Astron. Astrophys. 361, 555-580 (2000)

An ISOCAM absorption survey of the structure of pre-stellar cloud cores ^*

A. Bacmann  ^{**  1}, P. André  ^{***  1}, J.-L. Puget ², A. Abergel ², S. Bontemps ³ and D. Ward-Thompson <sup>4

1</sup> CEA, DSM, DAPNIA, Service d'Astrophysique, C.E. Saclay, 91191 Gif-sur-Yvette Cedex, France
² Institut d'Astrophysique Spatiale, Orsay, France
³ Observatoire de Bordeaux, Floirac, France
⁴ Department of Physics & Astronomy, Cardiff University, P.O. Box 913, Cardiff, UK

Received 27 October 1999 / Accepted 7 March 2000

Abstract

We present the results of a mid-infrared ( 7 µm) imaging survey of a sample of 24 starless dense cores carried out at an angular resolution of 6" with the ISOCAM camera aboard the Infrared Space Observatory (ISO). The targeted cores are believed to be pre-stellar in nature and to represent the initial conditions of low-mass, isolated star formation. In previous submillimeter dust continuum studies of such pre-stellar cores, it was found that the derived column density profiles did not follow a single power-law such as throughout their full extent but flattened out near their centre. These submillimeter observations however could not constrain the density profiles at radii greater than 10000 AU. The present absorption study uses ISOCAM's sensitivity to map these pre-stellar cores in absorption against the diffuse mid-infrared background. The goal was to determine their structure at radii that extend beyond the limits of sensitivity of the submillimeter continuum maps and at twice as good an angular resolution. Among the 24 cores observed in our survey, a majority of them show deep absorption features. The starless cores studied here all show a column density profile that flattens in the centre, which confirms the submillimeter emission results. Moreover, beyond a radius of AU, the typical column density profile steepens with distance from core centre and gets steeper than , until it eventually merges with the low-density ambient molecular cloud. At least three of the cores present sharp edges at  AU and appear to be decoupled from their parent clouds, providing finite reservoirs of mass for subsequent star formation.

Key words: stars: flare ISM: clouds ISM: dust, extinction ISM: structure

* 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: Astrophysikalisches Institut und Universitäts Sternwarte, Schillergässchen 2-3, 07745 Jena, Germany (bacmann@astro.uni-jena.de)
*** pandre@cea.fr

Send offprint requests to: A. Bacmann

SIMBAD Objects

Contents

• 1. Introduction
• 2. Observations and data reduction
  • 2.1. Starless core sample
  • 2.2. ISOCAM observations
    • 2.2.1. Observational parameters
    • 2.2.2. Data reduction
    • 2.2.3. Noise estimation
  • 2.3. Millimeter observations
• 3. Results and analysis
  • 3.1. ISOCAM images
  • 3.2. Comparison with the millimeter continuum maps
  • 3.3. Modelling of the mid-infrared absorption
    • 3.3.1. Central column density from millimeter continuum data
    • 3.3.2. Outer column density from millimeter line data
    • 3.3.3. Estimates of the background and foreground intensities
  • 3.4. Radial column density profiles
    • 3.4.1. Derivation of the profiles
    • 3.4.2. Results
  • 3.5. Uncertainties, difficulties, limitations
    • 3.5.1. Dust extinction curve in the mid-IR
    • 3.5.2. Simulations of non uniform background and foreground intensities
• 4. Discussion: comparison with theoretical models of core structure
  • 4.1. Comparison with simple parameterized spherical models
  • 4.2. Comparison with logotropic spheres
  • 4.3. Comparison with self-similar, singular models
  • 4.4. Comparison with magnetic ambipolar diffusion models of cloud cores
  • 4.5. Filamentary structures and cloud fragmentation
  • 4.6. Implications for the earliest stages of collapse
• 5. Summary and conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: October 2, 2000
helpdesk@link.springer.de