Hopefully the attached demonstrates that the comet has now disintegrated.

Some thin cloud was around last night and it never turned into a properly
clear night but as the target was circumpolar at the time I was still able
to follow it for a couple of hours as it tracked along my northern horizon
some 26 degrees from the Sun.

We can now see the result of the outburst on May 8. Although Component B,
the most massive part of the comet, appeared to have survived that outburst,
this was an illusion as we now know it disintegrated and although we could
see a bright pseudonucleus at that location on May 9-16, we were just
witnessing the expanding debris cloud. Of much more interest is what
happened to the solid body of B. It appears that there was an explosive
event on May 8 that blew a considerable mass of material sunwards at speeds
of 80-100 m/s.

The ejected material comprised a leading body with debris trailing behind it
(see my email of May 16). The leading body disintegrated as a consequence of
this energetic event. If  we do astrometry on Component B up until it
disappeared, we may see that it was slowed slightly following the outburst -
a necessary result of conservation of momentum. So although we measure the
separation velocity to be 80-100 m/s, we need to do the astrometry to see
how the change in velocity was shared between the two 'fragments'.

Richard

----- Original Message -----
From: "Nick James" <ndj@nickdjames.com>
To: <baa-comet@simplelists.com>
Sent: Sunday, May 17, 2020 7:33 AM
Subject: [BAA Comets] C/2019 Y4 on May 16

>I think we can safely say that C/2019 Y4 will soon be redesignated
> D/2019 Y4. It faded another 0.5 magnitudes from May 15.9 to 16.9 and
> there is no photocentre left for astrometry. All that we see now is two
> fading trails of debris.
>
> It is a very challenging target now as it dives towards the northern
> horizon but please keep imaging it if you can.
>
> Nick.
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