Universität zu Köln

Nielbock, M., Launhardt, R., Steinacker, J., Stutz, A. M., Balog, Z., Beuther, H., Bouwman, J., Henning, Th., Hily-Blant, P., Kainulainen, J., Krause, O., Linz, H., Lippok, N., Ragan, S., Risacher, C. and Schmiedeke, A. (2012). The Earliest Phases of Star formation (EPoS) observed with Herschel: the dust temperature and density distributions of B68. Astron. Astrophys., 547. LES ULIS CEDEX A: EDP SCIENCES S A. ISSN 0004-6361

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Abstract

Context. Isolated starless cores within molecular clouds can be used as a testbed to investigate the conditions prior to the onset of fragmentation and gravitational proto-stellar collapse. Aims. We aim to determine the distribution of the dust temperature and the density of the starless core B68. Methods. In the framework of the Herschel guaranteed-time key programme The Earliest Phases of Star formation (EPoS), we have imaged B68 between 100 and 500 mu m. Ancillary data at (sub) millimetre wavelengths, spectral line maps of the (CO)-C-12 (2-1), and (CO)-C-13 (2-1) transitions, as well as an NIR extinction map were added to the analysis. We employed a ray-tracing algorithm to derive the 2D mid-plane dust temperature and volume density distribution without suffering from the line-of-sight averaging effects of simple SED fitting procedures. Additional 3D radiative transfer calculations were employed to investigate the connection between the external irradiation and the peculiar crescent-shaped morphology found in the FIR maps. Results. For the first time, we spatially resolve the dust temperature and density distribution of B68, convolved to a beam size of 36 ''.4. We find a temperature gradient dropping from (16.7(-1.0)(+1.3)) K at the edge to (8.2(-0.7)(+2.1)) K in the centre, which is about 4 K lower than the result of the simple SED fitting approach. The column density peaks at N-H = (4.3(-2.8)(+1.4)) x 10(22) cm(-2), and the central volume density was determined to n(H) = (3.4(-2.5)(+0.9)) x 10(5) cm(-3). B68 has a mass of 3.1 M-circle dot of material with A(K) > 0.2 mag for an assumed distance of 150 pc. We detect a compact source in the southeastern trunk, which is also seen in extinction and CO. At 100 and 160 mu m, we observe a crescent of enhanced emission to the south. Conclusions. The dust temperature profile of B68 agrees well with previous estimates. We find the radial density distribution from the edge of the inner plateau outward to be n(H) proportional to r(-3.5). Such a steep profile can arise from either or both of the following: external irradiation with a significant UV contribution or the fragmentation of filamentary structures. Our 3D radiative transfer model of an externally irradiated core by an anisotropic ISRF reproduces the crescent morphology seen at 100 and 160 mu m. Our CO observations show that B68 is part of a chain of globules in both space and velocity, which may indicate that it was once part of a filament that dispersed. We also resolve a new compact source in the southeastern trunk and find that it is slightly shifted in centroid velocity from B68, lending qualitative support to core collision scenarios.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Nielbock, M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Launhardt, R. UNSPECIFIED UNSPECIFIED UNSPECIFIED Steinacker, J. UNSPECIFIED UNSPECIFIED UNSPECIFIED Stutz, A. M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Balog, Z. UNSPECIFIED UNSPECIFIED UNSPECIFIED Beuther, H. UNSPECIFIED UNSPECIFIED UNSPECIFIED Bouwman, J. UNSPECIFIED UNSPECIFIED UNSPECIFIED Henning, Th. UNSPECIFIED UNSPECIFIED UNSPECIFIED Hily-Blant, P. UNSPECIFIED UNSPECIFIED UNSPECIFIED Kainulainen, J. UNSPECIFIED UNSPECIFIED UNSPECIFIED Krause, O. UNSPECIFIED UNSPECIFIED UNSPECIFIED Linz, H. UNSPECIFIED UNSPECIFIED UNSPECIFIED Lippok, N. UNSPECIFIED UNSPECIFIED UNSPECIFIED Ragan, S. UNSPECIFIED UNSPECIFIED UNSPECIFIED Risacher, C. UNSPECIFIED UNSPECIFIED UNSPECIFIED Schmiedeke, A. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-479395
DOI:	10.1051/0004-6361/201219139
Journal or Publication Title:	Astron. Astrophys.
Volume:	547
Date:	2012
Publisher:	EDP SCIENCES S A
Place of Publication:	LES ULIS CEDEX A
ISSN:	0004-6361
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language SPITZER-SPACE-TELESCOPE; MOLECULAR CLOUD CORES; MULTIBAND IMAGING PHOTOMETER; CONTINUUM RADIATIVE-TRANSFER; SOUTHERN BOK GLOBULES; INFRARED-DARK CLOUD; LOW-MASS PROTOSTARS; PRESTELLAR CORES; INITIAL CONDITIONS; EXTINCTION LAW Multiple languages Astronomy & Astrophysics Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/47939