2. The new data
We refer to Paper I for details on the instrumentation and journal of observations. The u,v and b magnitudes (1450 observations for each colour) collected simultaneously with the y magnitudes using SAT uvby photometer in Chile are discussed in Paper II. The new data in the present paper are 460 b magnitudes using the single-channel photometer attached to the South African Astronomical Observatory 0.5 m telescope at Sutherland during 13 nights obtained by M. Paparó. The reduction procedure, including a check for constancy of comparisons, homogenization of data and investigation of mean light level of Tucanae, was the same for each colour as it is described in Paper I. The magnitude difference between the comparison stars, and , shows the constancy of comparisons in b colour, too, and the fact that the zero point of the SAAO and ESO instrumental Strömgren systems are close to each other in b without any transformation. Nevertheless, because of the homogeneous treatment of colours a similar zero point shift procedure was applied for the SAAO b data as it is described in Paper I for y colour. The photometric zero-point of ESO system is accepted as the zero-point of the homogeneous b data set. For the different light curves an adjustment
and for the differential light curve of comparisons an adjustment
were accepted in b . After the zero-point shift the SAAO and ESO b mean light level values outline the same curve as it is shown in Fig. 2a of Paper I for y . The colour changes through the orbital cycle have been discussed in detail in Paper II and shown in Fig. 5. The v and u data were left in the ESO instrumental system. Our following analysis and results are based on more than 2300 y, almost 2000 b and b-y and almost 1500 u and v measurements which were treated homogeneously resulting in a homogeneous data set.
© European Southern Observatory (ESO) 2000
Online publication: October 30, 19100