Letters to the Editor
F. Fontani1,2, A. Palau3, P. Caselli4, Á. Sánchez-Monge5, M. J. Butler6, J. C. Tan6,7, I. Jiménez-Serra8, G. Busquet5,9, S. Leurini10 and M. Audard11,12
ESO, Karl Schwarzschild Str. 2, 85748 Garching bei Munchen, Germany
2 Institut de Radio-Astronomie Millimétrique, 300 rue de la Piscine, 38406 Saint Martin d’Hères, France
3 Institut de Ciències de l’Espai (CSIC-IEEC), Campus UAB-Facultat de Ciències, Torre C5-parell 2, 08193 Bellaterra, Spain
4 School of Physics and Astronomy, E.C. Stoner Building, University of Leeds, Leeds LS2 9JT, UK
5 Departament d’Astronomia i Meteorologia (IEEC-UB), Institut de Ciències del Cosmos, Universitat de Barcelona, Martí i Franquès, 1, 08028 Barcelona, Spain
6 Department of Astronomy, University of Florida, Gainesville, FL 32611, USA
7 Department of Physics, University of Florida, Gainesville, FL 32611, USA
8 Harvard-Smithonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA
9 INAF-Istituto di Fisica dello Spazio Interplanetario, Via Fosso del Cavaliere 100, 00133 Roma, Italy
10 Max-Planck-Institut fur Radioastronomie, Auf dem Hugel 69, 53121 Bonn, Germany
11 ISDC Data Center for Astrophysics, University of Geneva, Ch. d’Ecogia 16, 1290 Versoix, Switzerland
12 Geneva Observatory, University of Geneva, Ch. des Maillettes 51, 1290 Versoix, Switzerland
Received: 2 February 2011
Accepted: 25 March 2011
Context. Theory predicts, and observations confirm, that the column density ratio of a molecule containing D to its counterpart containing H can be used as an evolutionary tracer in the low-mass star formation process.
Aims. Since it remains unclear if the high-mass star formation process is a scaled-up version of the low-mass one, we investigated whether the relation between deuteration and evolution can be applied to the high-mass regime.
Methods. With the IRAM-30 m telescope, we observed rotational transitions of N2D+ and N2H+ and derived the deuterated fraction in 27 cores within massive star-forming regions understood to represent different evolutionary stages of the massive-star formation process.
Results. The abundance of N2D+ is higher at the pre-stellar/cluster stage, then drops during the formation of the protostellar object(s) as in the low-mass regime, remaining relatively constant during the ultra-compact HII region phase. The objects with the highest fractional abundance of N2D+ are starless cores with properties very similar to typical pre-stellar cores of lower mass. The abundance of N2D+ is lower in objects with higher gas temperatures as in the low-mass case but does not seem to depend on gas turbulence.
Conclusions. Our results indicate that the N2D+-to-N2H+ column density ratio can be used as an evolutionary indicator in both low- and high-mass star formation, and that the physical conditions influencing the abundance of deuterated species likely evolve similarly during the processes that lead to the formation of both low- and high-mass stars.
Key words: stars: formation / ISM: clouds / ISM: molecules / radio lines: ISM
Based on observations carried out with the IRAM 30 m telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).
Appendices are available in electronic form at http://www.aanda.org
© ESO, 2011