Nature of two massive protostellar candidates: IRAS 21307+5049 and IRAS 22172+5549

We present observations of continuum and molecular lines towards the protostar candidates IRAS 21307+5049 and IRAS 22172+5549. Single-dish maps in the 12CO (2-1), 13COI (2-1), HCO+I (1-0) lines and 850 μm continuum are compared with interferometric maps in the 12CO (1-0) line and 3 mm continuum, and with mid- and near-infrared images. Also, single-pointing spectra of the CH3C2H (6-5), (8-7) and (13-12) lines observed towards IRAS 21307+5049, and H2 and [FeII] line emission observed towards IRAS 22172+5549, are presented. A plausible interpretation of our data based on the continuum maps and spectral energy distributions is that two components are present: a compact molecular core, responsible for the continuum emission at wavelengths longer than ∼25;μm, and a cluster of stars located close to the center of the core, but not spatially coincident with it, responsible for the emission at shorter wavelengths. The core is approximately located at the center of the associated molecular outflow, detected for both sources in the 12CO (1-0) and (2-1) lines. The cores have masses of ∼50;M⊙, and luminosities of ∼103;L⊙. The outflows parameters are consistent with those typically found in high-mass young stellar objects. Our results support the hypothesis that in these sources the luminosity is dominated by accretion rather than by nuclear burning. We conclude that the sources embedded inside the cores are likely protostars with mass ∼ 5-8;M⊙.