Astrometric and Photometric Monitoring of Comet 240P and its fragment 240P-B
Left: Comet 240P and its fragment 240P-B, imaged (20x DIT=60s) on 11 December 2025, with the STK in the R-band. The direction to the Sun and that of the heliocentric velocity of the comet are shown as a yellow and a blue arrow, respectively. The projected separation between the comet and its fragment was 99598 ± 324 km, with the fragment located southwest of 240P at a position angle of 234.0 ± 0.1°.
Right: The absolute R-band brightness of comet 240P (blue dots) and its fragment (red dots) during our observation campaign, derived under the assumption that only sunlight is reflected. The time of perihelion passage is indicated with a blue arrow. As previously reported, the R-band brightness of the fragment increased significantly between 30 October and 3 December 2025. Afterwards, between 3 December 2025, and 21 January 2026, the absolute magnitude of 240P-B decreased by 1.35 ± 0.14 mag, while the absolute brightness of comet 240P only dimmed by 0.87 ± 0.14 mag.
Left: The angular separation of the fragment 240P-B from comet 240P throughout our monitoring campaign.
Middle: The derived projected separation of fragment 240P-B from comet 240P during our observation campaign.
Right: The position angle of fragment 240P-B relative to comet 240P over the course of our monitoring campaign.
M. Mugrauer 2026 - All imaging data are available upon request.