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Fig. 4

image

Left column: Goodness of fit values ΔQ for case A simulations. From top to bottom, the ΔQ values (grey bars) follow a χ2 distribution (red line) with five degrees of freedom. If the assumed radial velocities in the solution equal the true values, the actual and expected distributions agree perfectly. If the assumed radial velocity is unknown (set to zero) deviations from the expected distributions are seen. These outliers are caused by perspective acceleration. The markers in the quantile-quantile and scatter plots correspond to stars with radial velocities from XHIP (black dots) and to stars with random radial velocities (red crosses). The three rightmost red crosses in the scatter plots correspond to HIP 80190, HIP 80194, and HIP 67694 which have very large uncertainties in the Hipparcos Catalogue. Therefore they do not show a large ΔQ value even though they have large perspective acceleration. Right column: same plots for case B simulations (see Sect. 2.5).

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