52nd Lunar and Planetary Science Conference 2021 (LPI Contrib. No. 2548) 1107.pdf

PHOTOMETRIC FOLLOW-UP OF THE TWO COMPONENTS OF 2018 F4 PANSTARRS AFTER BREAKUP. J.M. Trigo-Rodríguez1, A. Sánchez2, and P. Manteca3. 1Institute of Space Sciences (IEEC- CSIC), Campus UAB, Carrer de Can Magrans s/n, 08193 Cerdanyola del Vallés (Barcelona), Catalonia, Spain. tri- [email protected] 2Gualba Observatory (MPC 442), Barcelona, Catalonia, Spain, 3Observatori de Begues (MPC 170), Sanpere 6 casa 22, 08859 Begues, Catalonia, Spain.

Introduction: Comet 2018 F4 (PANSTARRS) has Observatory (MPC code) Instrument revealed to be a very interesting object following a Siding Spring T/17 T 0.43 f/6.8 th hyperbolic orbit. It was discovered on March 17 , Siding Spring T/31 T 0.50 f/6.8 2018 when it was located beyond the orbit of , Siding Spring T/30 T 0.50 f/6.8 at 6.4 AU from the . During the first observations Table 1. Main observatories involved in the C/2018 after its discovery the object basically exhibited an F4 photometric follow up. asteroidal appearance, without any noticeable come-

tary activity. For that reason, it was previously classi- Results and discussion: The post-perihelion pho- fied as a hyperbolic : A/2018 F4. Dynamic tometric evolution of the two nuclei of C/2018 F4 is integration of its orbit backwards in time suggests that shown in Fig. 1. We noticed subtle changes in the ac- C/2018 F4 is a recent acquisition from the Oort cloud tivity of both C/2018 F4 components, but some details that was inserted in a very unstable orbit from interstel- are remarkable. In our data the “R” magnitude of both lar space [1]. On Sept. 12.57 2020 this comet was ob- components evolves from an Earth distance of 3.7 AU served to be splitted into two nucleus by T. Prystavski on Sept. 14th until 4.7 AU in Dec. 24th. The heliocen- [2], so we decided to perform a follow-up to better tric distance also increases in the observational interval understand the process. It is likely that the object dis- from 4.3 to 4.9 AU. This increasing distance to Earth rupted much before, perhaps during its perihelion ap- and the Sun produces a loss of magnitude noticeable as proach [2-3]. Obviously this fragmentation informs us an overall negative slope (Fig. 1). Interestingly, both that the nucleus of C/2018 F4 also exhibited a bi-lobed nuclei experienced fluctuations in its brightness, with- shape characteristic of primordial cometary bodies like out significant magnitude increases. Such alternance in 67P/Churyumov-Gerasimenko [4]. A careful study of the two cometary components magnitudes seems to the two components can provide clues on the nature of indicate that some effect of shielding could play these objects. For all these reasons we considered this a role to explain the observed photometric pattern. breakup as an opportunity to follow the evolution of a Obviously, the similar magnitude of the nuclei also double nucleus, and the possible consequences of the indicate that both components might be similar in size. mutual interactions for comet photometry.

Conclusions: We have completed a three months Technical procedure: Given that C/2018 F4 was photometric monitoring of the two nuclei of fragment- in the southern hemisphere when the comet disruption ed C/2018 F4. The two components were distancing was confirmed, we decided to perform a continuous from the Earth and the Sun and decreasing their re- follow-up of the splitted comet using several tele- spective magnitude in a similar way. We also noticed scopes located at the Q62 iTelescope Observatory, that the two nuclei experienced brigthness fluctuations Siding Spring (Table 1). From the images we followed of about 0.1 magnitudes, alternating the dominance in the evolution of the double nucleus, and studied care- brightness. Along the observational period the A com- fully the surrounding coma to watch for additional ponent was sometimes brighter than the B one, and disruptions or even outbursts. We decided to obtain then the situation alternated. We think that such fluctu- unfiltered images with a resolution of about 1 ations could be consequence of coma self-shielding arcsec/pixel or slightly better. To notice small changes each time that one of the cores places behind the coma in the release of dust from both nuclei, we also per- of the other. On the other hand, the similar magnitude formed a 10-arcsec aperture photometry that allowed observed for the two nuclei points towards a similar us to get a R-like (“R”) magnitude evolution during the size of both components. No clear magnitude increase outbound orbit. We used the USNO 2.0 catalog to get associated with specific outbursts were noticed within star magnitudes so an accuracy of about 0.1 magni- the resolution of the medium-sized instruments used. tudes is reasonable. We tried to get our photometric

monitoring as accurate as in 29P/Schwassmann- References: [1] de la Fuente Marcos, C. et al. Wachmann 1 monitoring papers, but this time the im- (2019) Res. Notes AAS 3 143. [2] CBET (2020) Cen- ages were unfiltered and the stellar fields were not tral Bureau for Astronomical Telegrams, electronic calibrated due to the observing time limitations [5-6]. 52nd Lunar and Planetary Science Conference 2021 (LPI Contrib. No. 2548) 1107.pdf

telegram 4852. [3] MPEC (2020) Minor Planet Elec- 485, 599-606. [6] Trigo-Rodríguez J.M. et al. (2010) tronic Circular 2020-S77. [4] Nesvorný D. et al. (2018) Outburst activity in : II. A multiband photomet- Astron. J. 155, 246 (10 pp.). [5] Trigo-Rodríguez J.M. ric monitoring of comet 29P/SW1. Mon. Not. Roy. et al. (2009) Outburst activity in comets: I. Continuous Ast. Soc. 409, 1682-1690. monitoring of comet 29P/SW1. Astron. & Astroph.

Figure 1. Photometry of C/2018 F4 during the last trimester of 2020

Figure 2. Consecutive images of the change in the appearance of the two components of comet C/2018 F4 after its fragmentation. One arcmin scale is identical for all images taken on: a) Oct. 13, b) Nov. 5, c) Nov. 16, and d) Dec. 9, 2020.