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We investigate the influence of random motion of individual stars in the lensing galaxy on the light curve of a gravitationally lensed background quasar. We compare this with the effects of the transverse motion of the galaxy. We find that three-dimensional random motion of stars with a velocity dispersion σ in each dimension is more effective in producing "peaks" in a microlensed light curve by a factor α ~ 1. 3 than motion of the galaxy with a transverse velocity vₜ_ = σ. This effectiveness parameter α seems to depend only weakly on the surface mass density. With an assumed transverse velocity of vₜ_ = 600 km s^-1^ of the galaxy lensing the QSO 2237+0305 and a measured velocity dispersion of σ = 215 km s^-1^, the expected rate of maxima in the light curves calculated for bulk motion alone has to be increased by about 10% due to the random motion of stars. As a consequence, the average time interval DELTAt between two high-magnification events is smaller than the time interval DELTAtbulk_, calculated for bulk motion alone, DELTAt~0. 9DELTAtbulk_.
Kundić et al. (Mon,) studied this question.