Astron. Astrophys. 330, 711-725 (1998)

Ice CO-cktails in molecular cloud cores

T.C. Teixeira ¹, J.P. Emerson ¹ and M.E. Palumbo <sup>2

1</sup> Department of Physics, Queen Mary and Westfield College, Mile End Road, London E1 4NS, UK
(t.c.teixeira@qmw.ac.uk and j.p.emerson@qmw.ac.uk)
² Osservatorio Astrofisico di Catania, V.le A. Doria 6, I-95125 Catania, Italy (mepalumbo@alpha4.ct.astro.it)

Received 3 September 1996 / Accepted 16 September 1997

Abstract

Spectra of the 4.67 m (2140 cm^-1) solid-CO absorption feature are presented, towards embedded low mass Young Stellar Objects in nearby molecular cloud cores, mostly in Taurus. The likely composition of the CO-bearing ices is analysed by fitting the observations with laboratory data and the statistical significance of the results is discussed. Excellent fits to the nonpolar component of the CO-ices along the observed lines of sight are produced with irradiated pure CO ices, as previously suggested by Palumbo & Strazzulla (1993). It does not seem to be possible, however, to constrain the composition of the polar component by analysis of the CO band only. The possible origin of the ion irradiation is discussed. The implications of the non-uniqueness of the fit on the determination of the abundance ratio between nonpolar and polar CO-ices are noted. Future observations are suggested to discriminate between the different possibilities for the polar component. Predictions are made for the abundance of CO₂ and methanol in the mantles.

Key words: circumstellar matter stars: formation stars: pre-main sequence ISM: dust, extinction, ISM: molecules infrared: ISM: lines and bands

Send offprint requests to: J.P. Emerson

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Contents

• 1. Introduction
• 2. Observations
  • 2.1. General description
  • 2.2. Data reduction
  • 2.3. The spectra
• 3. Analysis of the band
  • 3.1. The laboratory spectra
  • 3.2. The fitting procedure
  • 3.3. mapping
  • 3.4. O₂ -rich ices
• 4. Energetic processing of the ice mantles
  • 4.1. Flares
  • 4.2. Low energy cosmic rays
  • 4.3. UV and X-ray processing
• 5. Column densities
  • 5.1. Estimates from the best fits
  • 5.2. Ratio of nonpolar to polar CO-ices
  • 5.3. CO₂ and CH₃ OH abundances
• 6. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1998

Online publication: January 16, 1998
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