Astronomy and Astrophysics – Astronomy
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...210.1708w&link_type=abstract
American Astronomical Society Meeting 210, #17.08; Bulletin of the American Astronomical Society, Vol. 39, p.118
Astronomy and Astrophysics
Astronomy
Scientific paper
The NGC 2024 region in Orion B produces intense continuum emission at millimeter and submillimeter wavelengths. Mezger et al. 1988 (A&A, 191, 44) detected a ridge of emission containing a number of compact sources which they named FIR 1 through FIR 6. In modeling the emission with three temperature components, they obtained a very low temperature of 16 K for the FIR cores and concluded that the cores were massive protostars. Their low core temperatures have been challenged and the protostellar nature of the cores remains controversial. We present here maps of the NGC 2024 ridge in four transitions of formaldehyde, namely 3(03) - 2(02) at 218.2222 GHz, 3 (22) - 2(21) at 218.4756 GHz, 5(05) - 4(04) at 362.7360 GHz, and 5 (23) - 4(22) at 365.3634 GHz. We use H2CO line ratios in LTE and LVG models to obtain temperatures and densities for the cores and their surroundings. We find high temperatures for the cores (45 to 85 K) and similar high temperatures for the surrounding ridge gas. These results are consistent with the picture that the entire region, ridge and cores, is heated by the radiation field of the neighbouring star cluster. Core densities are typically 106 cm-3. Making use of 850 μm fluxes from Johnstone et al. 2006 (ApJ, 639, 259) and our new temperatures, we find masses of the FIR clumps ranging from about 1 to 5 solar masses, much lower than the original estimates. We apply the virial theorem to four of the cores, FIR 3 - 6, and find that all four are unstable against collapse.
Mitchell George F.
Watanabe Tomomi
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