1. Lowell Observatory; 1400 West Mars Hill Road Flagstaff Arizona 86001 USA
2. Department of Physics; University of Helsinki; P.O. Box 64 Helsinki FI-00014 Finland
3. Institute Astronomical Observatory; Faculty of Physics; Adam Mickiewicz University; Słoneczna 36 Poznań 60-286 Poland
4. Finnish Geodetic Institute; P.O. Box 15 Masala FI-02431 Finland
5. Department of Physics and Astronomy; Northern Arizona University; P.O. Box 6010 Flagstaff Arizona 86011 USA