2. Observations

The observations were carried out during the period 7-21 April 1994, using the modular photometer (Kilkenny et al. 1988) on the 0.5-m telescope at the Sutherland site of the South African Astronomical Observatory (SAAO), with a pulse-counting system and a set of SAAO filters. The observations were calibrated to the standard system using standard stars from the lists of Cousins (1987), Perry et al. (1987), Crawford et al. (1971) and Olsen (1983), to cover as large a range as possible of b-y, m₁, c₁ and and to avoid extrapolation in the color equations. The reduction to the standard system was carried out by the procedure adopted at SAAO.

There are two other extensive uvby lists of stars in Carina region. The presented sample contains 18 stars in common with Knude (1992) and 14 with Shobbrook & Lynga (1994) (hereafter S&L). Mean differences in V, b-y, m₁, c₁ and in the sense (this paper minus others) are shown below (the mean s.e. is of order of 0.001).

V b-y m₁ c₁

Knude 0.003 0.001 0.027 0.005 -0.01

S&L 0.009 0.007 0.031 0.009 0.004

These sets agree quite well in V, b-y, c₁ and but there is a systematic difference in m₁. The reduction of the m₁ values obtained in this paper to the standard system was carried out both using (v-b) and (b-y) colors and m₁ color differences. The standard stars residuals do not show any systematic differences in both cases. Only a few stars with very negative values of m₁ are outside the range of the standard stars. For the range of comparison with the lists of Knude (1992) and Shobbrook & Lynga (1994), the extrapolation in the color equations is fully avoided and any sources of systematic errors in this set of data cannot be seen. This quantity is not used in E(b-y) nor in M_v calculations and therefore does not influence the results. Differences of this order in V, c₁ and leads to an error of ± 0.2 mag in the M_v determination.

The uvby photometry for the program stars is given in Tables 1a (Car OB1 - 50 stars) and 1b (Car OB2 - 80 stars). The stars are referred to these two fields according to their values of galactic longitude l.