Volume 577, May 2015
|Number of page(s)||15|
|Section||Interstellar and circumstellar matter|
|Published online||06 May 2015|
1 Department of Physics, PO Box 64, 00014 University of Helsinki, Finland
2 Institut d’Astrophysique Spatiale, Université Paris Sud, 91405 Orsay Cedex, France
3 Finnish Centre for Astronomy with ESO (FINCA), University of Turku, Väisäläntie 20, 21500 Piikkiö, Finland
Received: 15 January 2014
Accepted: 5 February 2015
Context. The study of prestellar cores is essential to understanding the initial stages of star formation. With Herschel more cold clumps have been detected than ever before. For this study we have selected 21 cold clumps from 20 Herschel fields observed as a follow-up on original Planck detections. We have observed these clumps in 13CO (1−0), C18O (1−0), and N2H+ (1−0) lines.
Aims. Our aim is to find out if these cold clumps are prestellar. We have examined to what extent independent analysis of the dust and the molecular lines lead to similar conclusions about the masses of these objects.
Methods. We calculate the clump masses and densities from the dust continuum and molecular line observations and compare these to each other and to the virial and Bonnor-Ebert masses calculated for each clump. Finally we examine two of the fields with radiative transfer models to estimate CO abundances.
Results. When excitation temperatures could be estimated, the column densities derived from molecular line observations were comparable to those from dust continuum data. The median column density estimates are 4.2 × 1021 cm-2 and 5.5 × 1021 cm-2 for the line and dust emission data, respectively. The calculated abundances, column densities, volume densities, and masses all have large uncertainties and one must be careful when drawing conclusions. Abundance of 13CO was found in modeling the two clumps in the field G131.65+9.75 to be close to the usual value of 10-6. The abundance ratio of 13CO and C18O was ~10. Molecular abundances could only be estimated with modeling, relying on dust column density data.
Conclusions. The results indicate that most cold clumps, even those with dust color temperatures close to 11 K, are not necessarily prestellar.
Key words: ISM: clouds / submillimeter: ISM / molecular data
Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
Appendices are available in electronic form at http://www.aanda.org
© ESO, 2015
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.