Dust, gas activity and morphology of comet 12P/Pons-Brooks at heliocentric distances beyond 1.1 au

TL;DR

This study analyzes the dust and gas activity of comet 12P/Pons-Brooks beyond 1.1 au, revealing multiple outbursts and variations in dust and gas production as it approaches the Sun, based on extensive photometric and spectral observations.

Contribution

It provides new observational data on comet 12P/Pons-Brooks' activity at heliocentric distances beyond 1.1 au, including detection of outbursts and gas emission features.

Findings

Multiple brightness and dust activity outbursts observed.

Strong gas emissions from CN, C2, and C3 detected.

Dust activity increases significantly near the Sun.

Abstract

Comet 12P/Pons-Brooks is a periodic comet with an orbital period of approximately 71 years. Because of the period duration, aphelion of 35.3 au, and highly inclined orbit (74.2 deg), it is classified as a Halley-type comet. In this work, we present the results of the analysis of photometric and spectral observations of comet 12P/Pons-Brooks while it was at a heliocentric distance beyond 1.1 au, before perihelion passage. Quasisynchronous observations were carried out from July 2023 to March 2024 using 0.61-m and 1.3-m telescopes at the Skalnat\'{e} Pleso Observatory, 1-m telescope Zeiss-1000 Sanglokh International Astronomical Observatory, and 0.7-m telescope AZT8 at the observation station of Taras Shevchenko National University of Kyiv. Photometric observations were conducted using B, V, and R filters of the Johnson-Cousins and Bessel photometric systems. We completed our data collection with broadband photometric and spectral observations on the 2-m HCT telescope at the Indian Astronomical Observatory. During this period, the dust coma morphology and photometric data measured in the R filter, such as the apparent, absolute magnitudes and dust activity level, indicate several repeated outbursts in brightness and dust activity occurred around July 22, September 25, October 17-23, and a significant outburst was recorded on November 1-7. We detected strong gas emission features in the cometary spectrum belonging to CN, C2, and C3 molecules. Furthermore, gas production rates of these molecules were estimated using Haser's model. A comparison of dust activity level and CN gas production rate shows that dust activity increased significantly as the comet approached the Sun, while gas activity exhibited more moderate changes.