FellowPhD Oleksandra Ivanova
Project NameInvestigation of development of the physical activity of dynamical new comets over the wide range of heliocentric distances
Host organisationAstronomical Institute
Duration of the project25.02.2016 - 31.12.2018

Abstract
The main goal of the presented project is to study the physical properties of the atmospheres and tails in the dynamically new comets. The project is focused on the study of the evolution of physical activities of the comets depending on their distance from the Sun. The archived photometric, spectrophotometric, and polarimetric data, as well as the new observations of the comets at different heliocentric distances, will be used to solve this topic. Our objects are comets with a perihelion distance, q, in the range of 0.01 - 3 AU. In the first stage of the project, the observations of the selected comets (using different methods of observations) with higher activity at the large heliocentric distances (r>4 AU) will be presented. Here, we also include observational data, obtained by principal investigator (PI) of the presented project, based on the previous observations. In the second stage of project, the observations of new comets (with broadband filters (BVR), which will be active at large heliocentric distances (r>4 AU), will continue. We want to obtain further observations of the comets (with narrow band filters), which were observed at large heliocentric distances during the first stage of the project, but this time will be in a closer distance to the Sun (r<3 AU). In the final stage of the project, an analysis of the obtained spectroscopic, photometric and polarimetric data will be done: detection of gas emission, estimation of dust and gas productivity, morphology of dust and gas coma and estimation of the degree of polarization at large phase angles. We will construct light curves of the cometary brightness changes. Also, the estimations of refractive indexes, sizes and density of particles of comet dust will be done. To do these estimations, we use the photometric and spectropolarimetric observations and results of the measurements performed in space (taken from the literature) and based on a modelling.

Project Summary with Interim Results

The main goals of the present project are to study physical properties of atmospheres and tails in dynamically new comets and to compare them with those of comets from other dynamical groups. Currently, attempts are underway to establish taxonomy of comets on the basis of their composition and to link it to the place of their origin. A comparison of physical characteristics of short-period comets with those of long-period and new comets may elucidate which properties of comets are primordial and which are a product of subsequent evolution. Physical properties of the body mainly depend on genetic factors such as stratification of temperature with distance from the Sun, structure and density on the surfaces of bodies, the ratio of volatile and refractory materials, and so on. However, the role of evolutionary processes that have determined the dynamics of small bodies, sources of internal energy, etc., can also be significant. It is recognized that the temperature gradient in the initial dust cloud and the presence of massive proto-planets influenced the processes of accumulation, formation and evolution of small bodies in the Solar System. This process results in different properties of bodies in the main asteroid belt (the difference between the properties of main types of asteroids S, C, E, etc.), objects of the Kuiper Belt, and the Oort cloud. Collisions, dynamic, and evolutionary processes have generated in the Solar System objects with transient properties - meteoroid streams, objects such as Centaurs, comets with dynamic characteristics of the main asteroid belt, comets of different classes regarding polarization, thermal properties, and dormant cometary nuclei.

The main goal of the first year of work is a comprehensive study of the observed characteristics of the radiation scattered by dust particles and gas properties of comets of different dynamical groups in the Solar System. Dust and gas are parts of atmospheres of comets, active centaurs, and also a new class of objects - comets of the main asteroid belt. Dust and gas play an important role in the process of forming different bodies and in their evolution. The main observable characteristics of scattered radiation, such as intensity, color, polarization, their spatial and spectral characteristics depend on a mechanism of scattering of light on the dust particles and physical properties of dust which are size, composition, structure, and form. So, a study of properties of radiation scattered by dust particles of different objects is the basis for the development of theoretical ideas about the interaction of radiation with matter, building physical and cosmological models of celestial bodies.

 

During reported period, complex observations and data analysis of dust properties for 16 new objects (10 distant comets with perihelion more than 4 au, 6 dynamically new comets, 1 active centaur, 1 “active” asteroid and 3 short-period comets) were made. We obtained data using different telescopes: big-sized - the 6-m SAO RAS telescope (Russia), the 4.1-m SOAR telescope (Chili), the medium-sized 2-m telescope p. Terskol (Russia), and small-sized - the 0.80-cm (Ukraine), 0.61-m Skalnate Pleso (AI of SAS), 0.60-m p. Terskol (Russia), 0.40-m Kourovka AO (Russia), 0.20-m telescopes (Belgium). We used different observational methods: photometric (using BVRI broadband filters, cometary filters), spectral (long-slit spectroscopy), and polarimetric observations of the selected objects. The data obtained in the previous observation period were processed and analyzed. The software for data processing and model analysis of the data was upgraded. We used the original methods and mathematical modeling of physical processes for interpretation of results. Based on data analysis, we estimated the optical properties of the selected comets, “active” asteroids and centaurs. We also tried to find a connection between their physical and dynamic characteristics to identify features associated with different areas of their formation in the Solar System or a different kind of evolution.

Observations and analysis of data for comet 67P / Churyumov-Gerasimenko within the program of the ground-based support of the ROSETTA cosmic mission were the most important results obtained during reported period. We obtained many physical characteristics of the comet, including an estimation of gas and dust productions, which confirmed that the comet 67P / Churyumov-Gerasimenko corresponds a class of “depleted” in carbon. We were found that cometary dust production rate is decreased in 4 times during observation period. Identified radial changes of polarization and color of cometary coma correspond the evolution properties of dust particles. Model interpretations of obtained data showed a decline in sizes of average particles with increasing of distance from the cometary nucleus. This may be caused by the disintegration of particles due to fragmentation and sublimation.



Fig.1 Linear polarization maps of comet 67P/Churyumov-Gerasimenko: there is a complex structure of the coma in polarized light with areas of high and low polarization.

 

Hence, determination of physical characteristics and optical properties of particles of various populations of small bodies in the Solar System allows one to identify similarities and differences in these characteristics depending on location and their relationship with the dynamic characteristics. The results will be used to build physical and cosmological models of the objects and will allow the fundamental problems of origin and evolution of the Solar System to be solved.