Comparison between Hα EWs measured in this work and the Gaia DR3 ESP-ELS results (Creevey et al. 2023). Left: direct EW comparison for OC members with |(S/N)_Hα| > 1 and p_Hα > 0.95, colour-coded by |(S/N)_Hα|. The difference in sign convention (emission positive here and negative in Creevey et al. 2023) produces the anti-correlation. The green line indicates a slope of −2.3. Middle: probability distributions for different emission types (Be, Herbig Ae/Be, T Tauri, carbon and nitrogen Wolf–Rayet) from Creevey et al. (2023). Right: (S/N)_Hα versus (S/N)_Hβ coloured by ESP-ELS types; grey points without colour coding represent new emission candidates from this work.