The relationship between stellar visual surface brightness and colour

Synthetic stellar spectra, computed for model stellar atmospheres for giant stars 6000 K >= Tsub(eff) >= 4000 K and for a Vega model, are used to study the dependence of stellar visual surface brightness (Fsub(v)) on colour. The agreement with observational correlations for Population I stars appears to be quite satisfactory. The models show that whilst the basic relationship is a thermal one, metal abundance effects do occur in the Fsub(v)-(B-V), Fsub(v)-(V-R) and Fsub(v)-(R-I) diagrams and gravity effects occur in the Fsub(v)-(B-V) diagram. The combined effects of metal abundance and gravity are smallest in the Fsub(v)-(V-R) diagram and the relationship between Fsub(v) and (V-R) agrees very well with that found observationally. (author)