The occurrence of carbon isotopes in the spectra of N type stars

Shajn, G.A. and შაინი, გ. (1942) The occurrence of carbon isotopes in the spectra of N type stars. აბასთუმნის ასტროფიზიკური ობსერვატორიის ბიულეტენი / Bulletin of the Abastumani Astrophysical Observatory (6). pp. 1-16.


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Introduction. The problem of isotopes is of considerable interest for astronomy. Thus the relative abundance of several isotopes may be predicted by the theory, since in the statistical equilibrium the concentration of each nucleus in the known cyclical reaction is proportional to its lifetime. For instance, On captures slow protons about 70 times as easily as C12, therefore C" should be 70 times as abundant. This must hold at least in the interior of stars. If the relative abundance of isotopes does not depend on the nuclear reactions mentioned above, the general presumption that the isotopes of carbon will be found everywhere in the same proportion (nearly 70: 1) can hardly be applied to stars of type N and R, the relative abundance of elements, at least of carbon and oxygen, being quite unusual in these stars. Further, it is brought out from the few laboratory experiments by King that the intensity ratio of the band C12C12 to C13C13 for the transition (1,0) depends on the conditions of excitation. If this is really so, an information may be obtained with respect to the physical conditions within N and R stars. In any case it is highly desirable to test this unexpected and mysterious result by means of astronomical data. Carbon generally deserves great attention owing to its peculiar role in the stars. The carbon branch of late type stars characterized by the relative excess of carbon as compared to oxygen was discovered long ago. More recently Beals manifested the existence of two parallel sequences in Wolf Rayet stars designated as the carbon and nitrogen sequence respectively, For some reasons it is more difficult to judge about any branching with respect to the carbon in the intermediate classes, but it may be mentioned that L. Berman was able to discover a carbon star of type Go (R Cor. Bor.). The isotopic effect for atoms (except hydrogen) is so feeble that it cannot bi-detected in stellar spectra. But in the case of molecules, when we are dealing with motion of heavy nuclei, the isotopic shift reaches often several tens of angstrom. As a result we shall have the shift of bauds as a whole and of the lines of bands which shall be in each case in first approximation proportional to the distance from the band (0,0) and the line (0,0) respectively. In view of the blending effect and the lowering of the continuous background the study of C13 C13 bands is much more difficult. We have found arguments in favour of the presence of the Isotope bands (0,1), (1,2). For other stars of our list the observed position for (0,1) is too far from the theoretical one to be identified with C13C13. As to the sequence 4-th there is observed a good agreement with theory for the Cl3C13 band (1,0), though the blending effect seems to be present. An anomaly may be indicated: the bands (0,1) and (1,0) are clearly fainter than it follows from the elementary statistics (except Y Can. Yen.). It is noticed that the intensity anomalies observed in X type stars may be interpreted partly in terms of the curve of growth and partly in the light of King's laboratory results. The observations give in my opinion convincing evidences favour of the existence of heavy molecules C12C12 in great concentration. The relative abundance of heavy molecules C12C12 was found to vary from star to star within the limits 0.1--1.0; in the terms of elementary statistics this corresponds to the variation of the abundance of isotope C13 within limits 0.05—0.50. It is shown that the criticism of the hypothesis of .the high relative concentration of C13C13 and C13 rests upon unsounded observational and theoretical basis. In the spectrum of the uniquely known hot carbon star (R Cor. Bor.) there is no trace of Isotope bands. An attempt to find the isotopic effect in the solar spectrum also proved to be unsuccessful. It is noticed that spectroscopic observations of red giants of type X testify that Bethe's cyclical reaction is not realized in these stars. 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 10:12
Last Modified: 16 Jul 2018 10:12

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