Collapsing Hot Molecular Cores: A Model for the Dust Spectrum and Ammonia Line Emission of the G31.41+0.31 Hot Core

We present a model aimed to reproduce the observed spectral energy distribution (SED) as well as the ammonia line emission of the G31.41+0.31 hot core. The hot core is modeled as an infalling envelope onto a massive star that is undergoing an intense accretion phase. We assume an envelope with a density and velocity structure resulting from the dynamical collapse of a singular logatropic sphere. The stellar and envelope physical properties are determined by fitting the observed SED. From these physical conditions, the emerging ammonia line emission is calculated and compared with subarcsecond resolution VLA data of the (4,4) transition taken from the literature. The only free parameter in this line fitting is the ammonia abundance. The observed intensities of the main and satellite ammonia (4,4) lines and their spatial distribution can be well reproduced provided it is taken into account the steep increase of the gas-phase ammonia abundance in the hotter (> 100 K), inner regions of the core produced by the sublimation of icy mantles where ammonia molecules are trapped. The model predictions for the (2,2), (4,4), and (5,5) transitions, obtained with the same set of parameters, are also in reasonably agreement, given the observational uncertainties, with the single-dish spectra of the region available in the literature. The best fit is obtained for a model with a central star of ∼ 25 M⊙, a mass accretion rate of ∼ 3× 10 M⊙ yr , and a total luminosity of ∼ 2× 10 L⊙. The outer radius of the envelope is 30,000 AU, where kinetic temperatures as high as ∼ 40 K are reached. The gas-phase ammonia abundance ranges from ∼ 2 × 10 in