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

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 ${\mathrm{d}}^3{\mathrm{\Pi }}_g-{\mathrm{a}}^3{\mathrm{\Pi }}_u$ 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.