Color variations of Comet C/2013 UQ4 (Catalina)

TL;DR

This study observes rapid color changes in Comet C/2013 UQ4 (Catalina), revealing a chemically heterogeneous dust coma with at least two distinct components, and finds no significant gaseous CO/CO2 emissions.

Contribution

It provides the first detailed analysis of rapid color variation and dust composition heterogeneity in Comet Catalina using optical and infrared observations.

Findings

Color slope varies significantly over two days.

Comet classified as dust-rich with no significant CO/CO2 emissions.

Comet's dust coma is chemically heterogeneous with at least two components.

Abstract

We report observations of color in the inner coma of Comet C/2013 UQ4 (Catalina) with the broadband B and R filters. We find significant temporal variations of the color slope, ranging from -12.67 $\pm$ 8.16 \% per 0.1~$\mu$m up to $35.09 \pm 11.7$ \% per 0.1~$\mu$m.It is significant that the comet changes color from red to blue over only a two-day period. Such dispersion cannot be characterized with an average color slope. We also observe Comet C/2013 UQ4 (Catalina) in infrared using Spitzer and find no significant CO/CO$_{2}$ gaseous species in its coma. Therefore, we classify Comet C/2013 UQ4 (Catalina) as a dust-rich comet and attribute the measured color slope to its dust. We analyze the color slope using the model of agglomerated debris particles and conclude that the C/2013 UQ4 coma was chemically heterogeneous, consisting of at least two components. The first component producing the bluest color is consistent with Mg-rich silicates. There are three different options for the second component producing the reddest color. This color is consistent with either Mg-Fe silicates, kerogen type II, or organic matter processed with a low dose of UV radiation.