[1] Carnegie Inst Washington Observ, Pasadena, CA 91101 USA
[2] Carnegie Mellon Univ, Dept Phys, Pittsburgh, PA 15213 USA
[3] NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA
[4] Nagoya Univ, Dept Astrophys, Nagoya, Aichi 46401, Japan
[5] Space Telescope Sci Inst, Baltimore, MD 21218 USA