Colour variations of Comet C/2013 UQ4 (Catalina)

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 ± 8.16% per 0.1 m up to 35.09 ± 11.70% per 0.1 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.

Rapid variations of dust colour in comet 41P/Tuttle–Giacobini–Kresák

“…In particular, on 9 epochs, the comet was detected with confidence to be red, on 1 epoch its colour was unambiguously blue; whereas, on 7 other epochs the colour appeared to be neutral within the error bars. Such dispersion of the colour slope in comet 41P/T-G-K supports the conclusion previously drawn by Ivanova et al (2017) that a sole observation hardly characterizes the colour of a comet.…”

“…In this paper we present results of our recent photometric survey of comet 41P/Tuttle-Giacobini-Kresák (hereafter 41P/T-G-K) over a three-month period in the first half of 2017. As it is shown in the next sections, photometric colour of dust in this shortperiod comet underwent dramatic short-term variations, very much resembling what was found in the long-period comet C/2013 UQ4 (Catalina) by Ivanova et al (2017).…”

“…Note, rapid variations of colour were previously found, for instance, in comet 17P/Holmes (Zubko et al 2011), which was clearly related to its dramatic outburst activity at the end of October, 2007; whereas, comet C/2013 UQ4 (Catalina) did not reveal such activity during its observations. The findings by Ivanova et al (2017) raise a legitimate question as to whether comet C/2013 UQ4 (Catalina) was an exceptional case in terms of fast and dramatic temporal variations of colour in its dust. In this paper we present results of our recent photometric survey of comet 41P/Tuttle-Giacobini-Kresák (hereafter 41P/T-G-K) over a three-month period in the first half of 2017.…”

“…While the colour detected in a given comet was long considered to be a persistent feature of its dust (e.g., Jewitt & Meech 1986), it was later demonstrated that the colour can change over a considerable time period (e.g., Weiler et al 2003;Li et al 2014) and it is a function of the phase angle  (Zubko et al 2014). Furthermore, Ivanova et al (2017) have recently reported on outstanding variations of the photometric colour in comet C/2013 UQ4 (Catalina), whose dust turned from red to blue colour over only a two-day period.…”

“…We followed the reduction procedure (bias subtraction, dark and flat field corrections, and cleaning cosmic-ray tracks) in the standard manner, using the IDL routines (e.g., Ivanova et al 2016Ivanova et al , 2017Picazzio et al 2019). The morning sky was exposed to provide a flat-field correction for the non-uniform sensitivity of the CCD chip.…”