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From: atel@astronomerstelegram.org
Subject: ATel  17929
Message-Id: <20260729070257.B099F288052D@server.astronomerstelegram.org>
Date: Wed, 29 Jul 2026 03:02:57 -0400 (EDT)

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Posted: Within the last 24 hours
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ATEL #17929							     ATEL #17929

Title:	Is Comet C/2023 R1 (PanStarrs) undergoing a full fragmentation
		process?
Author:	Federico Manzini (Stazione Astronomica di Sozzago, Italy),
		 Mohamed  F. Aboushelib (National Research Institute of Astronomy
		and Geophysics, Cairo-Egypt),  A. Eid Abdelaziz (National Research
		Institute of Astronomy and Geophysics, Cairo-Egypt),  Virginio Oldani
		(Stazione Astronomica di Sozzago, Italy),  Costantino Sigismondi (ICRANet
		Pescara and UPRA Roma, Italy),  Andrea Brucato (Sapienza University
		of Rome, Italy),  Luigi R. Bedin (OAPd-INAF, Italy),  Alessandra Mura
		(UniPD, INAF, Italy),  Andrea Farina (UniPD, Italy),  Paolo Ochner
		(INAF, UniPD, Italy)
Queries:	manzini.ff@aruba.it
Posted:	28 Jul 2026; 21:58 UT
Subjects:Optical, Comet, Transient

The timeline of the discovery of the possible fragmentation of the Comet
C/2023 R1 (PanStarrs) is well  
described in ATEL#17915. 
Possible further clues of fragmentation can be seen in the images published
by J.F. Soulier and J.G. Bosch (https://lesia.obspm.fr/comets/lib/all-obs-table.php?
Code=CK23R010&y1=1908&m1=01 ).

Public images from the LCO Science Archive (https://archive.lco.global/
), obtained with the 2-m LCO OGG telescope (proposal TS02026A-020; authors
listed in ATEL#17915), clearly show two condensations  
adjacent to the nucleus in the images from 15 and 18 July 2026.

We also dedicated a full observing session to this Comet with the 1.88
m Kottamia reflecting telescope (NRIAG, Egypt, located in the desert East
of Cairo) on the night of 19 July.  
We measured the positions of the two condensations, designated bodies B
and C in the accompanying file 
https://web.oapd.inaf.it/bedin/files/PAPERs_eMATERIALs/ATel/C2023R1/Comet2023R1captions.pdf
and we calculated their distances from the main nucleus in arcsec projected
on the sky plane (Figure 4).

The measurements errors are estimated at +/- 0.133 arcsec for the LCO images,
and +/- 0.237 arcsec for the Kottamia image.  
The measured distances were converted into kilometers, corrected for the
distance from Earth and for  
the velocity vector angle (assuming that all fragments follow the main
nucleus on the same orbit, see Figure 5).

The corresponding positional measurements are included in the dedicated
directory  
(https://web.oapd.inaf.it/bedin/files/PAPERs_eMATERIALs/ATel/C2023R1/ ).

Over these days, body C clearly faded, while body B appeared to increase
in apparent size. This behavior suggests that the features are dust clouds
composed of multiple clumps moving away from the nucleus. 
The distances measured show a slight increase of the separation velocity
of bodies B and C from the main nucleus. The acceleration of bodies B and
C, emerging from the data, may be due to the solar radiation pressure.

A careful inspection of the LCO images revealed an additional weak condensation
very close to the  
nucleus and moving away from it (Figure 2). This body D is visible only
as a very faint trace in the images obtained at the Kottamia observatory
(Figure 3). Precise astrometric measurements could not be  
performed because this additional fragment lacks sufficient condensation.

The undergoing fragmentation is occurring with the Comet more than 3.5
AU from the Sun, and almost  
three months after perihelion.

Dossier C2023R1 fragmentation: Calibration details, figures and captions:
https://web.oapd.inaf.it/bedin/files/PAPERs_eMATERIALs/ATel/C2023R1/
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