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

Abe, F.; Bennett, D. P.; Bond, I. A.; Eguchi, S.; Furuta, Y.; Hearnshaw, John; Kamiya, K.; Kilmartin, P. M.; Kurata, Yoshimasa; Masuda, K.; Matsubara, Y.; Muraki, Y.; Noda, S.; Okajima, Kazuhisa; Rakich, Andrew; Rattenbury, N. J.; Sako, T.; Sekiguchi, T.; Sullivan, D. J.; Sumi, T.; Tristram, P. J.; Yanagisawa, Takufumi; Yock, P. C. M.; Gal‐Yam, A.; Lipkin, Y.; Maoz, D.; Ofek, E. O.; Udalski, A.; Szewczyk, O.; Zebrun, K.; Soszyński, I.; Szymański, M. K.; Kubiak, M.; Pietrzyński, G.; Wyrzykowski, Ł.

doi:10.1126/science.1100714

Cited by 62 publications

(34 citation statements)

References 27 publications

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“…Currently, the highest priority is given to high-magnification events (Bond et al 2002b;Abe et al 2004;Rattenbury et al 2002). This is based on the fact that in addition to a major caustic located away from the primary lens (planetary caustic), a planet induces an additional tiny caustic in the region close to the primary lens (stellar or central caustic).…”

Section: Introductionmentioning

confidence: 99%

Microlensing Zone of Planets Detectable Through the Channel of High-Magnification Events

Han

2009

ApJ

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A microlensing lensing zone refers to the range of planet-star separations where the probability of detecting a planetary signal is high. Its conventional definition as the range between ∼ 0.6 and 1.6 Einstein radii of the primary lens is based on the criterion that a major caustic induced by a planet should be located within the Einstein ring of the primary. However, current planetary lensing searches focus on high-magnification events to detect perturbations induced by another caustic located always within the Einstein ring very close to the primary lens (stellar caustic) and thus a new definition of a lensing zone is needed. In this paper, we determine this lensing zone. By applying a criterion that detectable planets should produce signals ≥ 5%, we find that the new lensing zone varies depending on the planet/star mass ratio unlike the fixed range of the classical zone regardless of the mass ratio. The lensing zone is equivalent to the classical zone for a planet with a planet/star mass ratio q ∼ 3 × 10 −4 and it becomes wider for heavier planets. For a Jupiter-mass planet, the lensing zone ranges from 0.25 to 3.9 Einstein radii, corresponding to a physical range between ∼ 0.5 AU and 7.4 AU for a typical Galactic event. The wider lensing zone of central perturbations for giant planets implies that the microlensing method provides an important tool to detect planetary systems composed of multiple ice-giant planets.

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Section: Introductionmentioning

confidence: 99%

Microlensing Zone of Planets Detectable Through the Channel of High-Magnification Events

Han

2009

ApJ

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“…The absence of perturbations to stellar microlensing events can be used to constrain the presence of planetary lens companions. With large samples of events, upper limits on the frequency of Jupiter-mass planets have been placed over an orbital range of 1-10 AU, down to M % planets [15][16][17] From analysis of colour-magnitude diagrams, we derive the following reddening-corrected colours and magnitudes for the source star: (V 2 I) 0 ¼ 0.85, I 0 ¼ 14.25 and (V 2 K) 0 ¼ 1.9. We used the surface brightness relation 20 linking the emerging flux per solid angle of a light-emitting body to its colour, calibrated by interferometric observations, to derive an angular radius of 5.25^0.73 mas, which corresponds to a source radius of 9.6^1.3R ( (where R ( is the radius of the Sun) if the source star is at a distance of 8.5 kpc.…”

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confidence: 99%

Discovery of a cool planet of 5.5 Earth masses through gravitational microlensing

Beaulieu¹,

Bennett²,

Fouqué³

et al. 2006

Nature

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545

350

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In the favoured core-accretion model of formation of planetary systems, solid planetesimals accumulate to build up planetary cores, which then accrete nebular gas if they are sufficiently massive. Around M-dwarf stars (the most common stars in our Galaxy), this model favours the formation of Earth-mass (M % ) to Neptune-mass planets with orbital radii of 1 to 10 astronomical units (AU), which is consistent with the small number of gas giant planets known to orbit M-dwarf host stars 1-4 . More than 170 extrasolar planets have been discovered with a wide range of masses and orbital periods, but planets of Neptune's mass or less have not hitherto been detected at separations of more than 0.15 AU from normal stars. Here we report the discovery of a 5.5 15.5 22.7 M % planetary companion at a separation of 2.6 11.5 20.6 AU from a 0.22 10.21 20.11 M ( M-dwarf star, where M ( refers to a solar mass. (We propose to name it OGLE-2005-BLG-390Lb, indicating a planetary mass companion to the lens star of the microlensing event.) The mass is lower than that of GJ876d (ref. 5), although the error bars overlap. Our detection suggests that such cool, sub-Neptune-mass planets may be more common than gas giant planets, as predicted by the core accretion theory.Gravitational microlensing events can reveal extrasolar planets orbiting the foreground lens stars if the light curves are measured frequently enough to characterize planetary light curve deviations with features lasting a few hours 6-9 . Microlensing is most sensitive to planets in Earth-to-Jupiter-like orbits with semi-major axes in the range 1-5 AU. The sensitivity of the microlensing method to lowmass planets is restricted by the finite angular size of the source stars 10,11 , limiting detections to planets of a few M % for giant source stars, but allowing the detection of planets as small as 0.1M % for main-sequence source stars in the Galactic Bulge. The PLANET collaboration 12 maintains the high sampling rate required to detect low-mass planets while monitoring the most promising of the .500 microlensing events discovered annually by the OGLE collaboration, as well as events discovered by MOA. A decade of pioneering microlensing searches has resulted in the recent detections of two Jupiter-mass extrasolar planets 13,14 with orbital separations of a few AU by the combined observations of the OGLE, MOA, MicroFUN and PLANET collaborations. The absence of perturbations to stellar microlensing events can be used to constrain the presence of planetary lens companions. With large samples of events, upper LETTERS 1 PLANET/RoboNet Collaboration

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“…Planetary exclusion zones were produced for event MOA-2003-BLG-32/OGLE-2003-BLG-219 where the FWHM of the event peak was intensively monitored. The observations eliminated the presence of gas-giant and ice-giant mass planets over a wide range of orbit radii 43,44 . Such well-sampled high amplification light curves can help determine the fraction and character of planetary systems in the Galaxy.…”

Section: Single Lensesmentioning

confidence: 97%

“…The sensitivity of high amplification events to lens system planets has been demonstrated in a number of microlensing events 41,42,39,40,43,30,44 . Given sufficient temporal coverage of the event peak, planets can be excluded from the lens star system.…”

Section: Single Lensesmentioning

confidence: 99%

Planetary Microlensing: From Prediction to Discovery

Rattenbury

2006

Mod. Phys. Lett. A

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Received (Day Month Year) Revised (Day Month Year)Four planets have recently been discovered by gravitational microlensing. The most recent of these discoveries is the lowest-mass planet known to exist around a normal star. The detection of planets in gravitational microlensing events was predicted over a decade ago. Microlensing is now a mature field of astrophysical research and the recent planet detections herald a new chapter in the hunt for low mass extra-solar planets. This paper reviews the basic theory of planetary microlensing, describes the experiments currently in operation for the detection and observation of microlensing events and compares the characteristics of the planetary systems found to date by microlensing. Some proposed schemes for improving the detection rate of planets via microlensing are also discussed.

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

Cited by 62 publications

References 27 publications

Microlensing Zone of Planets Detectable Through the Channel of High-Magnification Events

Microlensing Zone of Planets Detectable Through the Channel of High-Magnification Events

Discovery of a cool planet of 5.5 Earth masses through gravitational microlensing

Planetary Microlensing: From Prediction to Discovery

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