Hiroki Akisawa | Search arXiv

arXiv2026

The July 2023 Outburst of Comet 12P/Pons-Brooks: Observations and Modeling of Dust Coma and Arc Structure

We conducted continuous imaging observations of comet 12P/Pons-Brooks, which has experienced multiple outbursts since 2023 July. Among these, we determined the dust coma expansion velocities and the occurrence times for three outbursts. The outburst on 2023 July 20.39$\pm$0.05 had an expansion velocity of 207.5$\pm$0.1 m s$^{-1}$. The outburst on 2023 November 14.52$\pm$0.10 had an expansion velocity of 305.8$\pm$13.7 m s$^{-1}$, and the outburst on April 2.23$\pm$0.06, 2024 had an expansion velocity of 408.9$\pm$14.3 m s$^{-1}$. During the July outburst, in addition to the isotropically expanding dust coma, a semicircular structure (arc structure) was observed. This structure expanded without changing shape over two months, until mid-September, at a slower velocity of 52.0$\pm$1.7 m s$^{-1}$ compared to the outer coma. We hypothesize that this arc structure consists of dust ejected over a certain period during the outburst from an active region at mid-latitudes on the comet's nucleus, with a rotation axis near the line of sight. We performed model calculations to reproduce the structure. As a result, we found that the observations were well reproduced by assuming a rotation axis direction of RA = $85^\circ$, Dec = $-30^\circ$ to $-35^\circ$ and an active region latitude of $70^\circ$ during the July outburst. The active period of the outburst was shorter than the rotation period, approximately 0.7 times the rotation period. Since the dust particles comprising the arc structure escaped dissipation due to solar radiation pressure, we infer that they are dust with a ratio of radiation pressure to gravity of $β\sim 0.1$, which corresponds to a dust particle size of about $10\,μ\mathrm{m}$.

astro-ph.EP↗

arXiv2013

17P/Holmes: Contrast in activity between before and after the 2007 outburst

A Jupiter-family comet, 17P/Holmes, underwent outbursts in 1892 and 2007. In particular, the 2007 outburst is known as the greatest outburst over the past century. However, little is known about the activity before the outburst because it was unpredicted. In addition, the time evolution of the nuclear physical status has not been systematically studied. Here we study the activity of 17P/Holmes before and after the 2007 outburst through optical and mid-infrared observations. We found that the nucleus highly depleted its near-surface icy component before but became activated after the 2007 outburst. Assuming a conventional 1-um-sized grain model, we derived a surface fractional active area of 0.58% +- 0.14% before the outburst whereas it was enlarged by a factor of ~50 after the 2007 outburst. We also found that large (>=1 mm) particles could be dominant in the dust tail observed around aphelion. Based on the size of the particles, the dust production rate was >=170 kg/s at the heliocentric distance rh = 4.1 AU, suggesting that the nucleus still held active status around the aphelion passage. The nucleus color was similar to that of the dust particles and average for a Jupiter-family comet but different from most Kuiper Belt objects, implying that the color may be inherent to icy bodies in the solar system. On the basis of these results, we concluded that more than 76 m surface materials were blown off by the 2007 outburst.

astro-ph.EP↗