Stellar distance (pc) versus colour (B − V, as an indicator of spectral type). Key to symbols: blue filled circles: Serendipitously-observed stars in the CVS sample; red diagonal crosses: Target stars in the CVS sample; black dots: all Tycho stars with 2XMM light-curves; grey dots: all Tycho stars falling in 2XMM fields (without regard to 2XMM detection). For the last two classes, some points lie outside the plot and are therefore omitted, in order to improve visibility of the main distribution.