EDP Sciences Journals List
Advanced Search
Subscriber Authentication Point
Home All issues Volume 489/1 Article
Free access article

Issue A&A
Volume 489, Number 1, October I 2008
Page(s) 207 - 216
Section Interstellar and circumstellar matter
DOI http://dx.doi.org/10.1051/0004-6361:20078431
Published online 23 July 2008



A&A 489, 207-216 (2008)
DOI: 10.1051/0004-6361:20078431

The photon dominated region in the IC 348 molecular cloud

K. Sun1, V. Ossenkopf1, 2, C. Kramer1, B. Mookerjea3, M. Röllig4, M. Cubick1, and J. Stutzki1

1  I. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany
    e-mail: kefeng@ph1.uni-koeln.de
2  SRON Netherlands Institut for Space Research, PO Box 800, 9700 AV Groningen, The Netherlands
3  Department of Astronomy & Astrophysics, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005, India
4  Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany

Received 7 August 2007 / Accepted 17 July 2008

Abstract
Aims. In this paper we discuss the physical conditions of clumpy nature in the IC 348 molecular cloud. We show that the millimeter and sub-millimeter line emission from the IC 348 molecular cloud can be modelled as originating from a photon dominated region (PDR).
Methods. We combine new observations of fully sampled maps in [C I] at 492 GHz and 12CO 4–3, taken with the KOSMA 3 m telescope at about 1´ resolution, with FCRAO data of 12CO 1–0, 13CO 1–0 and far-infrared continuum data observed by HIRES/IRAS. To derive the physical parameters of the region we analyze the line ratios of [C I] 3P1–3P 0/12CO 4–3, [C I]3P1–3P 0/13CO 1–0, and 12CO 4–3/12CO 1–0. A first rough estimate of abundance is obtained from an LTE analysis. To understand the [C I] and CO emission from the PDRs in IC 348, we use a clumpy PDR model. With an ensemble of identical clumps, we constrain the total mass from the observed absolute intensities. Then we apply a more realistic clump distribution model with a power law index of 1.8 for clump-mass spectrum and a power law index of 2.3 for mass-size relation.
Results. We provide detailed fits to observations at seven representative positions in the cloud, revealing clump densities between 4 $\times$ 104 cm-3 and 4 $\times$ 105 cm-3 and C/CO column density ratios between 0.02 and 0.26. The derived FUV flux from the model fit is consistent with the field calculated from FIR continuum data, varying between 2 and 100 Draine units across the cloud. We find that both an ensemble of identical clumps and an ensemble with a power law clump mass distribution produce line intensities which are in good agreement (within a factor ~ 2) with the observed intensities. The models confirm the anti-correlation between the C/CO abundance ratio and the hydrogen column density found in many regions.


Key words: ISM: clouds -- ISM: dust, extinction -- ISM: structure -- ISM: individual objects: IC 348



© ESO 2008


What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.
  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.