Investigating the Temperature Distribution of Diatomic Carbon in Comets using the Swan Bands

TL;DR

This study analyzes high-resolution spectra of comets to understand the temperature distribution of diatomic carbon (C2) in their comae, revealing a two-temperature model for the Swan bands.

Contribution

It introduces a two-temperature model for C2 in comets based on high-resolution spectral data, advancing understanding of cometary molecular excitation.

Findings

C2 Swan bands are best modeled with two distinct rotational temperatures.

Lower energy lines correspond to a cooler temperature, higher energy lines to a warmer temperature.

The two-temperature distribution has implications for cometary coma physics.

Abstract

We present high spectral-resolution observations of comets 122P/de Vico and 153P/Ikeya-Zhang obtained with the Tull Coud\'{e} spectrograph on the 2.7m Harlan J. Smith telescope of McDonald Observatory. We used these data to study the distribution of the lines of the $\mathrm{d} ^3\Pi_g - \mathrm{a} ^3\Pi_u$ C$_2$ (Swan) bands. We show that the data are best represented with two rotational temperatures, with the lowest energy lines being at a relatively cool temperature and the higher energy lines being at a higher temperature. We discuss the implications of this two temperature distribution and suggest future work.