Letters to the Editor

SiO outflows in high-mass star forming regions: A potential chemical clock?^⋆,⋆⋆

¹ INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
e-mail: sepulcre@arcetri.astro.it
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

Abstract

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 L_bol/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.