APEX-CHAMP+ high-J CO observations of low-mass young stellar objects - II. Distribution and origin of warm molecular gasT. A. van Kempen, E. F. van Dishoeck, R. Güsten, L. E. Kristensen, P. Schilke, M. R. Hogerheijde, W. Boland, K. M. Menten and F. WyrowskiA&A, 507 3 (2009) 1425-1442DOI: https://doi.org/10.1051/0004-6361/200912507