Astron. Astrophys. 326, 373-385 (1997)

IRAS 12553-7651 in Chamaeleon II: a low mass PMS star with a C O outflow?

L. Olmi ¹, M. Felli ² and R. Cesaroni <sup>2

1</sup> Cornell University, Arecibo Observatory, P.O. Box 995 Arecibo, 00613, Puerto Rico
² Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy

Received 14 August 1996 / Accepted 2 April 1997

Abstract

We present new multi-line, multi-isotope observations of the PMS candidate IRAS 12553-7651 in the nearby Chamaeleon II dark cloud. Previous far infrared and molecular observations towards three selected objects in Cha II determined that IRAS 12553-7651 was the most likely candidate to be a young (proto)stellar object. We thus mapped the IRAS 12553-7651 region in the ¹² CO , ¹³ CO , and C¹⁸ O rotational transitions to use probes more sensitive to higher density gas and not affected by optical depth effects. We also observed and detected the C³⁴ S transition. Our observations confirm the presence of a high-density clump at the position of the IRAS source with  km s^-1, and reveal a C¹⁸ O velocity shift aligned along an axis SW-NE, of about 2 km s^-1 pc^-1, which is likely to be an outflow. Based upon this assumption, the ¹³ CO spectra of Olmi et al. (1994) have been re-analyzed and found to show a deviation from a Gaussian shape. This asymmetry can be interpreted in terms of a line component which migrates in velocity with respect to the ambient cloud. We show that a model in which the bipolar outflow interacts with the ambient gas around IRAS 12553-7651 may reproduce qualitatively the observational data.

Key words: interstellar medium: clouds: Chamaeleon II interstellar medium: molecules radio lines: interstellar

SIMBAD Objects

Contents

• 1. Introduction
• 2. Observations and data reduction
  • 2.1. System parameters
• 3. Results
  • 3.1. ¹² CO(2-1)
  • 3.2. ¹³ CO(2-1)
  • 3.3. C¹⁸ O(1-0)
  • 3.4. C³² S(2-1) and C³⁴ S(2-1)
• 4. Overview of the cloud components and their main physical parameters
  • 4.1. Definition of the main cloud components observed
  • 4.2. Excitation temperature
• 5. The "compact" molecular clump at  km s^-1
  • 5.1. Identification
  • 5.2. Mass and size
• 6. The "main" component at  km s^-1 and the bipolar outflow
  • 6.1. The evidence
  • 6.2. Abundance ratio and optical depth
    • 6.2.1. ¹³ CO to C¹⁸ O ratio
    • 6.2.2. Curve of growth analysis
  • 6.3. Other physical parameters
  • 6.4. Luminosity and dynamical time-scale
• 7. The drifting component and the interaction of the outflow with the ambient gas
  • 7.1. Energy requirements
  • 7.2. A simple model
• 8. Conclusions
• Acknowledgements
• Appendix A
• Appendix A: description of the model reproducing the ¹³ CO(1-0) profiles
• References

© European Southern Observatory (ESO) 1997

Online publication: April 20, 1998
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