Author
Zouhair Benkhaldoun
Other affiliations: University of Edinburgh, Max Planck Society, Yahoo! ...read more
Bio: Zouhair Benkhaldoun is an academic researcher from Cadi Ayyad University. The author has contributed to research in topics: Planet & Exoplanet. The author has an hindex of 25, co-authored 174 publications receiving 3458 citations. Previous affiliations of Zouhair Benkhaldoun include University of Edinburgh & Max Planck Society.
Topics: Planet, Exoplanet, Physics, Planetary system, Interferometry
Papers published on a yearly basis
Papers
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University of Liège1, University of Cambridge2, University of Bern3, University of Washington4, California Institute of Technology5, Massachusetts Institute of Technology6, Université de Namur7, Centre national de la recherche scientifique8, University of Paris9, Cadi Ayyad University10, University of California, San Diego11, University of Leicester12, Liverpool John Moores University13, University of Central Lancashire14, King Abdulaziz University15
TL;DR: The observations reveal that at least seven planets with sizes and masses similar to those of Earth revolve around TRAPPIST-1, and the six inner planets form a near-resonant chain, such that their orbital periods are near-ratios of small integers.
Abstract: One aim of modern astronomy is to detect temperate, Earth-like exoplanets that are well suited for atmospheric characterization. Recently, three Earth-sized planets were detected that transit (that is, pass in front of) a star with a mass just eight per cent that of the Sun, located 12 parsecs away. The transiting configuration of these planets, combined with the Jupiter-like size of their host star—named TRAPPIST-1—makes possible in-depth studies of their atmospheric properties with present-day and future astronomical facilities. Here we report the results of a photometric monitoring campaign of that star from the ground and space. Our observations reveal that at least seven planets with sizes and masses similar to those of Earth revolve around TRAPPIST-1. The six inner planets form a near-resonant chain, such that their orbital periods (1.51, 2.42, 4.04, 6.06, 9.1 and 12.35 days) are near-ratios of small integers. This architecture suggests that the planets formed farther from the star and migrated inwards. Moreover, the seven planets have equilibrium temperatures low enough to make possible the presence of liquid water on their surfaces.
1,476 citations
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University of Washington1, University of Bern2, University of Chicago3, Astrophysics Research Institute4, University of Liège5, University of California, San Diego6, California Institute of Technology7, University of Bordeaux8, Eclipse Internet9, University of Cambridge10, Ames Research Center11, Massachusetts Institute of Technology12, King Abdulaziz University13, University of Geneva14
TL;DR: The TRAPPIST-1 system is the first transiting planet system found orbiting an ultra-cool dwarf star as mentioned in this paper, which was unconstrained until now, and has a radius of 0.715 Earth radii and an equilibrium temperature of 169 K, placing it at the snow line.
Abstract: The TRAPPIST-1 system is the first transiting planet system found orbiting an ultra-cool dwarf star. At least seven planets similar to Earth in radius and in mass were previously found to transit this host star. Subsequently, TRAPPIST-1 was observed as part of the K2 mission and, with these new data, we report the measurement of an 18.764 d orbital period for the outermost planet, TRAPPIST-1h, which was unconstrained until now. This value matches our theoretical expectations based on Laplace relations and places TRAPPIST-1h as the seventh member of a complex chain, with three-body resonances linking every member. We find that TRAPPIST-1h has a radius of 0.715 Earth radii and an equilibrium temperature of 169 K, placing it at the snow line. We have also measured the rotational period of the star at 3.3 d and detected a number of flares consistent with an active, middle-aged, late M dwarf.
275 citations
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University of Washington1, University of Bern2, University of Chicago3, Astrophysics Research Institute4, University of Liège5, University of California, San Diego6, California Institute of Technology7, University of Bordeaux8, Eclipse Internet9, University of Cambridge10, Ames Research Center11, Massachusetts Institute of Technology12, King Abdulaziz University13, University of Geneva14
TL;DR: The TRAPPIST-1 system is the first transiting planet system found orbiting an ultra-cool dwarf star as discussed by the authors, which was unconstrained until now, and has a radius of 0.727 Earth radii and an equilibrium temperature of 173 K.
Abstract: The TRAPPIST-1 system is the first transiting planet system found orbiting an ultra-cool dwarf star. At least seven planets similar to Earth in radius and in mass were previously found to transit this host star. Subsequently, TRAPPIST-1 was observed as part of the K2 mission and, with these new data, we report the measurement of an 18.77 d orbital period for the outermost planet, TRAPPIST-1h, which was unconstrained until now. This value matches our theoretical expectations based on Laplace relations and places TRAPPIST-1h as the seventh member of a complex chain, with three-body resonances linking every member. We find that TRAPPIST-1h has a radius of 0.727 Earth radii and an equilibrium temperature of 173 K. We have also measured the rotational period of the star at 3.3 d and detected a number of flares consistent with a low-activity, middle-aged, late M dwarf.
218 citations
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University of Washington1, University of Zurich2, University of Bern3, University of Geneva4, University of Liège5, Massachusetts Institute of Technology6, Cadi Ayyad University7, University of California, San Diego8, California Institute of Technology9, University of Chicago10, Harvard University11, Centre national de la recherche scientifique12, University of Arizona13, University of Birmingham14
TL;DR: In this article, a photodynamical analysis of the Spitzer light curves was carried out to derive the density of the host star and the planet densities, and it was shown that all seven planets' densities may be described with a single rocky mass-radius relation which is depleted in iron relative to Earth, with Fe 21 wt % versus 32 wt% for Earth, and otherwise Earth-like in composition.
Abstract: We have collected transit times for the TRAPPIST-1 system with the Spitzer Space Telescope over four years. We add to these ground-based, HST and K2 transit time measurements, and revisit an N-body dynamical analysis of the seven-planet system using our complete set of times from which we refine the mass ratios of the planets to the star. We next carry out a photodynamical analysis of the Spitzer light curves to derive the density of the host star and the planet densities. We find that all seven planets' densities may be described with a single rocky mass-radius relation which is depleted in iron relative to Earth, with Fe 21 wt% versus 32 wt% for Earth, and otherwise Earth-like in composition. Alternatively, the planets may have an Earth-like composition, but enhanced in light elements, such as a surface water layer or a core-free structure with oxidized iron in the mantle. We measure planet masses to a precision of 3-5%, equivalent to a radial-velocity (RV) precision of 2.5 cm/sec, or two orders of magnitude more precise than current RV capabilities. We find the eccentricities of the planets are very small; the orbits are extremely coplanar; and the system is stable on 10 Myr timescales. We find evidence of infrequent timing outliers which we cannot explain with an eighth planet; we instead account for the outliers using a robust likelihood function. We forecast JWST timing observations, and speculate on possible implications of the planet densities for the formation, migration and evolution of the planet system.
142 citations
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TL;DR: In this article, the authors presented a new measurement for the parallax of TRAPPIST-1, 82.4 ± 0.8 mas, based on 188 epochs of observations from 2013 to 2016.
Abstract: TRAPPIST-1 is an ultracool dwarf star transited by seven Earth-sized planets, for which thorough characterization of atmospheric properties, surface conditions encompassing habitability, and internal compositions is possible with current and next-generation telescopes. Accurate modeling of the star is essential to achieve this goal. We aim to obtain updated stellar parameters for TRAPPIST-1 based on new measurements and evolutionary models, compared to those used in discovery studies. We present a new measurement for the parallax of TRAPPIST-1, 82.4 ± 0.8 mas, based on 188 epochs of observations with the TRAPPIST and Liverpool Telescopes from 2013 to 2016. This revised parallax yields an updated luminosity of L =(5.22 ± 0.19) x 10⁻⁴ Lʘ, which is very close to the previous estimate but almost two times more precise. We next present an updated estimate for TRAPPIST-1 stellar mass, based on two approaches: mass from stellar evolution modeling, and empirical mass derived from dynamical masses of equivalently classified ultracool dwarfs in astrometric binaries. We combine them using a Monte-Carlo approach to derive a semi-empirical estimate for the mass of TRAPPIST-1. We also derive estimate for the radius by combining this mass with stellar density inferred from transits, as well as an estimate for the effective temperature from our revised luminosity and radius. Our final results are M = 0.089 ± 0.006 Mʘ, R =0.121 ± 0.003 Rʘ , and Teff= 2516 ± 41 K. Considering the degree to which the TRAPPIST-1 system will be scrutinized in coming years, these revised and more precise stellar parameters should be considered when assessing the properties of TRAPPIST-1 planets.
103 citations
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1,288 citations
01 Dec 2006
TL;DR: In this article, NAFU SA and other role players expressed some criticism about government programmes. The criticism was not so much about the objectives and content of these programmes, but rather about their accessibility, or lack thereof, to emerging farmers.
Abstract: Recently NAFU SA and other role players expressed some criticism about government programmes. The criticism was not so much about the objectives and content of these programmes, but rather about their accessibility, or lack thereof, to emerging farmers.
819 citations
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TL;DR: The Spectro-Polarimetic High contrast imager for Exoplanets REsearch (SPHERE) was designed and built for the ESO Very Large Telescope (VLT) in Chile as mentioned in this paper.
Abstract: Observations of circumstellar environments to look for the direct signal of exoplanets and the scattered light from disks has significant instrumental implications. In the past 15 years, major developments in adaptive optics, coronagraphy, optical manufacturing, wavefront sensing and data processing, together with a consistent global system analysis have enabled a new generation of high-contrast imagers and spectrographs on large ground-based telescopes with much better performance. One of the most productive is the Spectro-Polarimetic High contrast imager for Exoplanets REsearch (SPHERE) designed and built for the ESO Very Large Telescope (VLT) in Chile. SPHERE includes an extreme adaptive optics system, a highly stable common path interface, several types of coronagraphs and three science instruments. Two of them, the Integral Field Spectrograph (IFS) and the Infra-Red Dual-band Imager and Spectrograph (IRDIS), are designed to efficiently cover the near-infrared (NIR) range in a single observation for efficient young planet search. The third one, ZIMPOL, is designed for visible (VIR) polarimetric observation to look for the reflected light of exoplanets and the light scattered by debris disks. This suite of three science instruments enables to study circumstellar environments at unprecedented angular resolution both in the visible and the near-infrared. In this work, we present the complete instrument and its on-sky performance after 4 years of operations at the VLT.
414 citations
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Aix-Marseille University1, University of Grenoble2, INAF3, Paris Diderot University4, Office National d'Études et de Recherches Aérospatiales5, ETH Zurich6, University of Lyon7, Max Planck Society8, European Southern Observatory9, Centre national de la recherche scientifique10, Astronomical Observatory of Capodimonte11, University of Chile12, Leiden University13, University of Amsterdam14, Space Telescope Science Institute15, University of Geneva16, Netherlands Institute for Space Research17, Diego Portales University18
TL;DR: The Spectro-Polarimetic High contrast imager for Exoplanets REsearch (SPHERE) was designed and built for the ESO Very Large Telescope (VLT) in Chile as discussed by the authors.
Abstract: Observations of circumstellar environments that look for the direct signal of exoplanets and the scattered light from disks have significant instrumental implications. In the past 15 years, major developments in adaptive optics, coronagraphy, optical manufacturing, wavefront sensing, and data processing, together with a consistent global system analysis have brought about a new generation of high-contrast imagers and spectrographs on large ground-based telescopes with much better performance. One of the most productive imagers is the Spectro-Polarimetic High contrast imager for Exoplanets REsearch (SPHERE), which was designed and built for the ESO Very Large Telescope (VLT) in Chile. SPHERE includes an extreme adaptive optics system, a highly stable common path interface, several types of coronagraphs, and three science instruments. Two of them, the Integral Field Spectrograph (IFS) and the Infra-Red Dual-band Imager and Spectrograph (IRDIS), were designed to efficiently cover the near-infrared range in a single observation for an efficient search of young planets. The third instrument, ZIMPOL, was designed for visible polarimetric observation to look for the reflected light of exoplanets and the light scattered by debris disks. These three scientific instruments enable the study of circumstellar environments at unprecedented angular resolution, both in the visible and the near-infrared. In this work, we thoroughly present SPHERE and its on-sky performance after four years of operations at the VLT.
378 citations