The changing rotational excitation of C_3 in comet 9P/Tempel 1 during Deep Impact

TL;DR

This study observed the changes in the rotational excitation and production rate of C$_3$ molecules in comet 9P/Tempel 1 during the Deep Impact event, revealing temperature increases and sustained elevated production post-impact.

Contribution

It provides the first detailed analysis of the spatial, spectral, and temporal evolution of C$_3$ excitation and production during a comet impact event.

Findings

Rotational excitation temperature increased from 45K to 61K after impact.

C$_3$ production rate peaked at 1.7 x 10^{23} s^{-1} two hours post-impact.

Excitation temperature returned to pre-impact levels within 4 hours.

Abstract

The 4050\AA\ band of C$_3$ was observed with Keck/HIRES echelle spectrometer during the {\em Deep Impact} encounter. We perform a 2-dimensional analysis of the exposures in order to study the spatial, spectral, and temporal changes in the emission spectrum of C$_3$. The rotational population distribution changes after impact, beginning with an excitation temperature of $\sim$45\,K at impact and increasing for 2\,hr up to a maximum of 61$\pm$5\,K. From 2 to 4 hours after impact, the excitation temperature decreases to the pre-impact value. We measured the quiescent production rate of C$_3$ before the encounter to be 1.0 $\times 10^{23}$ s$^{-1}$, while 2 hours after impact we recorded a peak production rate of 1.7 $\times 10^{23}$ s$^{-1}$. Whereas the excitation temperature returned to the pre-impact value during the observations, the production rate remained elevated, decreasing slowly, until the end of the 4\,hr observations. These results are interpreted in terms of changing gas densities in the coma and short-term changes in the primary chemical production mechanism for C$_{3}$.