[1] New Mexico State Univ, Dept Astron, Dept 4500, Las Cruces, NM 88003 USA
[2] Univ Nacl Autonoma Mexico, Astron Inst, Morelia 58090, Michoacan, Mexico
[3] CALTECH, Jet Prop Lab, Pasadena, CA 91109 USA
[4] Australian Natl Univ, Mt Stromlo & Siding Spring Observ, Weston Creek, ACT 2611, Australia
[5] Univ Michigan, Dept Atmospher Ocean & Space Sci, Ann Arbor, MI 48109 USA
[6] Space Telescope Sci Inst, Baltimore, MD 21218 USA
[7] European Space Agcy, Div Astrophys, Dept Space Sci, F-75738 Paris 15, France
[8] Univ Wisconsin, Dept Astron, Madison, WI 53706 USA
[9] Carnegie Mellon Univ, Dept Phys, Pittsburgh, PA 15213 USA
[10] Arizona State Univ, Dept Phys & Astron, Tempe, AZ 85287 USA
[11] CALTECH, Dept Geol & Planetary Sci, Pasadena, CA 91125 USA