The relationship between stellar visual surface brightness and colour

Synthetic stellar spectra, computed for model stellar atmospheres for giant stars $$6000 K \geqslant T _{eff} \geqslant 4000 K$$ and for a Vega model, are used to study the dependence of stellar visual surface brightness (F_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 F_v–(B–V), F_v–(V–R) and F_v–(R–I) diagrams and gravity effects occur in the F_v–(B–V) diagram. The combined effects of metal abundance and gravity are smallest in the F_v–(V–R) diagram and the relationship between F_v and (V–R) agrees very well with that found observationally by Barnes & Evans.