A timeline for massive star-forming regions via combined observation of o-H2D+ and N2D+ A. Giannetti, S. Bovino, P. Caselli, S. Leurini, D. R. G. Schleicher, B. Körtgen, K. M. Menten, T. Pillai and F. Wyrowski A&A, 621 (2019) L7 Published online: 09 January 2019 DOI: 10.1051/0004-6361/201834602