial central density for SN 2005df is measured as $ρ_{c} = 0.9 (\pm 0.2)$ (in $1 0^{9}$ g/cm $^{3}$ ), which corresponds to a white dwarf close to the Chandrasekhar mass ( $M_{Ch}$ ) with $M_{WD} = 1.313 (\pm 0.034)$ M $_{⊙}$ and systematic error less than $0.04$ M $_{⊙}$ . Within $M_{Ch}$ explosions, however, the central density found for SN 2005df is very low for a H-accretor, possibly suggesting a helium star companion or a tidally-disrupted white dwarf companion. As an alternative, we suggest mixing of the central region. We find some support for high initial magnetic fields of strength $1 0^{6}$ G for SN 2005df, however, $0$ G cannot be ruled out because of noise in the spectra combined with low $ρ_{c}$ .

arXiv comment13 pages, 14 figures, submitted to ApJ

Late-time near-infrared observations of SN 2005df

Abstract

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