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Astron. Astrophys. 362, 245-254 (2000)

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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 [FORMULA] Tucanae, was the same for each colour as it is described in Paper I. The magnitude difference between the comparison stars, [FORMULA][FORMULA] and [FORMULA][FORMULA], 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

[EQUATION]

and for the differential light curve of comparisons an adjustment

[EQUATION]

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.

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© European Southern Observatory (ESO) 2000

Online publication: October 30, 19100
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