[en] The research into CNO isotopes in astrophysics includes many different subfields of astrophysics such as meteoretical studies, experimental and theoretical nuclear astrophysics, optical astronomy, radio astronomy, etc. The purpose of this paper is to give some overview of the topic and guideline among these different subfields. (G.T.H.)

[en] Since the independent suggestions in 1938 of Bethe (1939) and von Weiszaecker (1938) that captures of protons by carbon and nitrogen isotopes were the source of energy generation in stars, the CNO cycles have developed into what might be considered by some a many-cycled monster rivalling the many-headed Hydra. However, those of us who are researchers in nucleosynthesis have found the reactions of the CNO nuclei a fertile field. In this paper the many reactions that may occur are presented. (Auth.)

[en] In a recent study of the spectrum of the planetary nebula NGC 7027 (Panagia et al. 1976) the authors were able to determine both the amount of carbon contained in grains and the amount in a gaseous form. In this paper the most relevant results are presented and some implications on the late stages of the stellar evolution and the chemical evolution of the Galaxy are discussed. (Auth.)

[en] This paper summarizes the radio astronomical observations of carbon-containing molecules in the interstellar medium. The (¹²C/¹³C) isotope ratios derived from observations reported up to August 1976 are given. Except for the Orion Molecular Cloud, all H₂CO ratios were obtained from the 1₁₀-1₁₁ absorption line, at 4.8 GHz. The HC₃N data of Churchwell et al. (1976), were measured at 9 GHz. All other isotope results were obtained in the millimeter wavelength region. To minimize the possibility of saturation, the isotope ratios for CO, CS, and HCN were measured using two rarer species, such as ¹³C¹⁶O and ¹²C¹⁸O. (Auth.)

[en] Fractionation of carbon isotopes in interstellar clouds is treated in some detail. Acting together, the exchange reaction ¹³C⁺+¹²CO reversible ¹²C⁺+¹³CO+ΔE and the high vapor pressure of CO may cause a preferential loss of ¹²C from the gas due to freezing onto dust grains. The ¹³C/¹²C ratio for the carbon in the gas is then raised by factors approximately 2 to 4. Fractionation of deuterium is also discussed since the proposed process is similar to the carbon isotope exchange and here there is no question that fractionation is a major effect. Important information about physical conditions in dense clouds - the fractional electron density and CO abundance - can be derived from the fractionation process producing the enhanced DCO⁺/HCO⁺ ratio. Possible fractionation reactions for isotopes of other elements (oxygen, sulfur) are mentioned briefly. (Auth.)

[en] Mahoney, McCutcheon and Shuter (1976) reported observations of the J = 1 → 0 transition of three isotopes of CO in the dust cloud Lynds 134 using the 4.6 m telescope at Aerospace Corporation. In this paper a new observation of ¹²C¹⁷O is discussed and the question of the ratio ¹³C¹⁶O/¹²C¹⁸O across the dust cloud is considered further. (Auth.)

[en] The origin of the seven stable isotopes of carbon, nitrogen, and oxygen remains an unsolved problem. Current views as to the mechanisms of nucleosynthesis of these nuclei indicate a collective history which is extremely complex. Theoretical studies have revealed that quite varied astrophysical sites can contribute significantly to their production, including CNO-cycle hydrogen burning, core helium burning, thermal relaxation oscillations associated with double-shell-burning configurations in red giants, nova explosions, and supernova explosions. The relevance of detailed quantitative estimates of contributions from these diverse sites is clear from the discussions presented throughout this session: coupled to increasing observations of CNO elemental and isotopic abundances, such studies can yield important inferences concerning the history of the interstellar medium, the evolution of our galaxy and of other galaxies, the sources of cosmic rays, stellar evolution, and the mechanisms of nova and supernova explosions. (Auth.)

[en] Model stellar atmospheres have been constructed to investigate the effects of the continuous opacity of CI, NI and OI on the Balmer jump of late-B horizontal branch stars. The large opacity of CI and NI in the ultraviolet raises the Balmer continuum through back warming without changing the Paschen continuum, while OI has little effect. The models provide an explanation for the variations in the Balmer jump which have been observed from star to star by Oke near 12,500 ⁰K on the horizontal branch of the globular cluster M92. It is concluded that some stars in M92 appear to have an atmospheric C and/or N content between one hundred and one thousand times the cluster average. The same effect of the opacities of CI and NI may also explain Newell's gap NI in the [(U-B)-(B-V)]-diagram for blue stars in the galactic halo. (Auth.)

[en] The carbon and nitrogen abundances in the atmospheres of giant stars in the metal-poor globular cluster M92 are examined. (Auth.)

[en] Until recently no visible wavelength line of a secondary isotopic species of any atom or molecule had been detected in the interstellar medium with the sole exception of the lambda 4232 line of ¹³CH⁺ which is seen in absorption against zeta Oph. However, there are several problems with the data obtained from this line chiefly to do with the velocity components of the zeta Oph cloud. The authors therefore decided to observe the lambda 3957 line of CH⁺ toward zeta Oph. (Auth.)