[BAA Comets] Sudden changes on C/2019 Y4 (ATLAS)

[Peter Tickner]

Hello Nick

I collected imaging data on the comet on both 3rd and 4th April but I haven't the skill or knowledge on how to do the astrometry.  Is there someone who can help me on this or can I send my raw data to you?  Last night I collected about two hours' worth of data both through a 130mm triplet APO and my 14inch SCT.  (120second subs on the 130mm and 45second subs on the 14inch).

Regards,

Peter  

-----Original Message-----
From: Comets-disc [mailto:comets-disc-bounces at lists.britastro.org] On Behalf Of Nick James
Sent: 05 April 2020 22:33
To: BAA Comets discussion list
Subject: [BAA Comets] Sudden changes on C/2019 Y4 (ATLAS)

Recent astrometry shows significant residuals in RA indicating a fairly large non-gravitational force (NGF) acting on the comet nucleus. The attached plot shows the RA residuals using an orbit solution which uses observations up to March 25. These fit weel without any NGFs. The NGFs seem to start after this date. My astrometry from tonight shows that nuclear magnitude of the comet is around a magnitude fainter than on March 25 and that the PSF is a lot broader.

The sudden onset of significant NGFs may indicate that the nucleus is very small and is in the process of breaking up or it may simply indicate a significant release of material from an otherwise intact nucleus on or around March 27. Only observations will confirm this.

Astrometry can be performed during strong Moonlight so please observe this comet as much as you can and send me any astrometry that you obtain.

Nick James.