Статья

Microlensing Optical Depth toward the Galactic Bulge from Microlensing Observations in Astrophysics Group Observations during 2000 with Difference Image Analysis

T. SumiPrinceton University Observatory, Princeton, NJ 08544-1001F. AbeSolar-Terrestrial Environment Laboratory, Nagoya University, Nagoya 464-8601, JapanI. A. BondInstitute of Astronomy, University of Edinburgh, Royal Observatory, Edinburgh, UKR. J. DoddCarter National Observatory, Wellington, New ZealandJ. B. HearnshawDepartment of Physics and Astronomy, University of Canterbury, Christchurch, New ZealandMitsuhiko HondaInstitute of Cosmic Ray Research, University of Tokyo, Chiba 277-0882, JapanMareki HonmaNational Astronomical Observatory, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, JapanYukitoshi Kan‐yaNational Astronomical Observatory, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, JapanP. M. KilmartinDepartment of Physics and Astronomy, University of Canterbury, Christchurch, New ZealandK. MasudaSolar-Terrestrial Environment Laboratory, Nagoya University, Nagoya 464-8601, JapanY. MatsubaraSolar-Terrestrial Environment Laboratory, Nagoya University, Nagoya 464-8601, JapanY. MurakiSolar-Terrestrial Environment Laboratory, Nagoya University, Nagoya 464-8601, JapanT. NakamuraDepartment of Physics, Kyoto University, Kyoto 606-8502, JapanRyosuke NishiDepartment of Physics, Niigata University, Niigata 950-2181, JapanS. NodaNational Astronomical Observatory, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, JapanKei OhnishiNagano National College of Technology, Nagano, JapanO. K. L. PettersonDepartment of Physics and Astronomy, University of Canterbury, Christchurch, New ZealandNicholas J. RattenburyDepartment of Physics, University of Auckland, Auckland, New ZealandM. ReidSchool of Chemical and Physical Sciences, Victoria University, Wellington, New ZealandTo. SaitoY. SaitoSolar-Terrestrial Environment Laboratory, Nagoya University, Nagoya 464-8601, JapanH. SatoM. SekiguchiInstitute of Cosmic Ray Research, University of Tokyo, Chiba 277-0882, JapanJ. SkuljanDepartment of Physics and Astronomy, University of Canterbury, Christchurch, New ZealandD. J. SullivanM. TakeutiAstronomical Institute, Tohoku University, Sendai 980-8578, JapanP. J. TristramDepartment of Physics and Astronomy, University of Canterbury, Christchurch, New ZealandS. WilkinsonTatsuya YanagisawaP. C. M. YockDepartment of Physics, University of Auckland, Auckland, New Zealand

2003en

ABI

Аннотация

We analyze the data of the gravitational microlensing survey carried out by by the MOA group during 2000 towards the Galactic Bulge (GB). Our observations are designed to detect efficiently high magnification events with faint source stars and short timescale events, by increasing the the sampling rate up to 6 times per night and using Difference Image Analysis (DIA). We detect 28 microlensing candidates in 12 GB fields corresponding to 16 deg^2. We use Monte Carlo simulations to estimate our microlensing event detection efficiency, where we construct the I-band extinction map of our GB fields in order to find dereddened magnitudes. We find a systematic bias and large uncertainty in the measured value of the timescale $t_{\rm Eout}$ in our simulations. They are associated with blending and unresolved sources, and are allowed for in our measurements. We compute an optical depth tau = 2.59_{-0.64}^{+0.84} \times 10^{-6} towards the GB for events with timescales 0.3<t_E<200 days. We consider disk-disk lensing, and obtain an optical depth tau_{bulge} = 3.36_{-0.81}^{+1.11} \times 10^{-6}[0.77/(1-f_{disk})] for the bulge component assuming a 23% stellar contribution from disk stars. These observed optical depths are consistent with previous measurements by the MACHO and OGLE groups, and still higher than those predicted by existing Galactic models. We present the timescale distribution of the observed events, and find there are no significant short events of a few days, in spite of our high detection efficiency for short timescale events down to t_E = 0.3 days. We find that half of all our detected events have high magnification (>10). These events are useful for studies of extra-solar planets.

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Идентификаторы

DOI: 10.1086/375212

Цитирования и источники

Цитирований: 2Использованных источников: 0

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