GSC 05685-03120 , the SIMBAD biblio

UBVRI photometry and MK spectral types have been obtained for a nearly complete sample of the massive star population of the Serpens OB2 association. This relatively neglected association is found to contain over 100 OB stars at a distance of 1.9±0.3 kpc and with a common age of 5±1 Myr. These stars illuminate the large H II region S54, and are directly connected to the unusual thermal ``chimney'' detected by Müller et al. Evidence is given of continuing star formation within the association, and the relationship between the association stars and the chimney is discussed.