Gravitationally bound cores in a molecular cirrus cloud

¹ Radioastronomisches Institut der Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
² Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
³ I. Physikalisches Institut der Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
⁴ Harvard-Smithonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA

Corresponding author: A. Heithausen, heith@astro.uni-bonn.de

Received: 23 November 2001
Accepted: 18 December 2001

Abstract

Using MAMBO at the IRAM 30 m telescope we have observed a dense core in the cirrus cloud MCLD 123.5+24.9 in the dust continuum emission at 250 GHz. The core is detected as an elongated filament with an extent of , corresponding to 0.18 pc0.03 pc at an adopted distance of 150 pc. We find a close correlation between the continuum emission and previously observed C¹⁸O (10) line emission. Using standard dust models we derive hydrogen column densities of up to 10²² cm^-2. The total mass for the filament is about 0.66 . We also present observations of the HC₃N (32), (43), and (109) emission lines obtained with the MPIfR 100 m and the IRAM 30 m telescopes. The distribution is very different from the dust continuum and the C¹⁸O (10) line emission. HC₃N is concentrated in two distinct clumps located at the ends of the filament seen in the other tracers. Based on a LVG analysis of the HC₃N transitions we derive column densities of cm^-2/kms^-1 and volume densities of  cm^-3. We find that the HC₃N clumps have masses of 0.13 and 0.19 . Our data demonstrate that the cirrus cloud cores are gravitationally bound, and that they show chemical structure indicating different evolutionary stages within the cloud.