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Astron. Astrophys. 320, 287-299 (1997)

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High resolution studies of protostellar condensations in NGC 2024

H. Wiesemeyer 1, R. G"usten 1, J.E. Wink 2 and H.W. Yorke 3

1 Max-Planck-Institut f"ur Radioastronomie, Auf dem H"ugel 69, D-53121 Bonn, Germany
2 Institut de Radio Astronomie Millimétrique, 300 Rue de la Piscine, F-38406 St. Martin d'Hères, France
3 Institut f"ur Astronomie und Astrophysik, Am Hubland, D-97074 W"urzburg, Germany

Received 29 July 1996 / Accepted 6 September 1996

Abstract

We present interferometric [FORMULA] 3 mm continuum and C34 S [FORMULA] 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 with low bolometric luminosities ([FORMULA]) and massive envelopes ([FORMULA] a few [FORMULA]) 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 [FORMULA] 350 µm flux density limit from the Heinrich-Hertz-Telescope ([FORMULA], [FORMULA]). 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 C34 S 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.

Key words: stars: formation – interstellar medium: dust – interstellar medium: molecules – interstellar medium: individual objects: NGC 2024 – radio continuum: ISM – radio lines: ISM

Send offprint requests to: H. Wiesemeyer

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© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998
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