What does it mean to be a "depleted" comet? High spectral resolution observations of the prototypical depleted comet 21P/giacobini-zinner from the McDonald Observatory

Abstract

We present high spectral resolution optical observations of comet 21P/Giacobini-Zinner from six nights in 2018. The observations were obtained with the Tull Coudé Spectrograph on the 2.7 m Harlan J. Smith Telescope of the McDonald Observatory. This comet's spectrum shows strong depletions in C2, C33, CH, and NH2 relative to CN. We explore what it means for a comet to be depleted and show that all of the species are present in the spectrum at similar relative line intensities within a a molecular band compared with a typical comet. The depletions represent a much lower abundance of the species studied.