Letters to the Editor
INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125
2 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
3 Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
4 Spitzer Science Center, California Institute of Technology, Mail Code 220-6, Pasadena, CA 91125, USA
5 INAF – Istituto Fisica Spazio Interplanetario, V. Fosso del Cavaliere 100, 00133 Roma, Italy
Received: 27 September 2010
Accepted: 19 November 2010
Context. Some theoretical models propose that O-B stars form via accretion, in a similar fashion to low-mass stars. Jet-driven molecular outflows play an important role in this scenario, and their study can help to understand the process of high-mass star formation and the different evolutionary phases involved.
Aims. Observations towards low-mass protostars so far favour an evolutionary picture in which jets are always associated with Class 0 objects while more evolved Class I/II objects show less evidence of powerful jets. The present study aims at checking whether an analogous picture can be found in the high-mass case.
Methods. The IRAM 30-m telescope (Spain) has been used to perform single-pointing SiO(2–1) and (3–2) observations towards a sample of 57 high-mass molecular clumps in different evolutionary stages. Continuum data at different wavelengths, from mid-IR to 1.2 mm, have been gathered to build the spectral energy distributions of all the clumps and estimate their bolometric luminosities.
Results. SiO emission at high velocities, characteristic of molecular jets, is detected in 88% of our sources, a very high detection rate indicating that there is ongoing star formation activity in most of the sources of our sample. The SiO(2–1) luminosity drops with Lbol/M, which suggests that jet activity declines as time evolves. This represents the first clear evidence of a decrease of SiO outflow luminosity with time in a homogeneous sample of high-mass molecular clumps in different evolutionary stages. The SiO(3–2) to SiO(2–1) integrated intensity ratio shows only minor changes with evolutionary state.
Key words: stars: formation / ISM: clouds / ISM: jets and outflows / ISM: molecules
Based on observations conducted with the IRAM 30-m telescope near Pico Veleta (Granada, Spain), and the Atacama Pathfinder Experiment (APEX) ESO project: 181.C-0885.. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain). APEX is a collaboration between the Max-Planck-Institut für Radioastronomie, the European Southern Observatory, and the Onsala Space Observatory.
Appendices are only available in electronic form at http://www.aanda.org
© ESO, 2010