Maik,

Thank you for pointing us to your 2011 ICQ paper on 12P/Pons-Brooks, which shows that 12P is a long-lived comet with sightings back to at least the Year 245.

The outburst behaviour of this comet is especially interesting as it is one of approx. 20 periodic comets that belong to the 'non-fragmenting' category and which exhibit outbursts of >2 magnitudes amplitude. Indeed, it is one of about 10 periodic comets that have outburst by 5 magnitudes or more during the past two centuries, 1P/Halley being the earliest example in 1836. The most active object in this category is of course 29P/Schwassmann-Wachmann.

As to the relative position along their orbit that such intense outbursts take place, these are not really correlated with their dates of perihelion and can take place both pre-perihelion and post-perihelion. 1P/Halley is a good example of post-perihelion outbursts at true anomalies of +102° and +162°. As to 12P, which has a 71-yr period, it exhibited a post-perihelion outburst that was discovered on 1954 July 01 at +63° true anomaly, i.e. 39 days after perihelion. Here are some relevant data for 12P

Discovery Date     Amplitude (mag)     True Anomaly       Heliocentric Distance (au)     Perihelion Date       Perihelion Distance (au)
1883 Sep 23                   5                              -108°                            2.17                                 1884 Jan 26                   0.776
1954 Jul 01                     5                               +63°                            1.06                                 1954 May 23                 0.774
2023 Jul 20                     5                              -130°                            3.89                                 2024 Apr 21                  0.781

A useful working hypothesis that I have put forward in a 2016 paper is that ’non-fragmenting’ periodic comets which exhibit strong outbursts are candidates for slowly-rotating nuclei, i.e. having rotational periods >120 hours.
See:
https://www.sciencedirect.com/science/article/abs/pii/S0019103516000348

N.B. Of all the numbered comets and unnumbered JFCs, there are about 3% that exhibit these 'non-self-destructive' strong outbursts.
This low percentage is comparable to the approx. 5% of asteroids that have rotation periods of >120 hours.

Richard Miles
BAA

-----Original Message-----
From: comets-ml@groups.io <comets-ml@groups.io> On Behalf Of Maik Meyer
Sent: Friday, July 21, 2023 5:52 AM
To: comets-ml@groups.io
Subject: Re: [comets-ml] 12P/Pons-Brooks in outburst!

All,

> Confirmation of a big outburst mag 11.6 of 12P/Pons-Brooks discovered
> this evening by Elek Tamás , Harsona Observatory, Nyiregyhaza - Hungary.
> Last night 2023-07-19.8 it was mag 16.6.

this is something that was observed at previous pre-perihelion legs of 12P already in the past. I would expect additional outbursts until perihelion but with smaller amplitude. Interestingly, they do not seem to happen post-perihelion.

Another point worth mentioning is that the pre-perihelion lightcurve and the post-perihelion lightcurve show a clear asymmetry when analysing the qwell-observed last apparition. Whether this is real or an observer effect, since Albert Jones was more or less the only observer post-perihelion, remains to be seen.

For the lightcurve see p. 124 at http://www.icq.eps.harvard.edu/160J15.pdf (the paper with the ID with the 1385 and 1457 comets).

Regards

Maik