The Villafranca catalog of Galactic OB groups. I. Systems with O2-O3.5 stars

J.M.A. and A.S. acknowledge support from the Spanish Government Ministerio de Ciencia through grants AYA2016-75 931-C2-2-P and PGC2018-095 049-B-C22. R.H.B. acknowledges support from DIDULS Project 18 143 and the ESAC visitors program. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium).Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. Additionally, this paper includes data obtained with the MPG/ESO 2.2m Telescope at the Observatorio de La Silla, Chile; the 2.5m du Pont Telescope at the Observatorio de Las Campanas, Chile; the 10m HobbyEberly Telescope at McDonald Observatory, Texas, USA; the 4.2m William Herschel Telescope and the 10.4m Gran Telescopio Canarias at the Observatorio del Roque de los Muchachos, La Palma, Spain; and the 2.2m Telescope at the Centro Astronomico Hispano Andaluz, Almeria, Spain. We thank the sta ff at those observatories for their support. This research has made extensive use of the SIMBAD and VizieR databases, operated at CDS, Strasbourg, France.