Radiation Transfer of Models of Massive Star Formation. III. The Evolutionary Sequence

We present radiation transfer simulations of evolutionary sequences of massive protostars forming from massive dense cores in environments of high mass surface densities, based on the Turbulent Core Model. The protostellar evolution is calculated with a multi-zone numerical model, with the accretion rate regulated by feedback from an evolving disk wind outflow cavity. The disk evolution is calculated assuming a fixed ratio of disk to protostellar mass, while the core envelope evolution assumes an inside-out collapse of the core with a fixed outer radius. In this framework, an evolutionary track is determined by three environmental initial conditions: the core mass M_c , the mass surface density of the ambient clump Σ_cl, and the ratio of the core's initial rotational to gravitational energy β _c . Evolutionary sequences with various M_c , Σ_cl, and β _c are constructed. We find that in a fiducial model with M_c = 60 M _⊙, Σ_cl = 1 g cm^-2, and β _c = 0.02, the final mass of the protostar reaches at least ~26 M _⊙, making the final star formation efficiency >~ 0.43. For each of the evolutionary tracks, radiation transfer simulations are performed at selected stages, with temperature profiles, spectral energy distributions (SEDs), and multiwavelength images produced. At a given stage, the envelope temperature depends strongly on Σ_cl, with higher temperatures in a higher Σ_cl core, but only weakly on M_c . The SED and MIR images depend sensitively on the evolving outflow cavity, which gradually widens as the protostar grows. The fluxes at <~ 100 μm increase dramatically, and the far-IR peaks move to shorter wavelengths. The influence of Σ_cl and β _c (which determines disk size) are discussed. We find that, despite scatter caused by different M_c , Σ_cl, β _c , and inclinations, sources at a given evolutionary stage appear in similar regions of color-color diagrams, especially when using colors with fluxes at >~ 70 μm, where scatter due to inclination is minimized, implying that such diagrams can be useful diagnostic tools for identifying the evolutionary stages of massive protostars. We discuss how intensity profiles along or perpendicular to the outflow axis are affected by environmental conditions and source evolution and can thus act as additional diagnostics of the massive star formation process.