HIGH-RESOLUTION STUDIES OF PROTOSTELLAR CONDENSATIONS IN NGC-2024

We present interferometric lambda 3 mm continuum and (CS)-S-34 (2 - 1) line observations towards the star forming NGC 2024 (south) molecular cloud core. The continuum of the prominent dust cores FIR 5 and FIR 6 is spatially resolved. FIR 5 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 wi th low bolometric luminosities (L-bol similar to 1 - 4 L.) and massive envelopes (M-env similar to a few 10 M.) fit the long wavelength spec tral energy distributions best. Dust compositions allowing for thick i ce coatings provide better agree ment with the dynamical mass estimate s derived from the kinematics of the surrounding gas clumps. The ambig uity of the models is severely confined by a recent lambda 350 mu m fl ux density limit from the Heinrich-Hertz-Telescope (M-env > 5 M., L-bo l < 30 - 80 L.). 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 earli est phase of formation, with the bulk of their mass still to be accret ed. The (CS)-S-34 line emission arises from two clump ensembles near t o, and likely associated with these dense cores - however, the cores p roper still escape detection in their molecular emission. This strikin g anti-correspondence is suggestive of freeze-out of elements onto the surface of dust grains.