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

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 Skalnaté 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.

Figures (10)

• Figure 1: Intensity maps of comet 12P/Pons-Brooks in the R filter on July 30, October 10, and November 19, 2023. Panels (a), (d), and (g): Direct images of the comet. Panels (b), (e), and (h): Images processed by the rotational gradient method 1984AJ.....89..571L. Panels (c), (f), and (i): Images to which a division by the $1/\rho$ profile has been applied 2014Icar..239..168S. The colour scale does not accurately reflect the comet's absolute brightness. The arrows point toward the Sun, the north, the east, and the negative velocity vector of the comet as seen on the plane of the sky.
• Figure 2: Co-added images of comet 12P/Pons-Brooks in the R filter to which a rotational gradient technique of 1984AJ.....89..571L is applied on March 10, 2024.
• Figure 3: Schematic diagram of the formation of an active structure in the form of two "horns" for comet 12P/Pons-Brooks: panel (a) shows the existence of a jet structure with a cone-like geometry, and panel (b) schematically illustrates the corresponding brightness distribution of such a feature as seen by an observer.
• Figure 4: Application of a geometric model to interpret the structure of jet features (a -- for July 30, 2023, b -- for October 10, 2023, c -- for November 19, 2023, d -- for March 10, 2024). Active structures that come from different regions are shown in different colours.
• Figure 5: The distribution of the apparent magnitudes in B, V, and R bands of comet 12P/Pons-Brooks throughout the entire observation period. The figure shows changes in magnitude over time and with heliocentric distance. Vertical dashed lines indicate dates of outbursts taken from the literature (see Section 3.1 for more details).