1. Department of Physics and Astronomy, and Bartol Research Institute, University of Delaware, Newark, DE 19716, USA
2. Department of Physics and Astronomy, Howard University, Washington, DC 20059, USA
3. Center for Research and Exploration in Space Science and Technology, and X-ray Astrophysics Laboratory, NASA/GSFC, Greenbelt, MD 20771, USA
4. Institute of Astronomy, KU Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium
5. LESIA, Paris Observatory, PSL University, CNRS, Sorbonne University, Université de Paris, 5 place Jules Janssen, F-92195 Meudon, France
6. American Association of Variable Star Observers, 49 Bay State Rd., Cambridge, MA 02138, USA
7. Department of Physics and Astronomy, Bishop’s University, Sherbrooke, QC J1M 1Z7, Canada
8. Penn State Scranton, 120 Ridge View Drive, Dunmore, PA 18512, USA
9. Department of Physics and Space Physics, Royal Military College of Canada, PO Box 17000, Kingston, ON K7K 7B4, Canada