What Does It Mean to be a "Depleted" Comet? High Spectral Resolution Observations of the Prototypical Depleted Comet 21P/Giacobini-Zinner from McDonald Observatory

TL;DR

This study uses high-resolution spectral observations of comet 21P/Giacobini-Zinner to analyze its molecular composition, revealing significant depletions in certain species compared to typical comets, and discusses the implications of these depletions.

Contribution

It provides detailed spectral analysis of a depleted comet, clarifying what molecular depletions mean in the context of comet composition and behavior.

Findings

Comet 21P shows strong depletions in C2, C3, CH, and NH2 relative to CN.

All molecular species are present at similar relative line intensities within bands.

Depletions indicate a lower abundance of these species compared to typical comets.

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 coude spectrograph on the 2.7m Harlan J. Smith Telescope of McDonald Observatory. This comet's spectrum shows strong depletions in C$_2$, C$_3$, CH, and NH$_2$ 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.