1. Department of Physics and Astronomy, Texas A&M University , 4242 TAMU, College Station, TX 77843 USA
2. Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology , Cambridge, MA 02139, USA
3. Johns Hopkins APL , 11100 Johns Hopkins Rd, Laurel, MD 20723, USA
4. Department of Physics and Astronomy, University of Victoria , Victoria, BC V8W 2Y2, Canada
5. Department of Astronomy, University of Texas at Austin , Austin, TX 78712, USA
6. Department of Astronomy, University of Wisconsin-Madison , 475 N. Charter St., Madison, WI 53703, USA
7. Department of Astronomy, Stockholm University , Stockholm, SE-10691, Sweden