[1] Catholic Univ Amer, Dept Phys, Washington, DC 20064 USA
[2] George Mason Univ, Dept Phys & Astron, Fairfax, VA 22030 USA
[3] NASA, Goddard Space Flight Ctr, Code 671, Greenbelt, MD 20771 USA
[4] Univ Hawaii Manoa, Inst Astron, Coll Nat Sci, Pukalani, HI USA