1. I. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, D-50923 Köln, Germany
2. Department of Physics, Aristotle University of Thessaloniki, GR-54124 Thessaloniki, Greece
3. Department of Space, Earth and Environment, Chalmers University of Technology, SE-412 93 Gothenburg, Sweden
4. Department of Astronomy, University of Virginia, Charlottesville, VA 22904, USA
5. Center for Astrophysics and Space Astronomy, Department of Astrophysical and Planetary Sciences, University of Colorado Boulder, Boulder, CO 80309, USA
6. ALMA Project, National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588, Japan