Comet C/108P (Ciffreo) is not splitting
ATel #15177; Federico Manzini (SAS), Paolo Ochner (University of Padova; INAF-OAPd), Virginio Oldani (SAS), Luigi R. Bedin (INAF-OAPd), Andrea Reguitti (UNAB; INAF-OAPd), Jean Gabriel Bosch, Jean François Soulier
on 25 Jan 2022; 11:10 UT
Credential Certification: Andrea Reguitti (andreareguitti@gmail.com)
Comet C/108P was discovered by Jacqueline Ciffreo on November 8, 1985 with the 0.9-m
Schmidt telescope of CERGA-France (IAUC 4135 ). Its short-term orbit was calculated by D. Green
(IAUC 4137 ).
The comet was followed by our group in its current apparition since November 7, 2021, when it
showed well-defined morphological structures in the inner coma.
Following some alerts of a possible fragmentation of the nucleus ( https://groups.io/g/comets-ml ),
an observation of the comet was scheduled on December 30, 2021 with the INAF-OAPd 1.82-m Copernico telescope (Asiago Astrophysical Observatory, Italy).
On the high-resolution CCD image, the false nucleus appeared very bright, slightly elongated in PA
30°, with an average FWHM of about 1.8 arcsec (about 1,300 km at the distance of the comet).
The tail was oriented towards PA 245 deg. A bright condensation, elongated in the E-W direction, was
visible in the coma at PA 90 deg, which appeared detached from the nuclear region, with a center of
gravity about 7 arcsec east of the optocenter (about 5,250 km at the distance of the comet) (Figure
1).
A very similar morphological structure had already been observed during the comet's last orbit in
December 2014, albeit with instruments of smaller diameter and lower resolution (J.G. Bosch, A.
Maury, J.F. Soulier), in almost analogous geometric conditions to those of 2021 (Figure 2).
Similar morphology was also observed about 1 month after the discovery of the comet, by S. M.
Larson and D. Levy, who reported that CCD images obtained with 1.5-m and 0.5-m telescopes in
December 1985 showed a detached dust tail extending over 20" to the north-east of the nucleus
and curving in the direction of increasing position angle. The distance of the point of maximum
intensity in the tail was about 6" from the nucleus (IAUC 4158 , and Bull. AAS 1986, Vol. 18, p.811).
In the same IAUC A.R. Klemola (Lick Observatory) wrote that an exposure with the Crossley
reflector on 1985 Dec. 17.3 UT showed a sharp stellar object separated by an almost clear gap
from a diffuse coma or tail feature. The center of the diffuse feature was 5.6" to the northeast of the stellar object.
A more in-depth analysis, supported by a modelling of the inner coma that takes into account the
dust outflow from discrete sources on the surface of the nucleus, shows that this structure,
recurrently observed during previous apparitions of the comet, may originate from a strong activity
of an area in near-polar position on a nucleus with a spin axis directed approximately towards the
Sun (Figure 3). The dust outflow, emitted collimated in almost sunwards direction, would be pushed
back by the radiation pressure and, due to the geometry of the observation, would appear
projected onto the coma, thus creating a 'clump' effect that could resemble a detached fragment
which, however, is not real.
Figures are available at:
https://web.oapd.inaf.it/bedin/files/PAPERs_eMATERIALs/ATel/C1985P/FiguresATEL108P.PDF
Link
