1. Department of Physics & Astronomy, University of Denver, 2112 E Wesley Ave., 80208, Denver, USA
2. Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK
3. Department of Astronomy & Astrophysics, University of Toronto, 50 St. George Street, M5S 3H4, Toronto, Canada
4. Department of Physics & Astronomy, East Tennessee State University, Johnson City, TN 37614, USA