Richard,

I think that your image fairly conclusively shows that this has become
an ex-comet! Your analysis is interesting although separation at 100 m/s
would imply a very violent fragmentation.

Astrometric residuals are attached for the observations that I have
access to. I'm not sure they tell us much at this stage. These are all
nominally for component B. No NGFs have been included and the orbit has
a mean residual of 0".47 using observations from April 9 (when fragment
B was first measurable) to May 9 (shortly after the outburst that
probably destroyed it). Measurements after that date have not been
included in the orbit solution and the centroids are probably biased in
any case.

If anyone would like to submit astrometry of component B which is not in
this list please do so and I'll run the solution again.

Nick.

On 19/05/2020 15:36, Richard Miles - rmiles.btee at btinternet.com (via
baa-comet list) wrote:
> 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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