SiO outflows in high-mass star forming regions: A potential chemical clock? A. López-Sepulcre, C. M. Walmsley, R. Cesaroni, C. Codella, F. Schuller, L. Bronfman, S. J. Carey, K. M. Menten, S. Molinari and A. Noriega-Crespo A&A, 526 (2011) L2 Published online: 13 December 2010 DOI: 10.1051/0004-6361/201015827