Astronomy and Astrophysics, volume 326, 347-365 (1997/10-1)
A molecular line and infrared study of NGC 2264 IRS 1.
SCHREYER K., HELMICH F.P., VAN DISHOECK E.F. and HENNING T.
Abstract (from CDS):
We present a study of the region around the intermediate-mass young stellar object NGC 2264 IRS1. This source is embedded in a dense cloud core. Infrared images in the J, H, and K band show a jet-like structure connected with IRS1 as well as a second very deeply embedded small star cluster to the southeastern side. IRS1 itself is surrounded by a number of embedded low-mass stars. We mapped this area in various CS transitions, CO 3->2, some methanol lines and in C18O 2->1. The mapping results clearly show a second cloud clump centered at the small star cluster. Two molecular outflows were found in the observed region. One flow is oriented along our line of sight and associated with IRS1 and the other flow is centered at the small star cluster. Several additional spectral line settings were taken at the IRS1 position to get more accurate constraints on the gas temperature and density. These data, as well as the maps, were analysed with statistical equilibrium excitation calculations. The best fit results give an uniform temperature of about 55K in a quite large inner cloud region (1'x1'), with even warmer gas (>70K) present close to IRS1 and the embedded star cluster. This warm cloud core is surrounded by extended material at a temperature of 20 to 30K. Radiative transfer models applied for different molecules constrain the mean central density to 2x106cm–3. We estimated the beam-averaged total H2 column densities at a number of grid positions around IRS1 from the C18O measurements. Using the modeled CS excitation, we can constrain the beam-averaged CS abundance distribution over the same area. The inferred CS abundance with respect to H2 of 1x10–9 is nearly constant over the whole region, and there is no indication for a CS depletion on this scale. Observations of a large number of other molecules have been obtained as well at the IRS1 position. The resulting abundances are compared to those found in other high- and low-mass young stellar objects. The abundances of the organic molecules H2CO and CH3OH are somewhat enhanced, whereas those of sulfur-bearing molecules are much lower. The most striking characteristic of the NGC 2264 chemistry is its nitrogen chemistry, especially the very high abundances of N2H+ and N2. These results suggest that NGC 2264 is in a somewhat later evolutionary stage.
ISM: clouds - ISM: NGC 2264 cloud - stars: formation - radio lines: ISM - infrared: ISM: continuum - ISM: molecules
p. 353: AFGL 2591 IRS 1 = [TGJ91] AFGL 2591 NIRS 1?
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