2025MNRAS.541.1286U

In this study, we present a detailed abundance analysis of 12 OB stars in the Orion Nebula (M42), a star-forming region. High- and medium-resolution spectra of these target stars were obtained from the Ankara University Kreiken Observatory, TÜBİTAK National Observatory, and the archives of the European Southern Observatory. The atmospheric parameters of each star were estimated from the hydrogen Balmer, ionized silicon, and/or helium lines. Non-local thermodynamic equilibrium model atmosphere calculations were employed to derive precise elemental abundances of helium, carbon, nitrogen, oxygen, neon, magnesium, aluminum, silicon, sulphur, and iron from the stellar spectra of each target. The analysis revealed that early B-type stars within the M42 star-forming region are chemically homogeneous. The identification of chlorine spectral lines in HD 37356 further motivated a broader investigation into chlorine abundances in early B-type stars beyond the M42 region-specifically in $\epsilon$ CMa, $\gamma$ Peg, and HD 135485, all of which were found to exhibit chlorine overabundance relative to the solar value. Additionally, the masses and ages of all target stars were estimated using evolutionary tracks and isochrones appropriate to the physical characteristics of each star.