Author
Man Cheung Alex Li
Other affiliations: Max Planck Society
Bio: Man Cheung Alex Li is an academic researcher from University of Auckland. The author has contributed to research in topics: Gravitational microlensing & Planet. The author has an hindex of 21, co-authored 114 publications receiving 1909 citations. Previous affiliations of Man Cheung Alex Li include Max Planck Society.
Papers
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TL;DR: In this article, the authors report the results of the statistical analysis of planetary signals discovered in MOA-II microlensing survey alert system events from 2007 to 2012, and determine the survey sensitivity as a function of planet star mass ratio, q, and projected planet star separation, s, in Einstein radius units.
Abstract: We report the results of the statistical analysis of planetary signals discovered in MOA-II microlensing survey alert system events from 2007 to 2012. We determine the survey sensitivity as a function of planet star mass ratio, q, and projected planet star separation, s, in Einstein radius units. We find that the mass-ratio function is not a single power law, but has a change in slope at q approx.10(exp -4), corresponding to approx. 20 Stellar Mass for the median host-star mass of approx. 0.6 M. We find significant planetary signals in 23 of the 1474 alert events that are well-characterized by the MOA-II survey data alone. Data from other groups are used only to characterize planetary signals that have been identified in the MOA data alone. The distribution of mass ratios and separations of the planets found in our sample are well fit by a broken power-law model. We also combine this analysis with the previous analyses of Gould et al. and Cassan et al., bringing the total sample to 30 planets. The unbroken power-law model is disfavored with a p-value of 0.0022, which corresponds to a Bayes factor of 27 favoring the broken power-law model. These results imply that cold Neptunes are likely to be the most common type of planets beyond the snow line.
227 citations
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Las Cumbres Observatory Global Telescope Network1, University of Warsaw2, California Institute of Technology3, University of Salerno4, University of Copenhagen5, Ohio State University6, Harvard University7, Heidelberg University8, University of Notre Dame9, University of St Andrews10, Qatar Foundation11, Istituto Nazionale di Fisica Nucleare12, University of Hamburg13, Institut d'Astrophysique de Paris14, Max Planck Society15, Peking University16, Keele University17, Chinese Academy of Sciences18, Korea Astronomy and Space Science Institute19, European Southern Observatory20, Space Telescope Science Institute21, University of Antofagasta22, Pontifical Catholic University of Chile23, Sharif University of Technology24, Aarhus University25, Open University26, Liverpool John Moores University27, University of Warwick28, Nagoya University29, Massey University30, University of Auckland31, Osaka University32, Kyoto Sangyo University33, Vaughn College of Aeronautics and Technology34, Victoria University of Wellington35, Chungbuk National University36
TL;DR: In this paper, the authors reported the detection of a cold Neptune mplanet = 21 ± 2 M⊕ orbiting a 0.38 m⊙ M dwarf lying 2.5-3.3 kpc toward the Galactic center as part of a campaign combining ground-based and Spitzer observations.
Abstract: We report the detection of a cold Neptune mplanet = 21 ± 2 M⊕ orbiting a 0.38 M⊙ M dwarf lying 2.5–3.3 kpc toward the Galactic center as part of a campaign combining ground-based and Spitzer observations to measure the Galactic distribution of planets. This is the first time that the complex real-time protocols described by Yee et al., which aim to maximize planet sensitivity while maintaining sample integrity, have been carried out in practice. Multiple survey and follow up teams successfully combined their efforts within the framework of these protocols to detect this planet. This is the second planet in the Spitzer Galactic distribution sample. Both are in the near to mid-disk and are clearly not in the Galactic bulge.
103 citations
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University of Notre Dame1, Goddard Space Flight Center2, University of Warsaw3, Max Planck Society4, Korea Astronomy and Space Science Institute5, Ohio State University6, Heidelberg University7, Las Cumbres Observatory Global Telescope Network8, Institut d'Astrophysique de Paris9, Massey University10, University of Tasmania11, University of Auckland12, Yale University13, Pennsylvania State University14, Space Telescope Science Institute15, Nagoya University16, Osaka University17, Vaughn College of Aeronautics and Technology18, Victoria University of Wellington19, Kyoto Sangyo University20, Texas A&M University21, Weizmann Institute of Science22, Chungbuk National University23, Qatar Foundation24, University of St Andrews25, Open University26, Liverpool John Moores University27, University of Canterbury28, University of Rijeka29, University of Vienna30, University of Toulouse31, Niels Bohr Institute32, San Francisco State University33, Curtin University34
TL;DR: The OGLE-2007-BLG-349 microlensing event has a strong planetary signal that is best fit with a mass ratio q ≈ 3.4 × 10-4, but there is an additional signal due to an additional lens mass, either another planet or another star as mentioned in this paper.
Abstract: © 2016. The American Astronomical Society. All rights reserved.We present the analysis of the first circumbinary planet microlensing event, OGLE-2007-BLG-349. This event has a strong planetary signal that is best fit with a mass ratio of q ≈ 3.4 × 10-4, but there is an additional signal due to an additional lens mass, either another planet or another star. We find acceptable light-curve fits with two classes of models: two-planet models (with a single host star) and circumbinary planet models. The light curve also reveals a significant microlensing parallax effect, which constrains the mass of the lens system to be M L ≈ 0.7 M⊙. Hubble Space Telescope (HST) images resolve the lens and source stars from their neighbors and indicate excess flux due to the star(s) in the lens system. This is consistent with the predicted flux from the circumbinary models, where the lens mass is shared between two stars, but there is not enough flux to be consistent with the two-planet, one-star models. So, only the circumbinary models are consistent with the HST data. They indicate a planet of mass m c = 80 ± 13 M⊙, orbiting a pair of M dwarfs with masses of M A = 0.41 ± 0.07 and M B = 0.30 ± 0.07, which makes this the lowest-mass circumbinary planet system known. The ratio of the separation between the planet and the center of mass to the separation of the two stars is ∼40, so unlike most of the circumbinary planets found by Kepler, the planet does not orbit near the stability limit.
89 citations
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Massey University1, Goddard Space Flight Center2, Osaka University3, University of Warsaw4, University of Auckland5, Istituto Nazionale di Fisica Nucleare6, University of Salerno7, Nagoya University8, University of Notre Dame9, College of Industrial Technology10, Victoria University of Wellington11, University of Canterbury12, Kyoto Sangyo University13, Ohio State University14, University of Warwick15
TL;DR: In this paper, the authors reported the discovery of the lowest mass ratio exoplanet to be found by the microlensing method in the light curve of the event OGLE 2016 -BLG-1195.
Abstract: We report discovery of the lowest mass ratio exoplanet to be found by the microlensing method in the light curve of the event OGLE 2016 –BLG–1195. This planet revealed itself as a smalldeviation from a microlensing single lens profile from an examination of the survey data. Theduration of the planetary signal is ~ 2.5 h. The measured ratio of the planet mass to its hos tstar is q = 4.2 ± 0.7 x 10 -5(exp). We further estimate that the lens system is likely to comprise a cold ~3 Earth mass planet in an ~2 au wide orbit around a 0.2 Solar mass star at an overall distance of 7.1 kpc.
77 citations
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California Institute of Technology1, Ohio State University2, University of Warsaw3, Las Cumbres Observatory Global Telescope Network4, Goddard Space Flight Center5, New York University6, Ames Research Center7, Osaka University8, Nagoya University9, University of Notre Dame10, Massey University11, University of Auckland12, Vaughn College of Aeronautics and Technology13, Victoria University of Wellington14, Kyoto Sangyo University15, Qatar Foundation16, Institut d'Astrophysique de Paris17, University of St Andrews18, University of Copenhagen19, Tsinghua University20, Chinese Academy of Sciences21, University of Manchester22, Heidelberg University23, Open University24, Liverpool John Moores University25, Istituto Nazionale di Fisica Nucleare26, University of Salerno27, University of Hamburg28, Max Planck Society29, Keele University30, University of Göttingen31, Korea Astronomy and Space Science Institute32, Pontifical Catholic University of Chile33, Sharif University of Technology34, University of Antofagasta35, University of Colorado Boulder36, University of Tasmania37, University of Washington38, Tel Aviv University39, University of Toronto40, Subaru41, Australian National University42, Institut de Ciències de l'Espai43, University of Porto44, University of Tokyo45
TL;DR: The demographic questions that can be addressed by this program, including the frequency of FFPs and the Galactic distribution of exoplanets, the observational parameters of K2C9, and the array of resources dedicated to concurrent observations are detailed.
Abstract: K2's Campaign 9 (K2C9) will conduct a ~3.7 deg^2 survey toward the Galactic bulge from 2016 April 22 through July 2 that will leverage the spatial separation between K2 and the Earth to facilitate measurement of the microlens parallax πE for ≳170 microlensing events. These will include several that are planetary in nature as well as many short-timescale microlensing events, which are potentially indicative of free-floating planets (FFPs). These satellite parallax measurements will in turn allow for the direct measurement of the masses of and distances to the lensing systems. In this article we provide an overview of the K2C9 space- and ground-based microlensing survey. Specifically, we detail the demographic questions that can be addressed by this program, including the frequency of FFPs and the Galactic distribution of exoplanets, the observational parameters of K2C9, and the array of resources dedicated to concurrent observations. Finally, we outline the avenues through which the larger community can become involved, and generally encourage participation in K2C9, which constitutes an important pathfinding mission and community exercise in anticipation of WFIRST.
73 citations
Cited by
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Peking University1, University of Arizona2, Leiden University3, University of Leicester4, University of Cambridge5, University of Milan6, Vassar College7, Smith College8, University of Grenoble9, University of Victoria10, Chinese Academy of Sciences11, Max Planck Society12, Rice University13, University of Paris14, European Southern Observatory15, University of Chicago16, INAF17, Space Telescope Science Institute18, Ames Research Center19
TL;DR: In this article, the authors identify the most frequently revealed substructure in ALMA dust observations of protoplanetary disks, and measure their properties to investigate how they form, including axisymmetric rings and gaps.
Abstract: Rings are the most frequently revealed substructure in ALMA dust observations of protoplanetary disks, but their origin is still hotly debated. In this paper, we identify dust substructures in 12 disks and measure their properties to investigate how they form. This subsample of disks is selected from a high-resolution ($\sim0.12''$) ALMA 1.33 mm survey of 32 disks in the Taurus star-forming region, which was designed to cover a wide range of sub-mm brightness and to be unbiased to previously known substructures. While axisymmetric rings and gaps are common within our sample, spiral patterns and high contrast azimuthal asymmetries are not detected. Fits of disk models to the visibilities lead to estimates of the location and shape of gaps and rings, the flux in each disk component, and the size of the disk. The dust substructures occur across a wide range of stellar mass and disk brightness. Disks with multiple rings tend to be more massive and more extended. The correlation between gap locations and widths, the intensity contrast between rings and gaps, and the separations of rings and gaps could all be explained if most gaps are opened by low-mass planets (super-Earths and Neptunes) in the condition of low disk turbulence ($\alpha=10^{-4}$). The gap locations are not well correlated with the expected locations of CO and N$_2$ ice lines, so condensation fronts are unlikely to be a universal mechanism to create gaps and rings, though they may play a role in some cases.
395 citations
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TL;DR: In this paper, a growth model and Monte Carlo simulations are used to demonstrate that many intermediate-size exoplanets are water worlds, which matches the second peak of the exoplanet radius bimodal distribution.
Abstract: The radii and orbital periods of 4,000+ confirmed/candidate exoplanets have been precisely measured by the Kepler mission. The radii show a bimodal distribution, with two peaks corresponding to smaller planets (likely rocky) and larger intermediate-size planets, respectively. While only the masses of the planets orbiting the brightest stars can be determined by ground-based spectroscopic observations, these observations allow calculation of their average densities placing constraints on the bulk compositions and internal structures. However, an important question about the composition of planets ranging from 2 to 4 Earth radii (R⊕) still remains. They may either have a rocky core enveloped in a H2-He gaseous envelope (gas dwarfs) or contain a significant amount of multicomponent, H2O-dominated ices/fluids (water worlds). Planets in the mass range of 10-15 M⊕, if half-ice and half-rock by mass, have radii of 2.5 R⊕, which exactly match the second peak of the exoplanet radius bimodal distribution. Any planet in the 2- to 4-R⊕ range requires a gas envelope of at most a few mass percentage points, regardless of the core composition. To resolve the ambiguity of internal compositions, we use a growth model and conduct Monte Carlo simulations to demonstrate that many intermediate-size planets are "water worlds."
331 citations
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TL;DR: The Ecliptic Plane Input Catalog (EPIC) as mentioned in this paper provides coordinates, photometry and kinematics based on a federation of all-sky catalogs to support target selection and target management for the K2 mission.
Abstract: The K2 Mission uses the Kepler spacecraft to obtain high-precision photometry over ~80 day campaigns in the ecliptic plane. The Ecliptic Plane Input Catalog (EPIC) provides coordinates, photometry and kinematics based on a federation of all-sky catalogs to support target selection and target management for the K2 mission. We describe the construction of the EPIC, as well as modifications and shortcomings of the catalog. Kepler magnitudes (Kp) are shown to be accurate to ~0.1 mag for the Kepler field, and the EPIC is typically complete to Kp~17 (Kp~19 for campaigns covered by SDSS). We furthermore classify 138,600 targets in Campaigns 1-8 (~88% of the full target sample) using colors, proper motions, spectroscopy, parallaxes, and galactic population synthesis models, with typical uncertainties for G-type stars of ~3% in Teff, ~0.3 dex in log(g), ~40% in radius, ~10% in mass, and ~40% in distance. Our results show that stars targeted by K2 are dominated by K-M dwarfs (~41% of all selected targets), F-G dwarfs (~36%) and K giants (~21%), consistent with key K2 science programs to search for transiting exoplanets and galactic archeology studies using oscillating red giants. However, we find a significant variation of the fraction of cool dwarfs with galactic latitude, indicating a target selection bias due to interstellar reddening and the increased contamination by giant stars near the galactic plane. We discuss possible systematic errors in the derived stellar properties, and differences to published classifications for K2 exoplanet host stars. The EPIC is hosted at the Mikulski Archive for Space Telescopes (MAST): this http URL.
321 citations
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TL;DR: In this paper, the abundance of primordial black holes (PBH) using microlensing events obtained from 5-years observations of stars in the Galactic bulge by the Optical Gravitational Lensing Experiment (OGLE) is constrain.
Abstract: We constrain the abundance of primordial black holes (PBH) using 2622 microlensing events obtained from 5-years observations of stars in the Galactic bulge by the Optical Gravitational Lensing Experiment (OGLE). The majority of microlensing events display a single or at least continuous population that has a peak around the light curve timescale ${t}_{\mathrm{E}}\ensuremath{\simeq}20\text{ }\text{ }\mathrm{days}$ and a wide distribution over the range ${t}_{\mathrm{E}}\ensuremath{\simeq}[1,300]\text{ }\text{ }\mathrm{days}$, while the data also indicates a second population of 6 ultrashort-timescale events in ${t}_{\mathrm{E}}\ensuremath{\simeq}[0.1,0.3]\text{ }\text{ }\mathrm{days}$, which are advocated to be due to free-floating planets. We confirm that the main population of OGLE events can be well modeled by microlensing due to brown dwarfs, main sequence stars and stellar remnants (white dwarfs and neutron stars) in the standard Galactic bulge and disk models for their spatial and velocity distributions. Using the dark matter (DM) model for the Milky Way (MW) halo relative to the Galactic bulge/disk models, we obtain the tightest upper bound on the PBH abundance in the mass range ${M}_{\mathrm{PBH}}\ensuremath{\simeq}[{10}^{\ensuremath{-}6},{10}^{\ensuremath{-}3}]\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ (Earth-Jupiter mass range), if we employ the ``null hypothesis'' that the OGLE data does not contain any PBH microlensing event. More interestingly, we also show that Earth-mass PBHs can well reproduce the 6 ultrashort-timescale events, without the need of free-floating planets, if the mass fraction of PBH to DM is at a per cent level, which is consistent with other constraints such as the microlensing search for Andromeda galaxy (M31) and the longer timescale OGLE events. Our result gives a hint of PBH existence, and can be confirmed or falsified by microlensing search for stars in M31, because M31 is towards the MW halo direction and should therefore contain a much less number of free-floating planets, even if exist, than the direction to the MW center.
250 citations
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TL;DR: In this article, the authors report the results of the statistical analysis of planetary signals discovered in MOA-II microlensing survey alert system events from 2007 to 2012, and determine the survey sensitivity as a function of planet star mass ratio, q, and projected planet star separation, s, in Einstein radius units.
Abstract: We report the results of the statistical analysis of planetary signals discovered in MOA-II microlensing survey alert system events from 2007 to 2012. We determine the survey sensitivity as a function of planet star mass ratio, q, and projected planet star separation, s, in Einstein radius units. We find that the mass-ratio function is not a single power law, but has a change in slope at q approx.10(exp -4), corresponding to approx. 20 Stellar Mass for the median host-star mass of approx. 0.6 M. We find significant planetary signals in 23 of the 1474 alert events that are well-characterized by the MOA-II survey data alone. Data from other groups are used only to characterize planetary signals that have been identified in the MOA data alone. The distribution of mass ratios and separations of the planets found in our sample are well fit by a broken power-law model. We also combine this analysis with the previous analyses of Gould et al. and Cassan et al., bringing the total sample to 30 planets. The unbroken power-law model is disfavored with a p-value of 0.0022, which corresponds to a Bayes factor of 27 favoring the broken power-law model. These results imply that cold Neptunes are likely to be the most common type of planets beyond the snow line.
227 citations