Columns 1 and 2 give the star identifiers, Cols. Table 4 presents the results of the best fits in the case that the energy distribution of the observed sdB star represents a binary system containing a hot subdwarf and a cool companion. It is easy to see that the presence of a cool companion in the system produces a flattened continuum in the redder wavelengths range due to the introduced infrared excess. In this way, the slope of the theoretical model atmospheres representing a composite system is flatter than the slope of a model representing a single star. The IUE spectra were rebinned at the sampling resolution of the model atmospheres.
Error bars are asymmetric because of the logarithmic scale.
In the case of a single subdwarf B star, the observed energy distribution is a function of several parameters, i.e., . In our multi-dimensional fitting procedure, the solution of the system will be more or less sensitive to the initial estimates of some particular atmospheric parameter. The internal errors associated with the best set of atmospheric parameters, provided by the -minimization procedure, are given by the diagonal elements of the inverse of the covariance matrix . For those parameters we make some assumptions for their standard errors. We assume to be 0.2 dex the standard error of the surface gravity, 0.01 is assumed for the interstellar extinction and 0.01 for the helium abundance.