Comet 12P/Pons-Brooks, a second outburst?
ATel #16202; Federico Manzini; Virginio Oldani (Stazione Astronomica di Sozzago, Italy); Paolo Ochner (Padova University, Italy); Luigi R. Bedin (INAF-OAPd, National Institute of Astrophysics - Padova Astronomical Observatory, Italy); Andrea Reguitti (INAF-OAB, Brera Astronomical Observatory, Italy)
on 23 Aug 2023; 15:46 UT
Credential Certification: Andrea Reguitti (andreareguitti@gmail.com)
Referred to by ATel #: 16229
Following our first report of the coma expansion rate after the outburst occurred on comet 12P/Pons-Brooks
last July 19, 2023 (Manzini et al., ATel #16194), a deeper analysis of the same images revealed a second,
much brighter wavefront in the inner coma of the comet, clearly visible in the animation available at the link
below.
We measured the diameter of this inner coma on seven CCD images, publicly available, taken between July 22
and July 31, 2023, by the 2-m Faulkes North Telescope at the LCO-Haleakala Observatory (Maui, Hawaii, USA),
as done previously for the first, larger coma, but applying a different procedure. The images were first
processed with a Larson-Sekanina radial shift of 10 pixels, followed by a Larson-Sekanina rotational gradient
of 20 deg, to enhance curvilinear and radial morphological details. Then we applied a polar transformation
from the X, Y format into a rho, theta format, centered at the optocenter of the comet, assumed as the position
of the nucleus. Photometric profiles were sampled radially from the optocenter at a fixed PA of 150 deg, to
measure the exact distance in pixels of the peak intensity of the outer edge of the coma, then the
measurements were plotted after conversion into km (Fig. 1).
The linear regression analysis (Fig. 2) showed a much slower expansion rate of the coma vs the first
outburst, at 86+-18 m/s, suggesting either the presence of larger ice-dust particles with lower speed and
greater light scattering properties, or the occurrence of a second outburst, probably more collimated and
directed towards the Earth.
Calculation of the intercept of the regression line of Fig. 2 with the x axis supports the second hypothesis,
since the start of the expansion of this coma (i.e., the beginning of a second outburst) was estimated to
have occurred about 30 h after the first outburst of July 19, on JD 2460146.33+-0.5 (July 20.83, 2023+-0.5d).
We are grateful to the LCO-Haleakala Observatory for making the images of comet 12P publicly available,
thus making this study possible.
Figures and extra material are available at:
Figures and animations
