Radiation Transfer of Models of Massive Star Formation. IV. The Model Grid and Spectral Energy Distribution Fitting

Abstract

We present a continuum radiative transfer model grid for fitting observed spectral energy distributions (SEDs) of massive protostars. The model grid is based on the paradigm of core accretion theory for massive star formation with pre-assembled gravitationally-bound cores as initial conditions. In particular, following the Turbulent Core Model, initial core properties are set primarily by their mass and the pressure of their ambient clump. We then model the evolution of the protostar and its surround structures in a self-consistent way. The model grid contains about 9000 SEDs with 4 free parameters: initial core mass, the mean surface density of the environment, the protostellar mass, and the inclination. The model grid is used to fit observed SEDs via χ 2 minimization, with the foreground extinction additionally estimated. We demonstrate the fitting process and results using the example of massive protostar G35.20-0.74. Compared with other SED model grids currently used for massive star formation studies, in our model grid, the properties of the protostar and its surrounding structures are more physically connected, which reduces the dimensionality of the parameter spaces and the total number of models. This excludes possible fitting of models that are physically unrealistic or that are not internally self-consistent in the context of the Turbulent Core Model. Thus, this model grid serves not only as a fitting tool to estimate properties of massive protostars, but also as a test of core accretion theory. The SED model grid is publicly released with this paper.

Discovery of a Photoionized Bipolar Outflow toward the Massive Protostar G45.47+0.05

“…This is further supported by the fact that the 1.3 and 7 mm continuum emissions coincide well with the H30α hydrogen recom- bination line (HRL) emission (Figure 2a; see below). Furthermore, the 1.3 mm peak brightness temperature is ∼ 2000 K, higher than that expected from dust continuum (the average dust temperature within 1000 au from a ∼ 30 M protostar is estimated to be several ×10 2 K from dust continuum radiative transfer (RT) simulations by Zhang & Tan (2018)) and the dust sublimation temperature (∼ 1600 K), but can be naturally explained by thermal emission from ionized gas with a typical temperature of 10 4 K around massive protostars. However, the extended 1.3 mm continuum emission shown in the low-resolution data should still be dominated by dust emission.…”

“…Figure 4 shows the observed SED from radio to nearinfrared. The infrared SED is well explained by dust continuum emission (De Buizer et al 2017) using the continuum RT model grid by Zhang & Tan (2018). Based on the same physical model, Rosero et al (2019) extended the model SED to radio wavelengths by combining photoionization and free-free RT calculations by Tanaka et al (2016) (thin lines in Figure 4).…”

“…Best-fit models for different opening angles (θw) are shown but the differences are small. The dust continuum models are from SED fitting by De Buizer et al (2017) using the dust continuum radiative transfer model grid by Zhang & Tan (2018). up a much larger amount of ambient gas (Tanaka et al 2017).…”

“…The protostar G45.47+0.05 (hereafter G45; d = 8.4 kpc, Wu et al 2019) has a luminosity of ∼ (2 − 5) × 10 5 L and a mass of ∼ 20 − 50 M (De Buizer et al 2017), based on infrared spectral energy distribution (SED) fitting (Zhang & Tan 2018). G45 is associated with an ultracompact (UC) H ii region (Wood & Churchwell 1989;Urquhart et al 2009;Rosero et al 2019) and OH and H 2 O masers (Forster & Caswell 1989).…”

Dynamics of a massive binary at birth

“…If dust grains survive in the ionized region, then the ionizing photon rates and stellar masses derived above are likely to be lower limits, due to absorption of Lyman continuum photons by the dust. However, the total bolometric luminosity of this system 2 ((1 − 4) × 10 4 L ) limits the masses of the two protostars < 20 M according to both ZAMS models 32 and protostellar evolution models 36 . Note that the ratio between the derived ZAMS masses of the two sources is 0.8, higher than that constrained from the source radial velocities and the cloud systemic velocity (< 0.50 ± 0.19).…”