Radiation transfer of models of massive star formation. III. the evolutionary sequence

Abstract

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 Mc, Σcl, and β c are constructed. We find that in a fiducial model with Mc= 60 M Σcl = 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 Σcl, with higher temperatures in a higher Σcl core, but only weakly on Mc. 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 Σcl and β c (which determines disk size) are discussed. We find that, despite scatter caused by different Mc, Σcl, 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. © 2014. The American Astronomical Society. All rights reserved..