MS curve is represented with a thick blue line . Colored circles indicate the source is situated within 2.2 and 4.2 kpc, while gray dots show stars with distances lower than 2.2 kpc or higher than 4.2 kpc. Thinner blue lines enclose the selected region (see Sect. 3). Massive star candidates are shown with blue circles and labels indicate their previous ST classification. Small yellow circles are potential low-mass stars. Discarded sources are represented by green circles.