Fig. 18.

Top: absolute V magnitudes computed from HIPPARCOS photometry but with Gaia DR2 parallaxes (MV = HPmag + 5log(Plx/100)) as a function of the HIPPARCOS B − V colour of 74 Ap stars with positive parallaxes in both catalogues. The symbols are the same as used in Figs. 12 and 15. Bottom: HIPPARCOS parallaxes HPlx were used to compute the absolute magnitudes (MV = HPmag + 5log(HPlx/100)). The labelled object (HD 81009) is not shown in the top panel because its Gaia DR2 parallax is negative.
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