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Published online by Cambridge University Press: 12 April 2016
Recent advances in high S/N spectroscopy are reviewed with particular emphasis on new data for the abundances of chemical elements of importance for the modelling of stellar interiors.
It seems well established that young, nearby B-type stars have abundances of CNO elements that are about a factor of two lower than in the Sun except for a small fraction of nitrogen-rich stars. The existence of such stars among main sequence stars remains to be explained.
Among normal A-type stars (excluding Am and Ap stars) large deviations from solar abundance ratios occur with interesting anticorrelations of the abundances of C and Si. This suggests that diffusion processes and/or gas-dust separation of the chemical elements in the protostellar cloud play an important rôle.