The Villafranca catalog of Galactic OB groups - I. Systems with O2–O3.5 starsJ. Maíz Apellániz, P. Crespo Bellido, R. H. Barbá, R. Fernández Aranda and A. SotaA&A, 643 (2020) A138DOI: https://doi.org/10.1051/0004-6361/202038228
