Shain, P.Th. და შაინი, პ. (1943) The Study of Selective Absorption in the Region of the Rift of Milky Way in Aquila / სელექტური შთანთქმის შესწავლა "ირმის ნახტომის" განშტოებაში. აბასთუმნის ასტროფიზიკური ობსერვატორიის ბიულეტენი / Bulletin of the Abastumani Astrophysical Observatory (7). С. 189-199.
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Introduction. The region of the rift of the Milky Way near Aquila deserves special attention. First, the dark region is exceptionally large. All the known dark nebulae seem to be of very moderate size when compared with it. Perhaps, an analogy may be drawn between this region and some dark details observed sometimes in thე extragalactic nebulae. But this region is also of interest from another point of view. Namely, not long ago one believed that in addition to the separate dark nebulae there is near the middle plane of the Milky Way a layer of selectively absorbing matter continuously extending at least 011 1000—2000 parsecs. At present we have some evidences in favour of the hypothesis on discontinuous distribution of the absorbing matter on the sky as well as in space. In this case the color-excess must increase not uniformly with increasing distance and will be zero till in the given direction a cloud is encountered. Then we shall have a more or less rapid increase of C. 1£. in dependence on the optical thickness of the cloud, l or the stars behind it the color-excess will be constant till in the same line of sight is encountered a second cloud causing a new jump in the C. h. Therefore, the change in the color-excess with increasing distance or apparent magnitude will be generally of discontinuous character. But till now we have no serious observational evidences in favour of such correlation between C. L. and the distance. The change of the density of stars with the increasing distance. In order to judge about the change of the density of stars D(r) with distance it is necessary to know the coefficient of general absorption. The latter was obtained from the derived C. F., (see above). The few observational data show that the space density of B and A stars rapidly decreases with the increasing distance (see, for instance, Bok, Aph. J. 90, p. 260, 1939). It is known that the density gradient for the spectral classes B and A is higher than that for the stars in general- For our region we have a decrease of the density at the distance of 500 parsecs about 1.5—2.2 tunes for the B8 - A0 stars and 1.8- 2.5 for A2—A5 ones. The derived high value for the density gradient partly depends on the adopted value of the coefficient of general absorption. But even if we had assumed for the ratio (general absorption: C. E.) the value 6.0 instead of 4.0. the high negative density gradient could not be removed. Some systematic error in the spectral classification of faint stars may also influence the results. It seems astonishing, that no sensible difference for the function D(r) is observed in our three zones A, B and C. However, it is necessary to note that even the richest /one c K not homogeneous: it embraces a small bright cloud and partly a dark region. The number of the stars in this cloud is small and it could not be considered separately. For the reasons mentioned above the accuracy of the results with respect to the function D(r) is low but we think that the figures as given here characters to some extent the change of the density of B8-A0 and A2—A5 stars with the increasing distance. It is of interest to note that the results obtained here are similar to those found by Wok for Monoceros notwithstanding the great difference in the structure of the regions under consideration. Simeis - Abastumani October, 1942
| ობიექტის ტიპი: | სტატია |
|---|---|
| თემატიკა: | Q Science > QB Astronomy |
| ქვეგანყოფილება: | Institutes > Evgeny Kharadze Abastumani National Astrophysical Observatory |
| განმათავსებელი მომხმარებელი: | თამარ ჭაღიაშვილი |
| განთავსების თარიღი: | 25 მაისი 2018 11:05 |
| ბოლო ცვლილება: | 25 მაისი 2018 11:05 |
| URI: | http://eprints.iliauni.edu.ge/id/eprint/8003 |
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