Astronomy and Astrophysics – Astrophysics
Scientific paper
Feb 1988
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1988a%26a...191...44m&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 191, no. 1, Feb. 1988, p. 44-56.
Astronomy and Astrophysics
Astrophysics
129
Cosmic Dust, Molecular Clouds, Protostars, Stellar Evolution, Submillimeter Waves, Absorption Cross Sections, High Resolution, Infrared Radiation, Molecular Spectroscopy, Stellar Luminosity
Scientific paper
We have mapped the dust emission at λ = 1300 μm and λ = 350 μm in three cloud cores of high density (nH > 2 × 105 cm-3), whose masses range from ˜ 1 × 103 msun to 4 × 103 msun and which are associated with the source complexes NGC 2024 and S255IR. Observed with an angular resolution of < 30" the cloud cores exhibit considerable structure. Luminous stellar sources which are embedded in the cloud cores heat dust and gas in their surroundings to temperatures between 25-45 K. The bulk of gas and dust, however, is cold (Td ˜ 16 K). Embedded in the cloud core associated with NGC 2024 and close to its plane of symmetry we observe six high-density condensations (nH ˜ (108-109) cm-3) of cold gas and dust with stellar masses (˜ 10-60 msun) and typical sizes of ˜ (1016-1017) cm. They are surrounded by envelopes of lower density but with masses which are comparable to those of the high-density condensations. Comparison of their physical characteristics with computed evolutionary tracks of pre-MS stars suggests that these condensations are isothermal protostars without luminous stellar cores. Comparison with high-resolution molecular line observations suggest that molecules in these protostellar condensations are depleted, probably by accretion on dust grains. We estimate that at least one hundred of such massive isothermal protostars are observable with the 30 m MRT within a distance of ˜ 1 kpc from the sun. The integrated physical characteristics of the cloud cores in NGC 2024 and S255 IR are similar but the latter source complex is too far away for protostellar condensations to be observed. Our observations of NGC 2024 support the model by Crutcher et al. (1986) in which the high-density molecular gas (which accounts for approximately two thirds of the gas mass) is located behind the H II region.
Chini Rolf
Kreysa Ernst
Mezger Peter G.
Salter Christopher J.
Wink Jörn E.
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