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Published online by Cambridge University Press: 02 August 2017
The abnormal weakness of the hydrogen lines in the spectra of the stars of the R CrB type has been long known. Berman's work on the spectrum of the prototype established the presence of strong high-level absorption lines of neutral carbon and of weak bands of C2, and his analysis of the spectrum, carried out by the method of curve of growth, led him to conclude that carbon is by far the most abundant element in the atmosphere of R CrB, and that hydrogen is greatly deficient. Recent work at the McDonald Observatory has shown that in addition to the high-level lines of neutral carbon, other lines arising from very high levels of neutral oxygen and neutral nitrogen are also present in unusual strength in the visual region of the spectrum of this star. The presence of these other high-excitation lines strongly suggests that reliable values of the relative abun¬dances of the elements C, N, and O in the R CrB stars must await detailed studies using the method of model stellar atmospheres.