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

[Nick James]

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.
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