2. Selection of the sample, observations and data reduction
The selection of the stars was based on their spectral type. As an initial choice, we have adopted values published in the literature. To have an independent check on the effective temperature of the selected stars, we have used the Strömgren photometry provided by the ESO catalogues of the LTPV project. Then, we have placed the stars in the dereddened color-color [m1]-[c1] diagram (see Strömgren 1966), and compared their position with the theoretical colors from model atmospheres (Kurucz 1992). As a result, we derived a sample of seven stars with spectral types between F5 and A5: V346 Ori, V351 Ori, BF Ori, BN Ori, NX Pup, HD 35929, and AK Sco.
The photometric observations were performed in two runs with different telescopes at ESO, La Silla. In the first period (Dec. 23-29, 1998), we used the 0.5k0.5k CCD (Tektronix TK512CB) attached to the 0.9m DUTCH telescope. Five of the seven nights were photometric. In the second period (June 30 to July 4, 1999) we used the 2k2k CCD (LORAL/LESSER) attached to the 1.5 m. DANISH telescope. Unfortunately, weather conditions were excellent for accurate photometric observations only during one night. Due to their brightness, all of the sources are suitable for observations in the Strömgren uvby-system. Two comparisons stars were used for each candidate variable; whenever possible, we observed the same comparison stars as in the LTPV program. Data reduction and analysis to derive instrumental aperture magnitudes were performed following the standard procedures under the MIDAS environment. The typical intrinsic instrumental photometric error in each Strömgren filter is of the order of a few thousands of a magnitude.
© European Southern Observatory (ESO) 2000
Online publication: March 21, 2000