References of "Gillon, Michaël"
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See detailWASP-147b, 160Bb, 164b and 165b: two hot Saturns and two Jupiters, including two planets with metal-rich hosts
Lendl, M.; Anderson, D. R.; Bonfanti, Andrea ULiege et al

in Monthly Notices of the Royal Astronomical Society (2018)

We report the discovery of four transiting hot Jupiters, WASP-147, WASP-160B, WASP-164 and WASP-165 from the WASP survey. WASP-147b is a near Saturn-mass (M[SUB]P[/SUB] = 0.28M[SUB]J[/SUB]) object with a ... [more ▼]

We report the discovery of four transiting hot Jupiters, WASP-147, WASP-160B, WASP-164 and WASP-165 from the WASP survey. WASP-147b is a near Saturn-mass (M[SUB]P[/SUB] = 0.28M[SUB]J[/SUB]) object with a radius of 1.11 R[SUB]J[/SUB] orbiting a G4 star with a period of 4.6 d. WASP-160Bb has a mass and radius (M[SUB]p[/SUB] = 0.28 M[SUB]J[/SUB], R[SUB]p[/SUB] = 1.09 R[SUB]J[/SUB]) near-identical to WASP-147b, but is less irradiated, orbiting a metal-rich ([Fe/H][SUB]*[/SUB] = 0.27) K0 star with a period of 3.8 d. WASP-160B is part of a near equal-mass visual binary with an on-sky separation of 28.5 arcsec. WASP-164b is a more massive (M[SUB]P[/SUB] = 2.13 M[SUB]J[/SUB], R[SUB]p[/SUB] = 1.13 R[SUB]J[/SUB]) hot Jupiter, orbiting a G2 star on a close-in (P = 1.8 d), but tidally stable orbit. WASP-165b is a classical (M[SUB]p[/SUB] = 0.66 M[SUB]J[/SUB], R[SUB]P[/SUB] = 1.26 R[SUB]J[/SUB]) hot Jupiter in a 3.5 d period orbit around a metal-rich ([Fe/H][SUB]*[/SUB] = 0.33) star. WASP-147b and WASP-160Bb are promising targets for atmospheric characterization through transmission spectroscopy, while WASP-164b presents a good target for emission spectroscopy. [less ▲]

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See detailNGTS-4b: A sub-Neptune Transiting in the Desert
West, Richard G.; Gillen, Edward; Bayliss, Daniel et al

E-print/Working paper (2018)

We report the discovery of NGTS-4b, a sub-Neptune-sized planet transiting a 13th magnitude K-dwarf in a 1.34d orbit. NGTS-4b has a mass M=$20.6\pm3.0$M_E and radius R=$3.18\pm0.26$R_E, which places it ... [more ▼]

We report the discovery of NGTS-4b, a sub-Neptune-sized planet transiting a 13th magnitude K-dwarf in a 1.34d orbit. NGTS-4b has a mass M=$20.6\pm3.0$M_E and radius R=$3.18\pm0.26$R_E, which places it well within the so-called "Neptunian Desert". The mean density of the planet ($3.45\pm0.95$g/cm^3) is consistent with a composition of 100% H$_2$O or a rocky core with a volatile envelope. NGTS-4b is likely to suffer significant mass loss due to relatively strong EUV/X-ray irradiation. Its survival in the Neptunian desert may be due to an unusually high core mass, or it may have avoided the most intense X-ray irradiation by migrating after the initial activity of its host star had subsided. With a transit depth of $0.13\pm0.02$%, NGTS-4b represents the shallowest transiting system ever discovered from the ground, and is the smallest planet discovered in a wide-field ground-based photometric survey. [less ▲]

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See detailWASP-189b: an ultra-hot Jupiter transiting the bright A star HR 5599 in a polar orbit
Anderson, D. R.; Temple, L. Y.; Nielsen, L. D. et al

E-print/Working paper (2018)

We report the discovery of WASP-189b: an ultra-hot Jupiter in a 2.72-d transiting orbit around the $V = 6.6$ A star WASP-189 (HR 5599). We detected periodic dimmings in the star's lightcurve, first with ... [more ▼]

We report the discovery of WASP-189b: an ultra-hot Jupiter in a 2.72-d transiting orbit around the $V = 6.6$ A star WASP-189 (HR 5599). We detected periodic dimmings in the star's lightcurve, first with the WASP-South survey facility then with the TRAPPIST-South telescope. We confirmed that a planet is the cause of those dimmings via line-profile tomography and radial-velocity measurements using the HARPS and CORALIE spectrographs. Those reveal WASP-189b to be an ultra-hot Jupiter ($M_{\rm P}$ = 2.13 $\pm$ 0.28 $M_{\rm Jup}$; $R_{\rm P}$ = 1.374 $\pm$ 0.082 $R_{\rm Jup}$) in a polar orbit ($\lambda = 89.3 \pm 1.4^\circ$; $\Psi = 90.0 \pm 5.8^\circ$) around a rapidly rotating A6IV-V star ($T_{\rm eff}$ = 8000 $\pm$ 100 K; $v_* \sin i_*$ $\approx$ 100 km\, s$^{-1}$). We calculate a predicted equilibrium temperature of $T_{\rm eql}$ = 2641 $\pm$ 34 K, assuming zero albedo and efficient redistribution, which is the third hottest for the known exoplanets. WASP-189 is the brightest known host of a transiting hot Jupiter and the third-brightest known host of any transiting exoplanet. We note that of the eight hot-Jupiter systems with $T_{\rm eff}$ $>$ 7000 K, seven have strongly misaligned orbits, and two of the three systems with $T_{\rm eff}$ $\geq$ 8000 K have polar orbits (the third is aligned). [less ▲]

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See detailA low-density hot Jupiter in a near-aligned, 4.5-day orbit around a $V$ = 10.8, F5V star
Anderson, D. R.; Bouchy, F.; Brown, D. J. A. et al

E-print/Working paper (2018)

We report the independent discovery and characterisation of a hot Jupiter in a 4.5-d, transiting orbit around the star TYC 7282-1298-1 ($V$ = 10.8, F5V). The planet has been pursued by the NGTS team as ... [more ▼]

We report the independent discovery and characterisation of a hot Jupiter in a 4.5-d, transiting orbit around the star TYC 7282-1298-1 ($V$ = 10.8, F5V). The planet has been pursued by the NGTS team as NGTS-2b and by ourselves as WASP-179b. We characterised the system using a combination of photometry from WASP-South and TRAPPIST-South, and spectra from CORALIE (around the orbit) and HARPS (through the transit). We find the planet's orbit to be nearly aligned with its star's spin. From a detection of the Rossiter-McLaughlin effect, we measure a projected stellar obliquity of $\lambda = -19 \pm 6^\circ$. From line-profile tomography of the same spectra, we measure $\lambda = -11 \pm 5^\circ$. We find the planet to have a low density ($M_{\rm P}$ = 0.67 $\pm$ 0.09 $M_{\rm Jup}$, $R_{\rm P}$ = 1.54 $\pm$ 0.06 $R_{\rm Jup}$), which, along with its moderately bright host star, makes it a good target for transmission spectroscopy. We find a lower stellar mass ($M_*$ = $1.30 \pm 0.07$ $M_\odot$) than reported by the NGTS team ($M_*$ = $1.64 \pm 0.21$ $M_\odot$), though the difference is only $1.5$ $\sigma$. [less ▲]

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See detailOn the dust properties and dynamical evolution of the near- Earth Jupiter family comet 41P/Tuttle-Giacobini-Kresak
Pozuelos Romero, Francisco José ULiege; Jehin, Emmanuel ULiege; Moulane, Youssef et al

Poster (2018, September 01)

We present a study of the evolution of the dust environment of the near-Earth Jupiter family comet 41P/Tuttle-Giacobini-Kresak, based on observational data obtained using TRAPPIST telescopes from January ... [more ▼]

We present a study of the evolution of the dust environment of the near-Earth Jupiter family comet 41P/Tuttle-Giacobini-Kresak, based on observational data obtained using TRAPPIST telescopes from January to July, 2017. In addition, we performed numerical simulations to constrain its origin and dynamical nature. Along this work we compared our results with those obtained for 67P/Churyumov-Gerasimenko. These results have been recently accepted for publication in Astronomy & Astrophysics. [less ▲]

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See detailTRAPPIST monitoring of the activity and composition of the small near-Earth Jupiter Family Comets : 41P and 252P
Moulane, Youssef; Jehin, Emmanuel ULiege; José Pozuelos, Francisco et al

Poster (2018, September 01)

We monitored 41P and 252P on both sides of perihelion with the TRAPPIST telescopes. The gas species production rates were computed as well as the Afrho parameter for both comets. Our results have shown ... [more ▼]

We monitored 41P and 252P on both sides of perihelion with the TRAPPIST telescopes. The gas species production rates were computed as well as the Afrho parameter for both comets. Our results have shown that the two JFCs have a typical composition according to the Q(C2)/Q(CN) and Q(C3)/Q(CN) ratios but have a low gas and dust activity compared to other JFCs. We found that the activity of 41P is decreasing by about 30% to 40% from one apparition to the next. We confirmed rotation period derived from coma features slowed down by 20 hours in 2 months. 252P has shown an increase in production rates and dust production after perihelion which is believed to be associated with thermal processing of the nucleus surface. [less ▲]

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See detailWASP-128b: a transiting brown dwarf in the dynamical-tide regime
Hodžić, Vedad; Triaud, Amaury H. M. J.; Anderson, David R. et al

in Monthly Notices of the Royal Astronomical Society (2018)

Massive companions in close orbits around G dwarfs are thought to undergo rapid orbital decay due to runaway tidal dissipation. We report here the discovery of WASP-128b, a brown dwarf discovered by the ... [more ▼]

Massive companions in close orbits around G dwarfs are thought to undergo rapid orbital decay due to runaway tidal dissipation. We report here the discovery of WASP-128b, a brown dwarf discovered by the WASP survey transiting a G0V host on a 2.2 d orbit, where the measured stellar rotation rate places the companion in a regime where tidal interaction is dominated by dynamical tides. Under the assumption of dynamical equilibrium, we derive a value of the stellar tidal quality factor log {Q_\star ^' }} = {6.96 ± 0.19}. A combined analysis of ground-based photometry and high-resolution spectroscopy reveals a mass and radius of the host, M[SUB]⋆[/SUB] = 1.16 ± 0.04M[SUB]⊙[/SUB], R[SUB]⋆[/SUB] = 1.16 ± 0.02R[SUB]⊙[/SUB], and for the companion, M[SUB]b[/SUB] = 37.5 ± 0.8Mj, R[SUB]b[/SUB] = 0.94 ± 0.02Rj, placing WASP-128b in the driest parts of the brown dwarf desert, and suggesting a mild inflation for its age. We estimate a remaining lifetime for WASP-128b similar to that of some ultra-short period massive hot Jupiters, and note it may be a propitious candidate for measuring orbital decay and testing tidal theories. [less ▲]

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See detailA chemical survey of exoplanets with ARIEL
Tinetti, Giovanna; Drossart, Pierre; Eccleston, Paul et al

in Experimental Astronomy (2018)

Thousands of exoplanets have now been discovered with a huge range of masses, sizes and orbits: from rocky Earth-like planets to large gas giants grazing the surface of their host star. However, the ... [more ▼]

Thousands of exoplanets have now been discovered with a huge range of masses, sizes and orbits: from rocky Earth-like planets to large gas giants grazing the surface of their host star. However, the essential nature of these exoplanets remains largely mysterious: there is no known, discernible pattern linking the presence, size, or orbital parameters of a planet to the nature of its parent star. We have little idea whether the chemistry of a planet is linked to its formation environment, or whether the type of host star drives the physics and chemistry of the planet's birth, and evolution. ARIEL was conceived to observe a large number ( 1000) of transiting planets for statistical understanding, including gas giants, Neptunes, super-Earths and Earth-size planets around a range of host star types using transit spectroscopy in the 1.25-7.8 μm spectral range and multiple narrow-band photometry in the optical. ARIEL will focus on warm and hot planets to take advantage of their well-mixed atmospheres which should show minimal condensation and sequestration of high-Z materials compared to their colder Solar System siblings. Said warm and hot atmospheres are expected to be more representative of the planetary bulk composition. Observations of these warm/hot exoplanets, and in particular of their elemental composition (especially C, O, N, S, Si), will allow the understanding of the early stages of planetary and atmospheric formation during the nebular phase and the following few million years. ARIEL will thus provide a representative picture of the chemical nature of the exoplanets and relate this directly to the type and chemical environment of the host star. ARIEL is designed as a dedicated survey mission for combined-light spectroscopy, capable of observing a large and well-defined planet sample within its 4-year mission lifetime. Transit, eclipse and phase-curve spectroscopy methods, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, allow us to measure atmospheric signals from the planet at levels of 10-100 part per million (ppm) relative to the star and, given the bright nature of targets, also allows more sophisticated techniques, such as eclipse mapping, to give a deeper insight into the nature of the atmosphere. These types of observations require a stable payload and satellite platform with broad, instantaneous wavelength coverage to detect many molecular species, probe the thermal structure, identify clouds and monitor the stellar activity. The wavelength range proposed covers all the expected major atmospheric gases from e.g. H[SUB]2[/SUB]O, CO[SUB]2[/SUB], CH[SUB]4[/SUB] NH[SUB]3[/SUB], HCN, H[SUB]2[/SUB]S through to the more exotic metallic compounds, such as TiO, VO, and condensed species. Simulations of ARIEL performance in conducting exoplanet surveys have been performed - using conservative estimates of mission performance and a full model of all significant noise sources in the measurement - using a list of potential ARIEL targets that incorporates the latest available exoplanet statistics. The conclusion at the end of the Phase A study, is that ARIEL - in line with the stated mission objectives - will be able to observe about 1000 exoplanets depending on the details of the adopted survey strategy, thus confirming the feasibility of the main science objectives. [less ▲]

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See detailNon-detection of Contamination by Stellar Activity in the Spitzer Transit Light Curves of TRAPPIST-1
Morris, Brett M.; Agol, Eric; Hebb, Leslie et al

in Astrophysical Journal. Letters (2018), 863

We apply the transit light curve self-contamination technique of Morris et al. to search for the effect of stellar activity on the transits of the ultracool dwarf TRAPPIST-1 with 2018 Spitzer photometry ... [more ▼]

We apply the transit light curve self-contamination technique of Morris et al. to search for the effect of stellar activity on the transits of the ultracool dwarf TRAPPIST-1 with 2018 Spitzer photometry. The self-contamination method fits the transit light curves of planets orbiting spotted stars, allowing the host star to be a source of contaminating positive or negative flux that influences the transit depths but not the ingress/egress durations. We find that none of the planets show statistically significant evidence for self-contamination by bright or dark regions of the stellar photosphere. However, we show that small-scale magnetic activity, analogous in size to the smallest sunspots, could still be lurking undetected in the transit photometry. [less ▲]

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See detailDust modelling and dynamical study of comet 41P/Tuttle-Giacobini-Kresak during 2017 perihelion passage
Pozuelos Romero, Francisco José ULiege; Jehin, Emmanuel ULiege; Moulane, Youssef ULiege et al

in Astronomy and Astrophysics (2018), 615

Context. Thanks to the Rosetta mission, our understanding of comets has greatly improved. A very good opportunity to apply this knowledge appeared in early 2017 with the appearance of the Jupiter family ... [more ▼]

Context. Thanks to the Rosetta mission, our understanding of comets has greatly improved. A very good opportunity to apply this knowledge appeared in early 2017 with the appearance of the Jupiter family comet 41P/Tuttle-Giacobini-Kresak. The comet was only 0.15 au from the Earth as it passed through perihelion on April 12, 2017. We performed an observational campaign with the TRAPPIST telescopes that covered almost the entire period of time when the comet was active. Aims: In this work we present a comprehensive study of the evolution of the dust environment of 41P based on observational data from January to July, 2017. In addition, we performed numerical simulations to constrain its origin and dynamical nature. Methods: To model the observational data set we used a Monte Carlo dust tail model, which allowed us to derive the dust parameters that best describe its dust environment as a function of heliocentric distance: its dust production rate, the size distribution and ejection velocities of the dust particles, and its emission pattern. In order to study its dynamical evolution, we completed several experiments to evaluate the degree of stability of its orbit, its life time in its current region close to Earth, and its future behaviour. Results: From the dust analysis, we found that comet 41P is a dust-poor comet compared to other comets of the same family, with a complex emission pattern that shifted from full isotropic to anisotropic ejection sometime during February 24-March 14 in 2017, and then from anisotropic to full isotropic again between June 7 and 28. During the anisotropic period, the emission was controlled by two strongly active areas, where one was located in the southern and one in the northern hemisphere of the nucleus. The total dust mass loss is estimated to be 7.5 × 108 kg. From the dynamical simulations we estimate that 3600 yr is the period of time during which 41P will remain in a similar orbit. Taking into account the estimated mass loss per orbit, after 3600 yr, the nucleus may lose about 30% of its mass. However, based on its observed dust-to-water mass ratio and its propensity to outbursts, the lifetime of this comet could be much shorter. [less ▲]

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See detailKPS-1b: The First Transiting Exoplanet Discovered Using an Amateur Astronomerʼs Wide-field CCD Data
Burdanov, Artem ULiege; Gillon, Michaël ULiege

in Publications of the Astronomical Society of the Pacific (2018), 130(989),

We report the discovery of the transiting hot Jupiter KPS-1b. This exoplanet orbits a V=13.0 K1-type main-sequence star every 1.7~days, has a mass of 1.090 Mjup and a radius of 1.03 Rjup. The discovery ... [more ▼]

We report the discovery of the transiting hot Jupiter KPS-1b. This exoplanet orbits a V=13.0 K1-type main-sequence star every 1.7~days, has a mass of 1.090 Mjup and a radius of 1.03 Rjup. The discovery was made by the prototype Kourovka Planet Search (KPS) project, which used wide-field CCD data gathered by an amateur astronomer using readily available and relatively affordable equipment. Here we describe the equipment and observing technique used for the discovery of KPS-1b, its characterization with spectroscopic observations by the SOPHIE spectrograph and with high-precision photometry obtained with 1-m class telescopes. We also outline the KPS project evolution into the Galactic Plane eXoplanet survey (GPX). The discovery of KPS-1b represents a new major step of the contribution of amateur astronomers to the burgeoning field of exoplanetology. [less ▲]

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See detailModelling climate diversity, tidal dynamics and the fate of volatiles on TRAPPIST-1 planets
Turbet, Martin; Bolmont, Emeline; Leconte, Jeremy et al

in Astronomy and Astrophysics (2018), 612(86),

TRAPPIST-1 planets are invaluable for the study of comparative planetary science outside our Solar System and possibly habitability. First, we derive from N-body simulations possible planetary evolution ... [more ▼]

TRAPPIST-1 planets are invaluable for the study of comparative planetary science outside our Solar System and possibly habitability. First, we derive from N-body simulations possible planetary evolution scenarios, and show that each of the planets are likely to be in synchronous rotation. We then use a 3-D Global Climate Model to explore the possible climates of cool planets of the TRAPPIST-1 system. In particular, we look at the conditions required for cool planets to prevent possible volatile species to be lost by permanent condensation, irreversible burying or photochemical destruction. We also explore the resilience of the same volatiles (when in condensed phase) to a runaway greenhouse process. We find that background atmospheres made of N2, CO or O2 are resistant to atmospheric collapse. However, it should be difficult for TRAPPIST-1 planets to accumulate significant greenhouse gases like CO2, CH4, or NH3. CO2 can easily condense on the nightside, forming glaciers that would flow toward the substellar region. A complete CO2 ice cover is possible on TRAPPIST-1g and h only, although CO2 ice deposits could be gravitationally unstable and get buried beneath the water ice shell in geologically short timescales. Given TRAPPIST-1 planets large EUV irradiation (at least 1000x Titan's flux), CH4 and NH3 should be photodissociated rapidly and thus be hard to accumulate in the atmosphere. Photochemical hazes could then sedimentate and form a surface layer of tholins. Regarding habitability, we confirm that few bars of CO2 would suffice to warm the surface of TRAPPIST-1f and g above the melting point of water. We also show that TRAPPIST-1e is a remarkable candidate for surface habitability. If the planet is today synchronous and abundant in water, then it should always sustain surface liquid water at least in the substellar region, whatever the atmosphere considered. [less ▲]

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See detailIsotopic ratios in outbursting comet C/2015 ER61
Yang, Bin; Hutsemekers, Damien ULiege; Shinnaka, Yoshiharu et al

in Astronomy and Astrophysics (2018), 609

Isotopic ratios in comets are critical to understanding the origin of cometary material and the physical and chemical conditions in the early solar nebula. Comet C/2015 ER61 (PANSTARRS) underwent an ... [more ▼]

Isotopic ratios in comets are critical to understanding the origin of cometary material and the physical and chemical conditions in the early solar nebula. Comet C/2015 ER61 (PANSTARRS) underwent an outburst with a total brightness increase of 2 magnitudes on the night of 2017 April 4. The sharp increase in brightness offered a rare opportunity to measure the isotopic ratios of the light elements in the coma of this comet. We obtained two high-resolution spectra of C/2015 ER61 with UVES/VLT on the nights of 2017 April 13 and 17. At the time of our observations, the comet was fading gradually following the outburst. We measured the nitrogen and carbon isotopic ratios from the CN violet (0, 0) band and found that [SUP]12[/SUP]C/[SUP]13[/SUP]C = 100 ± 15, [SUP]14[/SUP]N/[SUP]15[/SUP]N = 130 ± 15. In addition, we determined the [SUP]14[/SUP]N/[SUP]15[/SUP]N ratio from four pairs of NH[SUB]2[/SUB] isotopolog lines and measured [SUP]14[/SUP]N/[SUP]15[/SUP]N = 140 ± 28. The measured isotopic ratios of C/2015 ER61 do not deviate significantly from those of other comets. [less ▲]

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See detailThe First Post-Kepler Brightness Dips of KIC 8462852
Boyajian, Tabetha S.; Alonso, Roi; Ammerman, Alex et al

in Astrophysical Journal. Letters (2018), 853(1), 14

We present a photometric detection of the first brightness dips of the unique variable star KIC 8462852 since the end of the Kepler space mission in 2013 May. Our regular photometric surveillance started ... [more ▼]

We present a photometric detection of the first brightness dips of the unique variable star KIC 8462852 since the end of the Kepler space mission in 2013 May. Our regular photometric surveillance started in 2015 October, and a sequence of dipping began in 2017 May continuing on through the end of 2017, when the star was no longer visible from Earth. We distinguish four main 1%-2.5% dips, named “Elsie,” “Celeste,” “Skara Brae,” and “Angkor,” which persist on timescales from several days to weeks. Our main results so far are as follows: (i) there are no apparent changes of the stellar spectrum or polarization during the dips and (ii) the multiband photometry of the dips shows differential reddening favoring non-gray extinction. Therefore, our data are inconsistent with dip models that invoke optically thick material, but rather they are in-line with predictions for an occulter consisting primarily of ordinary dust, where much of the material must be optically thin with a size scale ≪1 μm, and may also be consistent with models invoking variations intrinsic to the stellar photosphere. Notably, our data do not place constraints on the color of the longer-term “secular” dimming, which may be caused by independent processes, or probe different regimes of a single process. [less ▲]

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See detailThe First Post-Kepler Brightness Dips of KIC 8462852
Boyajian, Tabetha S.; Alonso, Roi; Ammerman, Alex et al

E-print/Working paper (2018)

We present a photometric detection of the first brightness dips of the unique variable star KIC 8462852 since the end of the Kepler space mission in 2013 May. Our regular photometric surveillance started ... [more ▼]

We present a photometric detection of the first brightness dips of the unique variable star KIC 8462852 since the end of the Kepler space mission in 2013 May. Our regular photometric surveillance started in October 2015, and a sequence of dipping began in 2017 May continuing on through the end of 2017, when the star was no longer visible from Earth. We distinguish four main 1-2.5% dips, named "Elsie," "Celeste," "Skara Brae," and "Angkor", which persist on timescales from several days to weeks. Our main results so far are: (i) there are no apparent changes of the stellar spectrum or polarization during the dips; (ii) the multiband photometry of the dips shows differential reddening favoring non-grey extinction. Therefore, our data are inconsistent with dip models that invoke optically thick material, but rather they are in-line with predictions for an occulter consisting primarily of ordinary dust, where much of the material must be optically thin with a size scale <<1um, and may also be consistent with models invoking variations intrinsic to the stellar photosphere. Notably, our data do not place constraints on the color of the longer-term "secular" dimming, which may be caused by independent processes, or probe different regimes of a single process. [less ▲]

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See detailStellar parameters for TRAPPIST-1
Van Grootel, Valérie ULiege; Silva Fernandes, Catarina ULiege; Gillon, Michaël ULiege et al

in Astrophysical Journal (2018), 853

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 ... [more ▼]

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 $\pm$ 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 $L_*=(5.22\pm0.19)\times 10^{-4} L_{\odot}$, very close to the previous estimate but almost twice 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 through 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 estimate for the effective temperature from our revised luminosity and radius. Our final results are $M_*=0.089 \pm 0.006 M_{\odot}$, $R_* = 0.121 \pm 0.003 R_{\odot}$, and $T_{\rm eff} =$ 2516 $\pm$ 41 K. Considering the degree to which 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. [less ▲]

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See detailThe discovery of WASP-151b, WASP-153b, WASP-156b: Insights on giant planet migration and the upper boundary of the Neptunian desert
Demangeon, O. D. S.; Faedi, F.; Hébrard, G. et al

in Astronomy and Astrophysics (2018), 610

To investigate the origin of the features discovered in the exoplanet population, the knowledge of exoplanets' mass and radius with a good precision (10%) is essential. To achieve this purpose the ... [more ▼]

To investigate the origin of the features discovered in the exoplanet population, the knowledge of exoplanets' mass and radius with a good precision (10%) is essential. To achieve this purpose the discovery of transiting exoplanets around bright stars is of prime interest. In this paper, we report the discovery of three transiting exoplanets by the SuperWASP survey and the SOPHIE spectrograph with mass and radius determined with a precision better than 15%. WASP-151b and WASP-153b are two hot Saturns with masses, radii, densities and equilibrium temperatures of 0.31-0.03 +0.04 MJ, 1.13-0.03 +0.03 RJ, 0.22-0.02 +0.03 ρJ and 1290-10 +20 K, and 0.39-0.02 +0.02 MJ, 1.55-0.08 +0.10 RJ, 0.11-0.02 +0.02 ρJ and 1700-40 +40 K, respectively. Their host stars are early G type stars (with mag V ~ 13) and their orbital periods are 4.53 and 3.33 days, respectively. WASP-156b is a super-Neptune orbiting a K type star (mag V = 11.6). It has a mass of 0.128-0.009 +0.010 MJ, a radius of 0.51-0.02 +0.02 RJ, a density of 1.0-0.1 +0.1 ρJ, an equilibrium temperature of 970-20 +30 K and an orbital period of 3.83 days. The radius of WASP-151b appears to be only slightly inflated, while WASP-153b presents a significant radius anomaly compared to a recently published model. WASP-156b, being one of the few well characterized super-Neptunes, will help to constrain the still debated formation of Neptune size planets and the transition between gas and ice giants. The estimates of the age of these three stars confirms an already observed tendency for some stars to have gyrochronological ages significantly lower than their isochronal ages. We propose that high eccentricity migration could partially explain this behavior for stars hosting a short period planet. Finally, these three planets also lie close to (WASP-151b and WASP-153b) or below (WASP-156b) the upper boundary of the Neptunian desert. Their characteristics support that the ultra-violet irradiation plays an important role in this depletion of planets observed in the exoplanet population. © 2018 ESO. [less ▲]

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See detailSPECULOOS Exoplanet Search and Its Prototype on TRAPPIST
Burdanov, Artem ULiege; Delrez, Laetitia; Gillon, Michaël ULiege et al

in Handbook of Exoplanets (2018)

One of the most significant goals of modern science is establishing whether life exists around other suns. The most direct path towards its achievement is the detection and atmospheric characterization of ... [more ▼]

One of the most significant goals of modern science is establishing whether life exists around other suns. The most direct path towards its achievement is the detection and atmospheric characterization of terrestrial exoplanets with potentially habitable surface conditions. The nearest ultracool dwarfs (UCDs), i.e., very-low-mass stars and brown dwarfs with effective temperatures lower than 2700 K, represent a unique opportunity to reach this goal within the next decade. The potential of the transit method for detecting potentially habitable Earth-sized planets around these objects is drastically increased compared to Earth-Sun analogs. A terrestrial planet transiting a nearby UCD could be an exquisite target for a thorough atmospheric characterization, including the search for possible biosignatures, with near-future facilities such as the James Webb Space Telescope. In this chapter, we first describe the physical properties of UCDs as well as the unique potential they offer for the detection of potentially habitable Earth-sized planets suitable for atmospheric characterization. Then, we present the SPECULOOS ground-based transit survey, that will search for Earth-sized planets transiting the nearest UCDs, as well as its prototype survey on the TRAPPIST telescopes. We conclude by discussing the prospects offered by the recent detection by this prototype survey of a system of seven temperate Earth-sized planets transiting a nearby UCD, TRAPPIST-1. [less ▲]

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See detailEarly 2017 observations of TRAPPIST-1 with Spitzer
Delrez, L.; Gillon, Michaël ULiege; Triaud, A. H. M. J. et al

in Monthly Notices of the Royal Astronomical Society (2018), 475(3), 3577-3597

The recently detected TRAPPIST-1 planetary system, with its seven planets transiting a nearby ultracool dwarf star, offers the first opportunity to perform comparative exoplanetology of temperate Earth ... [more ▼]

The recently detected TRAPPIST-1 planetary system, with its seven planets transiting a nearby ultracool dwarf star, offers the first opportunity to perform comparative exoplanetology of temperate Earth-sized worlds. To further advance our understanding of these planets' compositions, energy budgets, and dynamics, we are carrying out an intensive photometric monitoring campaign of their transits with the Spitzer Space Telescope. In this context, we present 60 new transits of the TRAPPIST-1 planets observed with Spitzer/Infrared Array Camera (IRAC) in 2017 February and March. We combine these observations with previously published Spitzer transit photometry and perform a global analysis of the resulting extensive data set. This analysis refines the transit parameters and provides revised values for the planets' physical parameters, notably their radii, using updated properties for the star. As part of our study, we also measure precise transit timings that will be used in a companion paper to refine the planets' masses and compositions using the transit timing variations method. TRAPPIST-1 shows a very low level of low-frequency variability in the IRAC 4.5-μmband, with a photometric RMS of only 0.11 per cent at a 123-s cadence. We do not detect any evidence of a (quasi-)periodic signal related to stellar rotation. We also analyse the transit light curves individually, to search for possible variations in the transit parameters of each planet due to stellar variability, and find that the Spitzer transits of the planets are mostly immune to the effects of stellar variations. These results are encouraging for forthcoming transmission spectroscopy observations of the TRAPPIST-1 planets with the James Webb Space Telescope. © 2018 The Author(s). [less ▲]

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See detailUnmasking the hidden NGTS-3Ab: A hot Jupiter in an unresolved binary system
Günther, M. N.; Queloz, D.; Gillen, E. et al

in Monthly Notices of the Royal Astronomical Society (2018), 478(4), 4720-4737

We present the discovery of NGTS-3Ab, a hot Jupiter found transiting the primary star of an unresolved binary system. We develop a joint analysis of multicolour photometry, centroids, radial velocity (RV ... [more ▼]

We present the discovery of NGTS-3Ab, a hot Jupiter found transiting the primary star of an unresolved binary system. We develop a joint analysis of multicolour photometry, centroids, radial velocity (RV) cross-correlation function (CCF) profiles, and their bisector inverse slopes (BIS) to disentangle this three-body system. Data from the Next Generation Transit Survey (NGTS), SPECULOOS and HARPS are analysed and modelled with our new BLENDFITTER software. We find that the binary consists of NGTS-3A (G6V-dwarf) and NGTS-3B (K1Vdwarf) at < 1 arcsec separation. NGTS-3Ab orbits every 1.675 d. The planet radius and mass are Rplanet = 1.48 ± 0.37 RJ and Mplanet = 2.38 ± 0.26MJ, suggesting it is potentially inflated. We emphasize that only combining all the information frommulticolour photometry, centroids and RV CCF profiles can resolve systems like NGTS-3. Such systems cannot be disentangled from single-colour photometry and RV measurements alone. Importantly, the presence of a BIS correlation indicates a blend scenario, but is not sufficient to determine which star is orbited by the third body. Moreover, even if no BIS correlation is detected, a blend scenario cannot be ruled out without further information. The choice of methodology for calculating the BIS can influence the measured significance of its correlation. The presented findings are crucial to consider for wide-field transit surveys, which require wide CCD pixels (> 5 arcsec) and are prone to contamination by blended objects. With TESS on the horizon, it is pivotal for the candidate vetting to incorporate all available follow-up information from multicolour photometry and RV CCF profiles. © 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. [less ▲]

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