The Unusual Spectrum of Comet 96P/Machholz

TL;DR

This study presents spectral observations of comet 96P/Machholz revealing an unusually carbon-poor composition with specific gas production rates, highlighting its distinct chemical profile among comets.

Contribution

First detailed spectral analysis of comet 96P/Machholz showing extreme carbon depletion and unique chemical characteristics.

Findings

Comet 96P/Machholz is extremely carbon poor.

Detected strong NH_2 emission but no CN emission.

Gas production rates for NH, NH_2, and C_2 quantified.

Abstract

We report spectra from 3000-5900 A for comet 96P/Machholz, obtained on 2007 Apr 27 UT with the 3-m Shane telescope at Lick Observatory. The spectra are extremely carbon poor, and show a prominent NH_2 series, but no CN emission. NH, NH_2, and C_2 gas production rates are (8.36 +/- 2.18)x10^25, (29.88 +/- 3.66)x10^25, and (4.52 +/- 0.61)x10^23 molecules sec^-1, respectively, as determined from Haser model fits to the data. Upper limits to the gas production rates for CN and C_3 are 7.5x10^22 and 2.0x10^23, respectively. Though 96P is depleted in C_2 and C_3 relative to NH, it is even more depleted in CN than other so-called "carbon-chain depleted" comets.