Hydrogen Molecules in Supernova Envelopes

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Session 38 -- Supernovae
Display presentation, Thursday, January 13, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[38.06] Hydrogen Molecules in Supernova Envelopes

Michael Culhane and Richard McCray (JILA, U. Colorado, NIST)

The observations of CO and SiO in the infrared spectrum of SN1987A clearly indicate that molecules can form in the debris of a supernova explosion. Since ${\rm H}_2$ is not easily observable we compute its abundance theoretically. For conditions typical of the inner ($v < 2500 {\rm km s}^{-1}$) envelope of SN1987A, the fraction of H that is in molecular form rises to $\sim 1\%$ by $t \sim 800$ d. For $t < 500$ d the formation is dominated by the gas phase reactions ${\rm H} + {\rm H}^+ \rightarrow {\rm H}_2^+ + {\rm h} \nu$; ${\rm H}_2^+ + {\rm H} \rightarrow {\rm H}_2 + {\rm H}^+$. Thereafter, the formation is dominated by the reactions ${\rm H} + {\rm e} \rightarrow {\rm H}^- + {\rm h} \nu$; ${\rm H}^- + {\rm H} \rightarrow {\rm H}_2 + {\rm e}$. At early times the ${\rm H}^-$ may absorb $\sim 10-30\%$ of visible photons, contributing to the apparent paucity of ${\rm H} \alpha$ emission. For $t > 800$ d the abundance of ${\rm H}_2$ ``freezes out'' due to the slowing of all reactions. The opacity of the supernova envelope in the range $912 < \lambda < 1150$ \AA\ is dominated by resonance scattering in the Lyman and Werner bands of ${\rm H}_2$. The resulting fluorescence emission bands of ${\rm H}_2$ in the range $1150 < \lambda < 1650$ \AA\ may be observable in the UV spectra of supernovae at late times.

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