Chemical and physical small-scale structure in a pre-stellar core

¹ Institut für integrierte Naturwissenschaften, Abteilung Physik, Universität Koblenz-Landau, Universitätsstr. 1, 56070 Koblenz, Germany e-mail: heithausen@uni-koblenz.de
² Radioastronomisches Institut, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany e-mail: christoph-boettner@gmx.de
³ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany e-mail: walter@mpia-hd.mpg.de

Received: 27 August 2007
Accepted: 9 June 2008

Abstract

Aims. We present a comparative study of several molecular lines and of the dust contiunuum at 1.2mm in a pre-stellar core that is embedded in the Galactic cirrus cloud MCLD123.5+24.9. Previous studies found that the core is gravitationally stable and shows signs of inward motion.

Methods. Using the Owens Valley (OVRO) and Plateau de Bure (PdB) interferometers we obtained high-angular resolution maps of the core in the carbon monosulfide CS (21) and the cyanoacetylene HC₃N (109) transitions. Together with CS (54), C³⁴S (32), and bolometer data obtained with the IRAM 30 m telescope, we analyse the excitation conditions and the structural properties of the cloud.

Results. On the one hand, the new CS (J = 21) observations reveal significant substructure on a scale of about , i.e., the beam size, corresponding to about 1050 AU at an adopted distance of 150 pc. On the other hand, the interferometric observations in the HC₃N (J = 109) transition shows just one single well resolved clump in the inner part of the core. This core is well described by an intensity profile following from a centrally peaked volume density distribution. We find no evidence for depletion of CS onto dust grains. The inward motion seen in the CS (21) occurs one-sided from the middle of the filamentary cloud towards the HC₃N core.