Astron. Astrophys. 326, 347-365 (1997)

A molecular line and infrared study of NGC 2264 IRS 1

K. Schreyer ¹, F.P. Helmich ², E.F. van Dishoeck ² and Th. Henning <sup>1

1</sup> Max Planck Society, Research Unit "Dust in Star-forming Regions", Schillergäßchen 2-3, D-07745 Jena, Germany
² Leiden Observatory, P.O. Box 9513, 2300 RA Leiden, The Netherlands

Received 22 November 1996 / Accepted 24 April 1997

Abstract

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 C¹⁸ O 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 55 K in a quite large inner cloud region (1 ), with even warmer gas ( 70 K) present close to IRS1 and the embedded star cluster. This warm cloud core is surrounded by extended material at a temperature of 20 to 30 K. Radiative transfer models applied for different molecules constrain the mean central density to 2 10⁶ cm^-3.

We estimated the beam-averaged total column densities at a number of grid positions around IRS1 from the C¹⁸ O 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 of 1 10^-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 CO and 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 and . These results suggest that NGC 2264 is in a somewhat later evolutionary stage.

Key words: ISM: clouds ISM: NGC 2264 cloud stars: formation radio lines: ISM infrared: ISM: continuum ISM: molecules

Send offprint requests to: K. Schreyer

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Contents

• 1. Introduction
• 2. Observations
  • 2.1. Infrared imaging
  • 2.2. Line observations
• 3. Images
  • 3.1. Infrared images
  • 3.2. HIRAS images
• 4. Results
  • 4.1. Integrated line maps
  • 4.2. The outflow
  • 4.3. Velocity structure
  • 4.4. Other species
• 5. Analysis
  • 5.1. Temperature
  • 5.2. Density
  • 5.3. Column density and CS abundance
  • 5.4. Mass estimates
• 6. Chemistry
  • 6.1. Column densities
  • 6.2. Abundances
• 7. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1997

Online publication: April 20, 1998
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