The effect of stellar spots on the colour and apparent lithium abundance of stars

A simple two-temperature model is developed to investigate the effect of stellar spots on the apparent magnitude and apparent lithium abundance of the star. For appropriate coverage factors, stellar spots can cause considerable variations in the apparent magnitude (about ±0.2 mag in V band and about −0.1 mag in B−V band) and equivalent width of LiI λ6708Å (about −0.2−0.3 dex). In comparison with normal, spot-free stars, spotty stars exhibit bluer B−V colours, and narrower LiI λ6708Å lines. Form the observed amplitude of luminosity variation, the change of spot coverage on the apparent disk ΔFs can be estimated to range from a few percent to 20%, hardly ever exceeding 30%.