The ice and organics particles in distant comet C/2014 A4 (SONEAR)

Small ice-rich bodies from the outer region of the Solar System are recognized as remnants of the long-time evolution of the protoplanetary nebula. Currently, three reservoirs of the comets are mainly identified: the trans-Neptunian region, the Oort Cloud, and Asteroid belt (i.e., main-belt comets and active asteroids).

The compositional taxonomy of the small icy bodies allows establishing a possible correlation between physical properties of the distant dwellers and their orbital characteristics shedding light on the primordial physical conditions at the places of their formation. Studies of distant comets in their active phase can be especially informative.

Polarimetric, photometric and spectroscopic observations of distant comet C/2014 A4 (SONEAR) were obtained using the multi-mode focal reducer SCORPIO-2 attached to the prime focus of the 6-m telescope BTA of the Special Astronomical Observatory (SAO RAS).

We analyze the dust environment of the distant comet C/2014 A4 (SONEAR), with a perihelion distance near 4.1 au.

The comet displayed an extended coma with highly condensed material in the near-nucleus area and a long tail in the antisolar direction. The fan-like structure (J) in the sunward hemisphere was detected (Fig.1).

From spectral observation no emissions were detected in the 3800 – 7200 Å wavelength range.

The radial profiles of surface brightness differ for r-sdss and g-sdss filters, indicating predominance of submicron and micron-sized particles in cometary coma. The photometric characteristics are consistent the fragmentation of the dust particles in the coma.

Analysis of the polarization and color and their change with the distance from the nucleus showed that (1) dust particles in the distant comets are small (<1 μm) that is not surprising as there is too little gas that can lift large particles; (2) dust contains icy particles and particles composed of (or covered by) tholin or similar organics; (3) icy particles fragment as they move out of the nucleus.

Fig.1. Comet C/2014 A4 (SONEAR) in the g-sdss filter, obtained at the BTA/SCORPIO-2. (a) direct images of the comet in relative intensity; (b) relative intensity image processed using the division by the 1/ρ profile method; (c) relative intensity images to which a renormalization method was applied.

Published: Oleksandra Ivanova, Igor Luk'yanyk, Ludmilla Kolokolova, Himadri Sekhar Das, Marek Husárik, Vera Rosenbush, Viktor Afanasiev, Ján Svoreń, Nikolai Kiselev, Vadim Krushinsky (2019). Photometry, spectroscopy, and polarimetry of distant comet C/2014 A4 (SONEAR). Astronomy & Astrophysics, 626, A26.