SIMBAD references

A modified method of computer reduction of UBV (or uvby) photoelectric observations to standard systems, which combines advantages of what has so far been achieved in this area, is described in detail. A complete reduction of over 46000 UBV observations obtained at Hvar Observatory between 1972 and 1991, and of nearly 5000 UBV observations secured at Skalnate Pleso Observatory between 1980 and 1987, was carried out using the new technique. It is argued that replacing the original Johnson's UBV values for the non-variable stars that were observed by the mean values based on repeated observations over several years and applying the new reduction technique can ensure a stable reproduction of UBV magnitudes, obviously quite close to the standard Johnson's ones, over many years and from observatories situated at very different altitudes above sea level within about 0.01mag in all three UBV magnitudes. A list of new accurate mean UBV values of 191 stars which were regularly observed at Hvar - and a part of them also at Skalnate Pleso - as comparison, check and standard stars in the Be- and Ap-star observing programs, is included for future use by photometric observers in the Northern Hemisphere. For a number of these stars, we can guarantee secular constancy within 0.mag01 during the past 5 to 15 years.