The detached dust shells around the carbon AGB stars R Sculptoris and V644 Scorpii M. Maercker, S. Ramstedt, M. L. Leal-Ferreira, G. Olofsson and H. G. Floren A&A, 570 (2014) A101 Published online: 30 October 2014 DOI: 10.1051/0004-6361/201424892