Ultraviolet Observations of Comet 96/P Machholz at Perihelion

TL;DR

This study presents ultraviolet spectral observations of Comet 96/P Machholz during perihelion, revealing emission lines, outgassing rates, and comet composition insights using SOHO satellite data.

Contribution

First ultraviolet spectral analysis of Comet 96/P Machholz during perihelion, providing detailed emission data and compositional estimates.

Findings

Detected H I, C II, C III, and O I emissions near the nucleus.

Estimated outgassing rate consistent with extrapolated values.

Found a C to H2O ratio similar to other comets, indicating low carbon abundance does not explain optical anomalies.

Abstract

Ultraviolet spectra of Comet 96/P Machholz were obtained during its 2002 perihelion with the UVCS instrument aboard the SOHO satellite. Emission from H I, C II, C III, and O I, is detected near the nucleus. The outgassing rate is in line with the value extrapolated from rates at larger distances from the Sun, and abundances of C and O are estimated. Reconstructed images show a nearly spherical cloud in H I Ly$\alpha$ emission and an ion tail seen in C III. Radiation pressure on the hydrogen atoms produces a modest distortion of the shape of the Ly$\alpha$ cloud as seen from SOHO, and it produces Doppler shifts up to 30 km s$^{-1}$ in the outer parts of the cloud. We estimate a ratio of C to H$_2$O similar to what is observed in other comets, so low carbon abundance does not account for the anomalously low C$_2$ and C$_3$ ratios to NH$_2$ observed at optical wavelengths.