Gaia DR3 CMD for sources in the NEMESIS Catalogue of YSOs in the OSFC (shown as black dots). Blue lines show isochrones for 1 Myr (continuous line), 10 Myr (dashed line) and 1 Gyr (dotted line). The reddening direction is indicated by the black arrow, which has an A_V = 1 mag length. Left: massive stars (Sect. 5.2.1) are shown as green dots. Likely MS and post-MS contaminants in our catalogue are shown as purple dots below a 20 Myr isochrone (yellow-dashed). Middle: sources are coloured by their Giant probability derived with a RF binary classifier in Appendix E. Right: sources with log ɡ collated from spectroscopic surveys (Sect. 2.3) are shown with coloured by their log ɡ measurement (Sect. 5.2.2).