Galactocentric velocity vs. Galactic longitude. The points represent the mean values of V_GC for samples binned in Galactic longitude. The respective error bars stand for the standard error of the mean computed as , where N is the number of points in the respective bin. The black line shows a linear fit of the full NSD sample, the orange line for stars with [Fe/H] > 0.3, the red line for MR stars with [Fe/H] > 0, the blue line for stars with [Fe/H] < 0, the green line for stars with −0.5 < [Fe/H] < 0, and the magenta line for stars with [Fe/H] < −0.5. The dash-dotted lines show the corresponding APOGEE bulge sample (see text). The two green areas indicate the approximate radius of the NSD.