Stellar and extragalactic astronomy

Observations and Comprehensive Investigation of Stars on Different Evolutionary Stage

Project Participants: Nino Kochiashvili, Ia Kochiashvili, Sopia Beradze, Tamar Tsinamdzgvrishvili

This is the educational research project. We are comprehensively probing the stars on different stages of their evolution; this includes using available observational facilities and astronomical databases. These are the targets of our investigation:

a) EM CEp – the Main Sequence Be Star. It is widely accepted that Be stars do not undergo flares. Although in the case of EM Cep the picture looks different – few flares have been observed for this star, including powerfull and “unusual” flare that was observed in the Abastumani Observatory in 1991; the flare lasted not less than two hours. In the frame of this project, we are intensively observing the star photometrically and spectroscopically in order to reveal further possible pecularities. One of the objectives is to establish, whether the object is a binary system or a pulsating star.

b) Luminous Blue Variables and Wolf-Rayet Stars. Investigation of all types of massive stars, especially those that are on the short-lived transitional evolutionary stage, has been intensively carried out during the last decades. “On the basis of observations of massive stars we can trace the evolution of galaxies throughout the whole history of the universe”. In 1998 the accelerated expansion of the universe was established on the bases of observations of the type Ia supernovae; and in 2011 the discovery was awarded the Nobel Prize. Particular interest in studies of massive stars is seen after explosion of so called type II supernova, SN 1987A. This event proved that, indeed, the core collapse of a massive star causes a supernova explosion, but it was found that for this supernova the “ancestor” star was the blue supergiant and not the red one, as it was assumed before. Therefore, the theory of evolution of massive stars was again revised after this event. The massive stars that are on the short-lived transitional phase of evolution are of a special interest, because they are believed to have connection with the so-called “supernova impostors” and also “real” supernovae. These are the massive supergiant and hypergiant stars and the so-called Luminous Blue Variables (LBVs hereafter). Hypergiant P Cygni has the longest investigation history among all LBVs. Observations of this star has begun from 1600. As about the Abastumani Observatory, observations of P Cygni started in 1930-ies. We have unpublished photoelectric observations performed by N.Maghalashvili and E.Kharadze during 1951-1983 years. Currently, we are observing the star at the Abastumani Observatory using 48 cm reflector telescope, which is equpped with the CCD and U,B,V,R,I filters and also at the 2 m telescope of the Shamakhy Observatory in Azerbaijan. High resolution spectral data has been obtained. Observations will continue for at least 7 years. The hypothesis about the binarity of P Cygni needs to be revised. It is important to figure out the role of binarity in general evolutionary framework and also in gigantic eruptions of the LBVs. LBVs represent stars on the short-lived (approximatelly 40000 years) evolutionry stage which is apparently, followed by the WR stage. Therefore, we are also observing WR 134 in order to figure out the observational facts about evolutionary ties of these two types of stars.

c) Binary Stars. In the frame of this project we are gathering observational data and studying the binary stars. We are also carrying out observations of the Kepler space telescope targets at the Abastumani Observatory. Some other goals include working on solving the orbits of binary stars and carry out asteroseismic investigations

 

 

Research of galactic open clusters, in order to identify their binarity and multiplicity and some particular problems related to this

research supervisor: Giorgi Javakhishvili – Doctor of Astrophysics, Associate Professor – Natural Sciences and Engineering Faculty, Ilia State University, E. Kharadze Abastumani Astrophysical Observatory researcher. e-mail: javakhishvili@iliauni.edu.ge

 

The goal of research is to reveal double or multiple galactic open clusters, and their study through observational and numerical analysis methods. The topic is related to the problems of stellar and galaxy evolutions, as well as the galactic structure in general. Within our Galaxy, science knows several double open stellar clusters whose components distinctive against each other. As an examples could be named c and h Persei. However, at the same time, there should be a number of double or a multiple clusters, which overlap each other and thus are visible as a single clusters. In order to determine their binarity and multiplicity could be used distributions of cluster member stars magnitudes. When examined such distributions for galactic open clusters included in WEBDA database – majority of distributions happen to be Gaussian distributions with one peak. In the same time, in some other cases distributions have two, three or four distinguished peaks. This may be an indicator of their binarity and multiplicity, but also may reflect the characteristics of their internal structure. Such clusters are not properly understood. The goal of our project is to research mixed clusters (galactic open clusters with two and multiple distribution peaks) – in terms of proving their binarity/multiplicity, as well as study their structural characteristics. Above all mentioned, project includes study of age distributions for galactic open clusters.

 

 

 

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