1. Université de Strasbourg, CNRS, Observatoire Astronomique de Strasbourg, UMR 7550, F-67000 Strasbourg, France
2. Institut d’optique Graduate School, 91120 Palaiseau, France
3. SOFIA Science Center, NASA Ames Research Center, Moffett Field, CA 94035, USA
4. Department of Astronomy, University of Wisconsin-Madison, Madison, WI 53706, USA