The optical data presented in Table 1 were also compared with, mostly unpublished, optical positions with respect to the IRS Catalogue we have obtained for these objects. The same plate material was used for both determinations. This comparison yielded the following statistics: = -0.06, =0.17; ,; n = 24. Plots of the (Hipp-IRS) residuals as a function of the coordinates show clear systematic effects similar to those reported in Paper IV. This is not surprising considering that our Hipparcos referred optical positions are linked to the ICRS, therefore a comparison of these positions with IRS referred positions brings out the deviations of the IRS(FK5) system from the ICRS.
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