Letters to the Editor

Deuteration as an evolutionary tracer in massive-star formation^⋆,⋆⋆

¹ 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
e-mail: fontani@iram.fr
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

Abstract

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.