1997A&A...320..287W

We present interferometric λ3 mm continuum and 34s (2-1) line observations towards the star forming NGC 2024(south) molecular cloud core. The continuum of the prominent dust cores FIR5 and FIR6 is spatially resolved. FIR5 separates into a binary or disk-envelope system. We explore the physical characteristics of the cores by means of a radiative transfer modelling in spherical symmetry. Solutions with low bolometric luminosities (L_bol∼1-4L_☉) and massive envelopes (M_env∼a few 10M_☉) fit the long wavelength spectral energy distributions best. Dust compositions allowing for thick ice coatings provide better agreement with the dynamical mass estimates derived from the kinematics of the surrounding gas clumps. The ambiguity of the models is severely confined by a recent λ350 µm flux density limit from the Heinrich-Hertz-Telescope (M_env>5M_☉, L_bol<30-80L_☉). In all cases, the mass of the envelope exceeds limits on the mass of any embedded central object by order(s) of magnitude. The observations are suggestive of protostellar objects in their earliest phase of formation, with the bulk of their mass still to be accreted. The 34s line emission arises from two clump ensembles near to, and likely associated with these dense cores - however, the cores proper still escape detection in their molecular emission. This striking anti-correspondence is suggestive of freeze-out of elements onto the surface of dust grains.