Astron. Astrophys. 360, 683-698 (2000)

Infrared observations of hot gas and cold ice toward the low mass protostar Elias 29 ^*

A.C.A. Boogert ^1,2, A.G.G.M. Tielens ^1,2, C. Ceccarelli ³, A.M.S. Boonman ⁴, E.F. van Dishoeck ⁴, J.V. Keane ¹, D.C.B. Whittet ⁵ and Th. de Graauw <sup>2

1</sup> Kapteyn Astronomical Institute, P.O. Box 800, 9700 AV Groningen, the Netherlands
² SRON, P.O. Box 800, 9700 AV Groningen, the Netherlands
³ Laboratoire d'Astrophysique de l'Observatoire de Grenoble, B.P. 53X, 38041 Grenoble Cedex, France
⁴ Leiden Observatory, P. O. Box 9513, 2300 RA Leiden, the Netherlands
⁵ Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, NY 12180, USA

Received 28 February 2000 / Accepted 9 May 2000

Abstract

We have obtained the full 1-200  spectrum of the low luminosity (36 ) Class I protostar Elias 29 in the  Ophiuchi molecular cloud. It provides a unique opportunity to study the origin and evolution of interstellar ice and the interrelationship of interstellar ice and hot core gases around low mass protostars. We see abundant hot CO and gas, as well as the absorption bands of CO, , and "6.85 " ices. We compare the abundances and physical conditions of the gas and ices toward Elias 29 with the conditions around several well studied luminous, high mass protostars. The high gas temperature and gas/solid ratios resemble those of relatively evolved high mass objects (e.g. GL 2591). However, none of the ice band profiles shows evidence for significant thermal processing, and in this respect Elias 29 resembles the least evolved luminous protostars, such as NGC 7538 : IRS9. Thus we conclude that the heating of the envelope of the low mass object Elias 29 is qualitatively different from that of high mass protostars. This is possibly related to a different density gradient of the envelope or shielding of the ices in a circumstellar disk. This result is important for our understanding of the evolution of interstellar ices, and their relation to cometary ices.

Key words: stars: formation stars: individual: Elias 29 ISM: dust, extinction ISM: molecules ISM: abundances infrared: ISM: lines and bands

* Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA.

Present address: California Institute of Technology, Downs Laboratory of Physics 320-47, Pasadena, CA 91125, USA

Send offprint requests to: A.C.A. Boogert (boogert@submm.caltech.edu)

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Contents

• 1. Introduction
• 2. Observations
  • 2.1. The 2.3-45 m spectrum
  • 2.2. The 45-190 m spectrum
• 3. Results
  • 3.1. The spectral energy distribution (SED)
  • 3.2. Ice and dust absorption bands
    • 3.2.1. H₂O ice
    • 3.2.2. CO ice
    • 3.2.3. ice
    • 3.2.4. The 3.47  band
    • 3.2.5. CH₃OH ice
    • 3.2.6. The 6.85  band
    • 3.2.7. Upper limits to solid , , , HCOOH, OCS, and `XCN'
    • 3.2.8. Silicates
  • 3.3. Gas phase absorption lines
    • 3.3.1. CO gas
    • 3.3.2. H₂O gas
• 4. Discussion
  • 4.1. Gas and solid state abundances
  • 4.2. The structure of Elias 29
• 5. Conclusions and future work
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: August 17, 2000
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