tokens: The gas line emission from the J = 3 – 2 transitions of three CO isotopologues, 13 CO (330.588 GHz, Klapper et al. 2000 ), C 18 O (329.331 GHz, Klapper et al. 2001 ) and C 17 O (337.061 GHz, Klapper et al. 2003 ) were extracted from the dataset, using the entire pixel map, after the lines were identified. The source A LSR velocity of 3.1 km s −1 ( Jørgensen et al. 2011 ) was used for all lines. Channels within ±5 km s −1 of each line were combined into an integrated intensity (moment zero) map for each isotopologue, using the image analysis software MIRIAD. Using this approach, the vast majority of the observed line emission was extracted, while avoiding major line-blending from other species. Figure 2 shows the integrated intensity maps of the three isotopologues. C 17 O appears to trace the dust distribution fairly well, as does the C 18 O emission. 13 CO, however, shows a markedly different emission structure, which is likely attributable to optical depth effects, where only the outer layer of the 13 CO structure is probed. Absorption toward source B is evident in all lines but to a smaller extent in C 17 O, revealing that C 17 O is the line with the lowest optical depth, as expected since it has the lowest abundance ( Wilson Rood 1994 ). An interesting feature is the broad emission arc between the sources, which is also present in the dust continuum emission, suggesting a common origin of both the dust and gas emission in this region. We focused on the overall structure of the emission and left a more detailed analysis of the gas kinematics to a future paper (Van der Wiel et al., in prep.). 3 Dust radiative transfer modeling This section describes the setup of the radiative transfer code RADMC-3D, including a description of the dust opacity, model grid and the envelope dust density model used. At the end of the Section, we present our investigation of the temperature structure difference between a single- and a binary protostar, where the envelope dust density model was used. We constructed 3D dust and gas line radiative transfer models consisting of a large envelope with a radius of 8 × 10 3 AU based on Schöier et al. (2002) , two disks around the protostars, as well as a dust filament between the two protostars. The disk’s dust densities were modeled with both the model protoplanetary disk (PP-disk) structure known from Class II sources (e.g., Andrews et al. 2012 ) and the density solution from the angular momentum conservation of an infalling, rotating collapse ( Terebey et al. 1984 ). This infalling, rotating collapse density structure is hereafter referred to as a rotating toroid model, based on the toroidal shape appearing at the centrifugal radius ( Terebey et al. 1984 ), which is the radius where the infalling material with the largest angular momentum impacts the midplane. In terms of luminosity, all models, whether they used one or two radiation sources, were limited to a total luminosity of 21 L ⊙ . This luminosity is based
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