...observations

Based on observations made with the Isaac Newton and Nordic Optical Telescopes, which are operated on the island of La Palma by the Isaac Newton Group and the NOT Scientific Association, respectively, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.

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...IRAF

IRAF is distributed by National Optical Astronomical Observatories, which is operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation, U.S.A.

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...bars

For the measurements by Pilachowski et al. 1993, we compute the errorbars from the SNR values provided by C. Pilachowski (private communication) and using $\sigma=1.6({\rm FWHM}\delta x)^{1/2}/$SNR (Cayrel 1988), where $\delta x$ is the dispersion per pixel and SNR the signal to noise ratio.

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