Plan view of the Galactic disc showing the location of the sources in Table 1 (filled points) after recalculating their Galactocentric and heliocentric distances (Sect. 4.3). The Sun is marked by the red circled point, and the Galactic centre is pinpointed by the blue cross. The Solar circle is shown by the red dashed curve. The blue dotted circles correspond to Galactocentric distances of 10, 15, 20, and 25 kpc.