The optical characteristics of the dust of sungrazing comet C/2012 S1 (ISON) observed at large heliocentric distances

Abstract

Phone: +421527879126 E-Mail address: oivanova@ta3.sk Highlights• We present the results of photometric observations of comet C/2012 S1 (ISON) performed from September 29 to December 16, 2012.• We present the results of spectroscopic observations of comet C/2012 S1 (ISON) performed on February 9, 2013.• Photometric colours of the comet are redder than solar colours.• Analysis of spectral data shows the growth of the dust grain reflectivity with increasing wavelength.• Molecular emissions were not detected in the spectra of this comet.• The optical characteristics of the dust significantly depend on the chemical composition and structure. Effective medium approximations for light scattering by porous aggregates should be used for their evaluations. ABSTRACTWe present an analysis of the photometric and spectroscopic data of the comet C/2012 S1 (ISON) observed at the heliocentric distances of 6.21 -4.81 AU. The photometric observations were made with the 60-cm Zeiss-600 telescope (ICAMER, peak Terskol, Russia) and the spectroscopic observations were performed using the SCORPIO-2 focal reducer mounted in the prime focus of the 6-m BTA telescope (SAO RAS, Russia). We analyse the B, V and R-band images to describe the dusty cometary coma and to investigate its brightness, colours and dust production rate. The spectra cover the wavelength range of 3600-7070 Å. No emissions which are expected in this wavelength region were detected above the 3σ level. The continuum shows a reddening effect with the normalized gradient of reflectivity along dispersion of 9.3 ± 1.1% per 1000 Å. A dust-loss rate was derived using the obtained values and under the different model assumptions. Our simulations clearly indicate that to retrieve dust production from the observational Afρ parameter is an ambiguous task.The result of such a procedure is strongly dependent on dynamical (e.g. effective density and cross-section) as well as optical (e.g. scattering coefficient and phase function) characteristics of dust grains. A variation of the mentioned parameters can lead to dramatic changes in the evaluation of mass production. We demonstrate that the dynamic and optical properties are interconnected via the microscopic properties of dust grains (effective size and porosity).

Photometry, spectroscopy, and polarimetry of distant comet C/2014 A4 (SONEAR)

“…We did not calculate the dust mass production rate in this comet because, as showed in Ivanova et al (2018), the result of such calculations strongly depends on the physical characteristics of the dust. Variations of the mentioned characteristics can lead to dramatic changes in the evaluation of the dust mass production.…”

Small Bodies of the Solar System Active at Large Heliocentric Distances: Studies with the 6-Meter Telescope of Sao Ras

“…However, most of the questions remain unresolved, and we can only introduce a given parameter as an estimate. As we showed in our paper Ivanova et al [45], an accurate estimation of dust productivity from the Afρ parameter is an ambiguous task. The result of such a procedure depends strongly on the dynamic (e.g., effective density and cross section) and also optical (e.g., the scattering coefficient and phase function) characteristics of the dust particles.…”

“…In 2006, the 6-m SAO RAS telescope started a comprehensive program aimed at investigating the activity of distant comets, including a search for gas emissions responsible for the formation of comets and the tails of these comets. Long-slit spectra were obtained for more [42,43,45]. than 30 distant comets over the course of ten years.…”

“…Particular attention was also devoted to the task of comparing the changes in the dust properties of dynamically new comets with a perihelion less than 0.5 au. Such a detailed investigation of the activity evolution was carried out for the comet C/2012 S1 (ISON), the perihelion of which was 0.012 au; it was active at distances greater than 9 au from the Sun [40,45,55,63,106].…”

“…Despite the uncertainty of the optical properties of dust particles [45], we can compute some dust characteristics. For example, the color analysis (estimate of the spectral reflective ability) often used in photometric observations shows (especially in aperture photometry) that the light scattered by dust particles in the coma is in most cases redder than the incident solar radiation.…”