Jeremy, thanks for the link to this very interesting paper.

Nick, I certainly agree with you regarding the brightness evolution of the
comet. I am attaching a plot containing measurements by myself using different
telescopes and some data of S. Fritsche (indicated by the telescope
identifier TS1006D). Those are magnitudes derived from green filtered images
using a fixed aperture diameter of 50000km. I have added two model light curves,
one derived from data until April 1st and the other from recent observations.
The similarity of both curves - despite the difference in the activity
parameter - indicates that the comet is slowly recovering and not too far from
the evolution it has shown early this year. It does not look like an
disintegrating comet at present.

Regarding the phase angle effect. It is obvious that there is a brightening
in mid-April at the time of lowest phase angle. But the brightness decrease
after that time is much larger and steeper than before. Therefore I believe
that the phase angle affect is not the major source of the brightness dip.
In addition the projection effect of changing tail orientation is also
not strong enough to account for the dip. I have measured the comet including
the tail and obtained a boost in total comet brightness of only about 0.3mag by
the end of May/beginning of July (with respect to my large aperture photometry
results as published at COBS).

Maybe the observed strange lightcurve reflects variation in the size of
the active region on the nucleus or changing geometry with respect
to the solar radiation, e.g. precession (especially if one assumes a largely
non-spherical body).

Anyway, an interesting object and only by further observations we might get
new clues about what is going on there ...

Thomas

> Am Tue, 9 Jul 2024 23:32:14 +0100
> schrieb Nick James <ndj@nickdjames.com>:
>
> Denis,
>
> Sekanina is not predicting fragmentation post-perihelion. He thinks that
> fragmentation started on March 21 and he predicts that we won't see the
> comet again once it is lost to ground-based observers in August.
>
> His evidence, amongst other things, is the rapid rise in brightness up
> to April 15 and then the following fall. I'm surprised that he doesn't
> mention the low phase angle effect around this date. He also observes
> that there is larger magnitude scatter after April 15 (he's using Andrew
> Pearce's estimates from COBS) and that this is indicative of
> fragmentation. We don't see this in our latest near-nucleus lightcurve
> (attached) which looks smooth and well-behaved. It doesn't look like the
> lightcurve of a fragmenting object to me.
>
> His arguments using the tail morphology and AFrho seem rather more
> convincing but I think more data is needed while the comet is still
> observable from the ground.
>
> Nick.
>
>
> On 09/07/2024 15:34, buczynski8166 at btinternet.com (via baa-comet
> list) wrote:
> > Hi Jeremy,
> > A distinct warning about the possible fragamentaion of C/2023A3 by the
> > leading cometary scientist.
> > I wonder could there be any similarity between this possible post
> > perihelion  fragmentation and the fragamentation of Comet  C/1975V1 West
> > which also happened post perihelion and produced a wonderful visual
> > spectacle.
> > Denis Buczynski
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