Dust properties of сomet C/2012 S1 (ISON) at pre-perihelion

Comets retain relatively unprocessed material from the early Solar System, making their dust component a key probe of primordial conditions and evolutionary processes. In this context, particular interest is associated with comets that approach very small heliocentric distances, such as C/2012 S1 (ISON), since intense solar radiation and thermal processing can significantly modify their dust and gas properties, providing a unique opportunity to study the response of primitive material under extreme conditions. Observations of cometary comae using photometry, spectroscopy, image polarimetry and spectropolarimetry provide complementary constraints on the physical properties, composition, and size distribution of dust particles. The dynamically new comet C/2012 S1 (ISON) entered the inner Solar system on a near-parabolic orbit from the Oort Cloud and was considered a representative of pristine protoplanetary material. As the comet disintegrated during its perihelion passage [1], its pre-perihelion observations are of particular importance, especially given the scarcity of polarimetric and spectropolarimetric data. In this study, we present photometric, imaging polarimetric (both linear and circular), and spectropolarimetric observations obtained with the 6-m BTA telescope at heliocentric distances and phase angle from r = 4.811 and α = 7.3° to 0.76 au and α = 66.78°, respectively. The analysis focuses on dust activity level (Afρ), searching for emission at large heliocentric distances, spatial variations in linear and circular polarization. The long-slit spectroscopy at 4.81 au revealed no detectable gas emission features, indicating a dust-dominated coma at large heliocentric distance. The Afρ parameter decreases from approximately 1000 cm to 300 cm during observations. Using our photometric and polarimetric observations of this comet, we attempted to model the physical characteristics of its dust environment.

 

Acknowledgements

The research of Leonid Shakun and Oleksandra Ivanova is supported by the Slovak Research and Development Agency under Contract No. APVV-24-0076 and the grant of Slovak Academy of Sciences (grant Vega No. 2/0067/26); Oleksandra Ivanova and Johannes Markkanen are supported by grants for projects under the Mobility Program DAAD-SAS.

 

References

1. Keane, J. V., Milam, S. N., Coulson, I. M., Kleyna, J. T., Sekanina, Z., Kracht, R., ... & Charnley, S. B. The Astrophysical Journal 2016, 831, 207.