Astron. Astrophys. 336, L53-L56 (1998)

Letter to the Editor

[C II] 158 and [O I] 63 µm ISO-Observations of L1457 ^*

Ralf Timmermann, Benedikt Köster and Jürgen Stutzki

Universität zu Köln, I. Physikalisches Institut, Zülpicher Strasse 77, D-50937 Köln, Germany

Received 4 May 1998 / Accepted 27 June 1998

Abstract

We report here the results of [C ii] 158 and [O i] 63 µm fine-structure line observations along two cuts across a molecular clump of L1457 (MBM 12) carried out with ISO-LWS. [C ii] emission was detected at all positions observed. It can be assigned to the cooling of the diffuse atomic interstellar medium. We observed excess [C ii] emission from the dense clumpy molecular component. It is likely to originate from molecular gas that is irradiated by an interstellar FUV-radiation field of order . Using PDR models for a spherical symmetry we find the molecular gas of L1457 consists of clumps with a density cm^-3. Their masses range between and consistent with the clump distribution derived from high resolution CO observations. [O i] 63 µm emission was not detected toward L1457.

Key words: ISM: abundances ISM: clouds ISM: individual objects: L1457 (MBM 12) 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.

Send offprint requests to: R. Timmermann
Correspondence to : timmer@ph1.uni-koeln.de

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Contents

• 1. Introduction
• 2. Observations
• 3. Origin of the [C ii] Line
  • 3.1. C⁺-cooling of the Cold Neutral Medium
  • 3.2. Excess C⁺-emission from molecular gas
  • 3.3. Dust temperature and FIR Intensity
• 4. Discussion
• Acknowledgements
• References

© European Southern Observatory (ESO) 1998

Online publication: July 27, 1998
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