SIMBAD references

The standard deviation δm of the variations in magnitude due to microlensing is calculated for the case when the angular radius (θ_s) of the source is much larger than that of the Einstein ring (θ_o) for the microlens, (θ_s≥5θ_o ). An external shear γ different from zero is included in the calcuations. We find that a shear term usually has the effect of reducing the value of δm, and in all cases δm is smaller than the analytical approximation for the case γ=0 given by Refsdal and Stabell (1991A&A...250...62R), (RS). Thus the approximation can still be used to estimate an upper limit of the source size if δm is available from observations. We argue that microlensing effects on the radio core of QSO 0957+561 may be of importance for the modelling of that system, and hence for the value of the Hubble parameter, even if the core radius is as large as one light year.