The Temperatures of Red Supergiants: how cool are the coolest massive stars? B. Davies, R.-P. Kudritzki, B. Plez, M. Bergemann, A. Lançon, S. Trager, Z. Gazak, C. Evans and A. Chiavassa EAS Publications Series, 60 (2013) 69-76 Published online: 23 May 2013 DOI: 10.1051/eas/1360007