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Globules and pillars, impressively revealed by the Spitzer and Herschelsatellites, for example, are pervasive features found in regions of massivestar formation. We studied the globule IRAS 20319+3958 in Cygnus X by means ofvisible and near-infrared imaging and spectroscopy, complemented withmid-infrared Spitzer/IRAC imaging, in order to obtain a census of its stellarcontent and the nature of its embedded sources. Our observations show that theglobule contains an embedded aggregate of about 30 very young ($\lesssim1$~Myr) stellar objects, for which we estimate a total mass of ~ 90 M_sun. Themost massive members are three systems containing early B-type stars. Two ofthem most likely produced very compact HII regions, one of them being stillhighly embedded and coinciding with a peak seen in emission linescharacterising the photon dominated region (PDR). Two of these three systemsare resolved binaries, and one of those contains a visible Herbig Be star. Anapproximate derivation of the mass function of the members of the aggregategives hints of a slope at high masses shallower than the classical Salpeterslope, and a peak of the mass distribution at a mass higher than that at whichthe widely adopted log-normal initial mass function peaks. The emissiondistribution of H$_2$ and Br gamma, tracing the PDR and the ionised gas phase,respectively, suggests that molecular gas is distributed as a shell around theembedded aggregate, filled with centrally-condensed ionised gas. Both, themorphology and the low excitation of the HII region, indicate that the sourcesof ionisation are the B stars of the embedded aggregate, rather than theexternal UV field caused by the O stars of Cygnus OB2. The youth of theembedded cluster, combined with the isolation of the globule, suggests thatstar formation in the globule was triggered by the passage of the ionisationfront.

Globules and pillars in Cygnus X. II. Massive star formation in the globule IRAS~20319+3958