Search for Low-Mass Exoplanets by Gravitational Microlensing at High Magnification

F. Abe,¹ D. P. Bennett,² I. A. Bond,³ S. Eguchi,¹ Y. Furuta,¹ J. B. Hearnshaw,⁴ K. Kamiya,¹ P. M. Kilmartin,⁴ Y. Kurata,¹ K. Masuda,¹ Y. Matsubara,¹ Y. Muraki,¹ S. Noda,⁵ K. Okajima,¹ A. Rakich,⁶ N. J. Rattenbury,^7* T. Sako,¹ T. Sekiguchi,¹ D. J. Sullivan,⁸ T. Sumi,⁹ P. J. Tristram,¹⁰ T. Yanagisawa,¹¹ P. C. M. Yock,¹⁰ A. Gal-Yam,^12,13 Y. Lipkin,¹⁴ D. Maoz,¹⁴ E. O. Ofek,¹⁴ A. Udalski,¹⁵ O. Szewczyk,¹⁵ K. ebru,¹⁵ I. Soszyski,¹⁵ M. K. Szymaski,¹⁵ M. Kubiak,¹⁵ G. Pietrzyski,^15,16 L. Wyrzykowski¹⁵

Observations of the gravitational microlensing event MOA 2003-BLG-32/OGLE 2003-BLG-219 are presented, for which the peak magnification was over 500, the highest yet reported. Continuous observations around the peak enabled a sensitive search for planets orbiting the lens star. No planets were detected. Planets 1.3 times heavier than Earth were excluded from more than 50% of the projected annular region from approximately 2.3 to 3.6 astronomical units surrounding the lens star, Uranus-mass planets were excluded from 0.9 to 8.7 astronomical units, and planets 1.3 times heavier than Saturn were excluded from 0.2 to 60 astronomical units. These are the largest regions of sensitivity yet achieved in searches for extrasolar planets orbiting any star.

¹ Solar Terrestrial Environment Laboratory, Nagoya University, Nagoya 464-01, Japan.
² Department of Physics, Notre Dame University, Notre Dame IN 46556, USA.
³ Institute of Information and Mathematical Sciences, Massey University at Albany, Auckland, New Zealand.
⁴ Department of Physics and Astronomy, University of Canterbury, Christchurch, New Zealand.
⁵ National Astronomical Observatory, Tokyo, Japan.
⁶ Electro Optics Systems, Canberra, Australia.
⁷ Department of Physics and Astronomy, University of Manchester, Manchester, UK.
⁸ School of Chemical and Physical Sciences, Victoria University, Wellington, New Zealand.
⁹ Department of Astrophysical Sciences, Princeton University, Princeton NJ 08544, USA.
¹⁰ Department of Physics, University of Auckland, Auckland, New Zealand.
¹¹ National Aerospace Laboratory, Tokyo, Japan.
¹² Department of Astronomy, California Institute of Technology, Pasadena, CA 91025, USA.
¹³ Hubble Fellow.
¹⁴ School of Physics and Astronomy, Raymond and Beverley Sackler Faculty of Exact Sciences, Tel-Aviv University, Tel Aviv 69978, Israel.
¹⁵ Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa, Poland.
¹⁶ Universidad de Concepcion, Departamento de Fisica, Casilla 160-C, Concepcion, Chile.

^* To whom correspondence should be addressed. E-mail: njr{at}jb.man.ac.uk

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