Mass measurement of a single unseen star and planetary detection efficiency for OGLE 2007-BLG-050^{*,**,***,****}

¹ Institut d'Astrophysique de Paris, INSU-CNRS, 98 bis Boulevard Arago, 75014 Paris, France e-mail: [batista;beaulieu;marquett]@iap.fr
² Department of Astronomy, Ohio State University, 140 W. 18th Ave., Columbus, OH 43210, USA e-mail: [dong;gould;gaudi]@astronomy.ohio-state.edu
³ Astronomisches Rechen-Institut, Zentrum für Astronomie, Heidelberg University, Mönchhofstr. 12–14, 69120 Heidelberg, Germany
⁴ Auckland Observatory, Auckland, New Zealand e-mail: gwchristie@christie.org.nz
⁵ Program of Brain Korea, Department of Physics, Chungbuk National University, 410 Seongbong-Rho, Hungduk-Gu, Chongju 371-763, Korea e-mail: cheongho@astroph.chungbuk.ac.kr
⁶ Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa, Poland e-mail: [udalski;mj;msz;mk;pietrzyn;soszynsk; kulaczyk]@astrouw.edu.pl
⁷ Bronberg Observatory, Centre for Backyard Astrophysics Pretoria, South Africa e-mail: lagmonar@nmsa.org
⁸ Benoziyo Center for Astrophysics, Weizmann Institute of Science, 76100 Rehovot, Israel e-mail: avishay.gal-yam@weizmann.ac.il
⁹ Institute of Astronomy, Cambridge University, Madingley Rd., Cambridge, CB 0HA, UK e-mail: bjohnson@ast.cam.ac.uk
¹⁰ Wise Observatory, Tel Aviv University, 69978 Tel Aviv, Israel e-mail: [dani;shai;david;shporer]@wise.tau.ac.il
¹¹ Korea Astronomy and Space Science Institute, 61-1 Hwaam-Dong, Yuseong-Gu, Daejeon 305-348, Korea e-mail: bgpark@kasi.re.kr
¹² Farm Cove Observatory, Centre for Backyard Astrophysics, Pakuranga, Auckland New Zealand e-mail: farmcoveobs@xtra.co.nz
¹³ Department of Astronomy, Columbia University, Pupin Physics Laboratories, New York, NY 10027, USA e-mail: mcgreer@astro.columbia.edu
¹⁴ AUT University, Auckland, New Zealand e-mail: tim.natush@aut.ac.nz
¹⁵ Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, CA 91125, USA e-mail: eran@astro.caltech.edu
¹⁶ University of Canterbury, Department of Physics & Astronomy, Private Bag 4800, Christchurch, New Zealand
¹⁷ University of Notre Dame, Department of Physics, 225 Nieuwland Science Hall, Notre Dame, IN 46556, USA e-mail: bennett@nd.edu
¹⁸ European Southern Observatory, Casilla 19001, Vitacura 19, Santiago, Chile
¹⁹ Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead CH41 1LD, UK
²⁰ Isaac Newton Group, Apartado de Correos 321, 38700 Santa Cruz de La Palma, Spain
²¹ SOFIA Science Center, Mail stop N211-3, Moffett Field CA 94035, USA
²² McDonald Observatory, 16120 St Hwy Spur 78, Fort Davis, TX 79734, USA
²³ Dept. of Physics/Boyden Observatory, University of the Free State, Bloemfontein 9300, South Africa
²⁴ University of Tasmania, School of Maths and Physics, Private bag 37, GPO Hobart, Tasmania 7001, Australia
²⁵ Lawrence Livermore National Laboratory, IGPP, PO Box 808, Livermore, CA 94551, USA
²⁶ DSM/DAPNIA, CEA Saclay, 91191 Gif-sur-Yvette cedex, France
²⁷ SUPA, University of St Andrews, School of Physics & Astronomy, North Haugh, St Andrews, KY16 9SS, UK
²⁸ Physics department, Faculty of Arts and Sciences, University of Rijeka, 51000 Rijeka, Croatia
²⁹ Technical University of Vienna, Dept. of Computing, Wiedner Hauptstrasse 10, Vienna, Austria
³⁰ Observatoire Midi-Pyrénées, UMR 5572, 14 avenue Edouard Belin, 31400 Toulouse, France
³¹ Niels Bohr Institute, Astronomical Observatory, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
³² NASA Exoplanet Science Institute, Caltech, MS 100-22, 770 South Wilson Avenue Pasadena, CA 91125, USA
³³ Perth Observatory, Walnut Road, Bickley, Perth 6076, Australia
³⁴ South African Astronomical Observatory, PO Box 9 Observatory 7935, South Africa
³⁵ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
³⁶ Astronomy Unit, School of Mathematical Sciences, Queen Mary, University of London, Mile End Road, London E1 4NS, UK
³⁷ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK e-mail: wyrzykow@ast.cam.ac.uk
³⁸ Universidad de Concepción, Departamento de Fisica, Casilla 160–C, Concepción, Chile e-mail: szewczyk@astro-udec.cl
³⁹ Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya, 464-8601, Japan
⁴⁰ Institute for Information and Mathematical Sciences, Massey University, Private Bag 102-904, Auckland 1330, New Zealand
⁴¹ Computer Science Department, University of Auckland, Auckland, New Zealand
⁴² Mt. John Observatory, PO Box 56, Lake Tekapo 8770, New Zealand
⁴³ Department of Physics, Konan University, Nishiokamoto 8-9-1, Kobe 658-8501, Japan
⁴⁴ Nagano National College of Technology, Nagano 381-8550, Japan
⁴⁵ Department of Physics, University of Auckland, Private Bag 92-019, Auckland 1001, New Zealand
⁴⁶ Tokyo Metropolitan College of Industrial Technology, Tokyo 116-8523, Japan
⁴⁷ School of Chemical and Physical Sciences, Victoria University, Wellington, New Zealand

Received: 17 July 2009
Accepted: 17 September 2009

Abstract

Aims. We analyze OGLE-2007-BLG-050, a high magnification microlensing event () whose peak occurred on 2 May, 2007, with pronounced finite-source and parallax effects. We compute planet detection efficiencies for this event in order to determine its sensitivity to the presence of planets around the lens star.

Methods. Both finite-source and parallax effects permit a measurement of the angular Einstein radius  mas and the parallax , leading to an estimate of the lens mass and its distance to the observer  kpc. This is only the second determination of a reasonably precise (<) mass estimate for an isolated unseen object, using any method. This allows us to calculate the planetary detection efficiency in physical units , where is the projected planet-star separation and m_p is the planet mass.

Results. When computing planet detection efficiency, we did not find any planetary signature, i.e. none of the planetary configurations provides a improvement higher than 60, and our detection efficiency results reveal significant sensitivity to Neptune-mass planets, and to a lesser extent Earth-mass planets in some configurations. Indeed, Jupiter and Neptune-mass planets are excluded with a high confidence for a large projected separation range between the planet and the lens star, respectively [0.6–10] and [1.4–4] AU, and Earth-mass planets are excluded with a 10% confidence in the lensing zone, i.e. [1.8–3.1] AU.