Color-indices of 1758 stars in five Kapteyn's areas in Galactic Plane / Король - индексы 1758 звёзд в пяти площадках Kapteyn, расположенных в галактической плоскости

Kharadze, E.K. and ხარაძე, ე.კ. and Харадзе, Е.К. (1942) Color-indices of 1758 stars in five Kapteyn's areas in Galactic Plane / Король - индексы 1758 звёзд в пяти площадках Kapteyn, расположенных в галактической плоскости. აბასთუმნის ასტროფიზიკური ობსერვატორიის ბიულეტენი / Bulletin of the Abastumani Astrophysical Observatory (6). pp. 17-55.

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Abstract

The importance to investigate the problem of interstellar light absorption from the point of view of contemporary stellar astronomy and particularly for making clearer our idea of a shape and extent of the Galaxy is recognized by everybody at the present time. This circumstance explains the fact that now the efforts of a number of observatories and individual astronomers are directed to manyfold investigation of cosmic absorption. Coming to the investigation of the problem from different points of view, the astronomers apply for this purpose different methods, apparatus and means. The task of the investigation of selective light absorption in different directions is closely connected with the problem of cosmic absorption. The ground for the investigation of selective absorption is simple. As it is known, if the particles of cosmic dust producing the scattering of light have less than joint diameter, the absorption depends upon wave-length, being greater for the rays of shorter wave-length. Therefore the stars which are beyond the mass of similar particles will seem to the observer redder than they are in reality. In connection with this the color-indices of the stars seen through such medium will be greater than it corresponds to their spectral types. The excess of the color-index observed in regard to normal one, that is color-excess will be the greater, the more intensive absorption, or the longer the distance passing by a ray of light in the scattering medium. Therefore for the estimation of the selective absorption it is necessary to determine the color-indices and compare the values observed to those which correspond to their spectral types, determined according to the intensities of spectral lines, that is on the ground of spectral classification. If, in addition to this, the objects for which color-excesses predetermined will be distributed in different directions of the sky, then it is not difficult to come to the conclusion about the shape, extent and properties of absorbing medium existing in the Galaxy. The next Table IX contains the comparison of out values of photographic magnitudes with those obtained at 1) Groningcn (BSD). The last two lines of this Table contain the algebraic and the arithmetical means for the differences Mt Kanobili BSD, Mt Kanobili-Mt Wilson, etc. As we see the systematic errors for all these differences exept Mt Kanobili Harvard, are insignificant. Great interest represents the analysis of the average values of the color-indices of stars of a given spectral class and a given stellar magnitude. A number of stars taken in each plate enables us to deduce these average values with rather great reliability. To our mind the data of last five Tables can serve is a sing of the fact that in the corresponding areas of the sky there is noticeable reddening of stars called forth by the presence of absorbing medium. This reddening is confirmed by the increase of the mean color-index of a given spectral group from brighter stars from statistically near) to fainter stars. It is naturally, of course, lo put a question about the possibility of a systematic error in our determinations of color-indices that can. in its turn, arouse doubts, about the color-excesses and about the possibility of interpretation of mean color-indices from absorption point of view. For this case we can remind the fact that we can determine color-indices for many areas distributed in different galactic latitudes and that the possibility of comparative, differential examination of them excludes the above mentioned danger. From this point of view it is interesting to give the comparison with some data here which we have obtained on the ground of preliminary reduction of some KSA located in different galactic latitudes. The data of last Table though based on incomplete reduction of KSA 5 and KSA 14, still is rather convincing. They point out to the absence of a color-excess in the directions far from the galactic equator. It is interesting that in the given case it was not discovered either the increase of the mean color-index with the decrease of brightness of stars that is clearly observed for the directions which probably pass through absorbing medium (KSA 24, 40). The data given in the present work cannot serve for a detailed analysis of color-excesses which they undoubtedly reveal. Such analysis will be possible only after the determinations of the color-indices of stars in other KSA, situated both near the galactic plane and in different distances from it, have been finished. Besides that time we shall have more reliable system of normal color-indices. But the material represented here gives the foundation to think that the data of our work which is being carried on will be used with accuracy for future investigation of galactic absorption in different directions. November, 1941.

Item Type: Article
Subjects: Q Science > QB Astronomy
Divisions: Institutes > Evgeny Kharadze Abastumani National Astrophysical Observatory
Depositing User: თამარ ჭაღიაშვილი
Date Deposited: 16 Jul 2018 10:11
Last Modified: 16 Jul 2018 10:11
URI: http://eprints.iliauni.edu.ge/id/eprint/8236

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