Hydrogen fluoride has been used for generating reference absorption lines in coude spectra. This eliminates the systematic errors inherent in conventional radial velocity measurements, where the comparison beam does not follow exactly the same path as starlight. In a test of this method an accuracy of 15 m/s was achieved using sunlight. Pressure shifts have been measured for the HF 3-0 band R branch lines
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Campbell et al. (1979) studied this question.