Problem of Diffuse Nebulae and Cosmic Absorption / დიფუზიურ ნისლოვანედთა და კოსმიური შთანთქმის პრობლემა

Ambarzumian, V.A. and ამბარცუმიანი, ვ. and Gordeladse, Sh.G. and გორდელაძე, შ. (1938) Problem of Diffuse Nebulae and Cosmic Absorption / დიფუზიურ ნისლოვანედთა და კოსმიური შთანთქმის პრობლემა. აბასთუმნის ასტროფიზიკური ობსერვატორიის ბიულეტენი / Bulletin of the Abastumani Astrophysical Observatory (2). pp. 37-68.

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Abstract

As known, among diffuse nebulae there are both the nebulae with continuous spectrum and those with the spectrum consisting of emission lines. It has been established that the luminosity of any diffuse nebula in every case is connected with some star of large absolute brightness, located either within the nebula or close to it. Moreover, it was observed that provided the spectrum of illuminating star is of Bi or later type, the spectrum of nebula turns out to be continuous and coincides with the spectrum of the star. In this case we deal with a simple reflection of star light by the nebula and there are all reasons to suppose that this diffuse reflection is produced by solid particles of cosmic dust. However, in the case when the star causing radiation belongs to O or Bo type, the spectrum proves to be the emission one. As it has been shown by Rosseland and Zanstra this emission is due to the excitation of atoms of gases, contained in the nebula, by the short wave radiation of star. In any case each luminous diffuse nebula is connected with some star causing this luminosity. However, the ultimate character of this connection is not yet known. Conclusion. As we have shown in the present paper the diffuse nebulae are not dynamically connected with illuminating stars and are probably accidentally met with the latter in space. This leads to the conclusion that J there exists a large multitude of non-illuminated diffuse nebulae distributed 1 haphazard in the galactic space. Computation has shown that the absorption of light of distant stars produced by these nebulae should be of the same order of magnitude as the £ observed general absorption. Therefore the cause of the general absorption can be sought for just in these non-illuminated nebulae. This assumption permits to explain large fluctuations in the general and selective absorption when u passing from one region of the sky to the neighbouring one. In addition we n have shown that from our point of view one should not expect any correlation between the surface brightness of different regions in the Milky Way ti and the selective absorption coefficient in those regions. From this standpoint the reflecting, emission as well as «dark» nebulae are individual representatives oi the homogeneous class of diffuse nebulae. Diffuse nebulae posing large optical thickness and not being illuminated by bright stars will soon “dark” ones. Diffuse nebulae illuminated by stars of Br – M types simply reflect their light and finally diffuse nebulae falling into the field of radiation of O and Bo stars give the emission spectrum being essentially of the same physical nature as the reflection nebulae. The difference between the reflection and omission nebulae is similar to the between comets located at large and small distances from the Sun. On the other hand the assumption on the presence oi a special continuously distributed absorbing medium in galaxy proves to be unnecessary. Finally the proposed point of view is the most simple one, as it embrace all the phenomena referring to nebulae with continuous, emission and mixed spectra, to dark nebulae as well as to selective and general cosmic absorption. September, 1937

Item Type: Article
Subjects: Q Science > QB Astronomy
Divisions: Institutes > Evgeny Kharadze Abastumani National Astrophysical Observatory
Depositing User: თამარ ჭაღიაშვილი
Date Deposited: 21 May 2018 10:27
Last Modified: 02 Jun 2018 18:41
URI: http://eprints.iliauni.edu.ge/id/eprint/7992

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