Rotational Temperature Modeling of the Swan $Δν= 0$ Band Sequence in Comet 122P/de~Vico

Abstract

We modeled observations of the C$_2$ $\mathrm{d} ^3Π_g - \mathrm{a} ^3Π_u$ (Swan) $Δν= 0$ sequence observed in spectra of comet 122P/de Vico obtained with the 2.7m Harlan J. Smith Telescope and Tull Coude spectrograph of McDonald observatory on 10/03/1995 and 10/04/1995. The data used spanned 4986-5169Åat R=$λ/Δλ$=60,000. We used the PGOPHER molecular spectra model to generate and fit synthetic spectra with the d$^3Π_g$ having one and two rotational temperatures. We found the excited state had a two component rotational temperature, similar to that found for comet Halley. The modeled spectrum was sufficiently high quality that local perturbations were important to include. The large perturbation, b$^3Σ_g^-(ν=10)$, was added to our fits and some new estimates on its molecular constants were found.