MOA-cam3: a wide-field mosaic CCD camera for a gravitational microlensing survey in New Zealand

Sako, T.; Sekiguchi, T.; Sasaki, M.; Okajima, Kazuhisa; Abe, F.; Bond, I. A.; Hearnshaw, John; Itow, Y.; Kamiya, K.; Kilmartin, P. M.; Masuda, K.; Matsubara, Y.; Muraki, Y.; Rattenbury, N. J.; Sullivan, D. J.; Sumi, T.; Tristram, P. J.; Yanagisawa, Takufumi; Yock, P. C. M.

doi:10.1007/s10686-007-9082-5

Cited by 135 publications

(61 citation statements)

References 16 publications

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“…Unlike other techniques, such as the transit method or radial velocities, the microlensing technique is sensitive to planets on wide orbits around the snow line of the system (Gaudi 2012). Currently, the main microlensing surveys for exoplanets are the Optical Gravitational Lensing Experiment (OGLE; Udalski 2003) and the Microlensing Observations in Astrophysics (MOA; Sako et al 2008). To date, a total number of 26 planets have been detected by these surveys.…”

Section: Discussionmentioning

confidence: 99%

Diversity of planetary systems in low-mass disks

Ronco

Elía

2014

A&A

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Context. Several studies, observational and theoretical, suggest that planetary systems with only rocky planets are the most common in the Universe. Aims. We study the diversity of planetary systems that might form around Sun-like stars in low-mass disks without gas-giant planets. We focus especially on the formation process of terrestrial planets in the habitable zone (HZ) and analyze their water contents with the goal to determine systems of astrobiological interest. In addition, we study the formation of planets on wide orbits because they can be detected with the microlensing technique. Methods. N-body simulations of high resolution were developed for a wide range of surface density profiles. A bimodal distribution of planetesimals and planetary embryos with different physical and orbital configurations was used to simulate the planetary accretion process. The surface density profile combines a power law for the inside of the disk of the form r −γ , with an exponential decay to the outside. We performed simulations adopting a disk of 0.03 M and values of γ = 0.5, 1 and 1.5. Results. All our simulations form planets in the HZ with different masses and final water contents depending on the three different profiles. For γ = 0.5, our simulations produce three planets in the HZ with masses ranging from 0.03 M ⊕ to 0.1 M ⊕ and water contents between 0.2 and 16 Earth oceans (1 Earth ocean = 2.8 × 10 −4 M ⊕ ). For γ = 1, three planets form in the HZ with masses between 0.18 M ⊕ and 0.52 M ⊕ and water contents from 34 to 167 Earth oceans. Finally, for γ = 1.5, we find four planets in the HZ with masses ranging from 0.66 M ⊕ to 2.21 M ⊕ and water contents between 192 and 2326 Earth oceans. This profile shows distinctive results because it is the only one of those studied here that leads to the formation of water worlds. Conclusions. Since planetary systems with γ = 1 and 1.5 present planets in the HZ with suitable masses to retain a long-lived atmosphere and to maintain plate tectonics, they seem to be the most promising candidates to be potentially habitable. Particularly, these systems form Earths and Super-Earths of at least 3 M ⊕ around the snow line, which can be discovered by the microlensing technique.

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Section: Discussionmentioning

confidence: 99%

Diversity of planetary systems in low-mass disks

Ronco

Elía

2014

A&A

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“…Currently, the main microlensing surveys for exoplanets are the Optical Gravitational Lensing Experiment (OGLE; Udalski 2003) and the Microlensing Observations in Astrophysics (MOA; Sako et al 2008). To date, microlensing has detected a total number of 18 planets, which are distributed on a plane semimajor axis-mass as in Fig.…”

Section: Discussionmentioning

confidence: 99%

Terrestrial planets in high-mass disks without gas giants

Elía

Guilera

Brunini

2013

A&A

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Context. Observational and theoretical studies suggest that planetary systems consisting only of rocky planets are probably the most common in the Universe. Aims. We study the potential habitability of planets formed in high-mass disks without gas giants around solar-type stars. These systems are interesting because they are likely to harbor super-Earths or Neptune-mass planets on wide orbits, which one should be able to detect with the microlensing technique. Methods. First, a semi-analytical model was used to define the mass of the protoplanetary disks that produce Earth-like planets, superEarths, or mini-Neptunes, but not gas giants. Using mean values for the parameters that describe a disk and its evolution, we infer that disks with masses lower than 0.15 M are unable to form gas giants. Then, that semi-analytical model was used to describe the evolution of embryos and planetesimals during the gaseous phase for a given disk. Thus, initial conditions were obtained to perform N-body simulations of planetary accretion. We studied disks of 0.1, 0.125, and 0.15 M . Results. All our simulations form massive planets on wide orbits. For a 0.1 M disk, 2-3 super-Earths of 2.8 to 5.9 M ⊕ are formed between 2 and 5 AU. For disks of 0.125 and 0.15 M , our simulations produce a 10-17.1 M ⊕ planet between 1.6 and 2.7 AU, and other super-Earths are formed in outer regions. Moreover, six planets survive in the habitable zone (HZ). These planets have masses from 1.9 to 4.7 M ⊕ and significant water contents ranging from 560 to 7482 Earth oceans, where one Earth ocean represents the amount of water on Earth's surface, which equals 2.8 × 10 −4 M ⊕ . Of the six planets formed in the HZ, three are water worlds with 39%-44% water by mass. These planets start the simulations beyond the snow line, which explains their high water abundances. In general terms, the smaller the mass of the planets observed on wide orbits, the higher the possibility to find water worlds in the HZ. In fact, massive planets can act as a dynamical barrier that prevents the inward diffusion of water-rich embryos located beyond the snow line. Conclusions. Systems without gas giants that harbor super-Earths or Neptune-mass planets on wide orbits around solar-type stars are of astrobiological interest. These systems are likely to harbor super-Earths in the HZ with significant water contents, which missions such as Kepler and Darwin should be able to find.

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“…Hillenbrand & Carpenter 2000;Allers et al 2007;Luhman et al 2007a), recent studies, in particular those by the Substellar Objects in Nearby Young Clusters (SONYC) group, have focused on obtaining confirma-tion spectra of such candidates and have verified several free-floating, planetary-mass objects with masses as low as a few Jupiter masses (Scholz et al 2009(Scholz et al , 2012aMužić et al 2011Mužić et al , 2012Mužić et al , 2015. Sumi et al (2011) also present evidence for a large population of ∼Jupiter-mass objects that are either wide-separation (a 10 AU) or free-floating planets inferred from an excess of short events in the observed timescale distribution of a sample of microlensing events collected by the second phase of the Microlensing Observations in Astrophysics group (MOA-II; Sumi et al 2003;Sako et al 2008). Wyrzykowski et al (2015) report that data from the third phase of the Optical Gravitational Lensing Experiment (OGLE-III; Udalski 2003) show a flattening in the slope of the observed event timescale distribution towards shorter timescales that is suggestive of a population of lenses similar to that reported by Sumi et al (2011), although this flattening is only marginally significant due to uncertainties resulting from small-number statistics and a low detection efficiency to such shorttimescale events.…”

Section: Introductionmentioning

confidence: 99%

Constraining the Frequency of Free-Floating Planets From a Synthesis of Microlensing, Radial Velocity, and Direct Imaging Survey Results

Clanton

Gaudi

2016

ApJ

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A microlensing survey by Sumi et al. (2011) exhibits an overabundance of short-timescale events (t E 2 days) relative to that expected from known stellar populations and a smooth power-law extrapolation down to the brown dwarf regime. This excess has been interpreted as a population of approximately Jupiter-mass objects that outnumber main-sequence stars by nearly twofold; however the microlensing data alone cannot distinguish between events due to wide-separation (a 10 AU) and free-floating planets. Assuming these short-timescale events are indeed due to planetary-mass objects, we aim to constrain the fraction of these events that can be explained by bound but wideseparation planets. We fit the observed timescale distribution with a lens mass function comprised of brown dwarfs, main-sequence stars, white dwarfs, neutron stars, and black holes, finding and thus corroborating the initial identification of an excess of short-timescale events. Including a population of bound planets with distributions of masses and separations that are consistent with the results from representative microlensing, radial velocity, and direct imaging surveys, we then determine what fraction of these bound planets are expected not to show signatures of the primary lens (host) star in their microlensing light curves, and thus what fraction of the short-timescale event excess can be explained by bound planets alone. We find that, given our model for the distribution of planet parameters, bound planets alone cannot explain the entire excess without violating the constraints from the surveys we consider, and thus some fraction of these events must be due to free-floating planets, if our model for bound planets holds. We estimate a median fraction of short-timescale events due to free-floating planets to be f = 0.67 (0.23-0.85 at 95% confidence) when assuming "hot-start" planet evolutionary models and f = 0.58 (0.14-0.83 at 95% confidence) for "cold-start" models. Assuming a delta-function distribution of free-floating planets of mass m p = 2 M Jup yields a number of free-floating planets per main sequence star of N = 1.4 (0.48-1.8 at 95% confidence) in the "hot-start" case and N = 1.2 (0.29-1.8 at 95% confidence) in the "cold-start" case.

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MOA-cam3: a wide-field mosaic CCD camera for a gravitational microlensing survey in New Zealand

Cited by 135 publications

References 16 publications

Diversity of planetary systems in low-mass disks

Diversity of planetary systems in low-mass disks

Terrestrial planets in high-mass disks without gas giants

Constraining the Frequency of Free-Floating Planets From a Synthesis of Microlensing, Radial Velocity, and Direct Imaging Survey Results

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