SIMBAD references

An observational programme involving simultaneous CCD- and photoelectric uvbyβ photometry has been carried out using the two Danish telescopes at La Silla. In order to derive reliable astrophysical parameters for F dwarfs at distances of several kpc final accuracies better than 0.015mag for each magnitude are needed for faint stars. High accuracy requires careful preprocessing and data handling and the requested accuracy is now obtained for stars as faint as V≃18mag using the procedure described in this paper. A common robust CCD instrumental system is established and the subsequent transformation to the standard system is performed using a set of faint secondary standards observed in the photoelectric programme. Photoelectric photometry for a number of calibration stars in the CCD frames is also published. These stars have up to 11 observations each and may be included in the preliminary sample of secondary standards that has emerged from the combined programme.