ABSTRACT Exploiting the Kepler transit data, we uncover a dramatic distinction in the prevalence of sub-Jovian companions between systems that contain hot Jupiters (HJs) (periods inward of 10 days) ...and those that host warm Jupiters (WJs) (periods between 10 and 200 days). HJs, with the singular exception of WASP-47b, do not have any detectable inner or outer planetary companions (with periods inward of 50 days and sizes down to 2 REarth). Restricting ourselves to inner companions, our limits reach down to 1 REarth. In stark contrast, half of the WJs are closely flanked by small companions. Statistically, the companion fractions for hot and WJs are mutually exclusive, particularly in regard to inner companions. The high companion fraction of WJs also yields clues to their formation. The WJs that have close-by siblings should have low orbital eccentricities and low mutual inclinations. The orbital configurations of these systems are reminiscent of those of the low-mass close-in planetary systems abundantly discovered by the Kepler mission. This, and other arguments, lead us to propose that these WJs are formed in situ. There are indications that there may be a second population of WJs with different characteristics. In this picture, WASP-47b could be regarded as the extending tail of the in situ WJs into the HJ region and does not represent the generic formation route for HJs.
Star-like objects with effective temperatures of less than 2,700 kelvin are referred to as 'ultracool dwarfs'. This heterogeneous group includes stars of extremely low mass as well as brown dwarfs ...(substellar objects not massive enough to sustain hydrogen fusion), and represents about 15 per cent of the population of astronomical objects near the Sun. Core-accretion theory predicts that, given the small masses of these ultracool dwarfs, and the small sizes of their protoplanetary disks, there should be a large but hitherto undetected population of terrestrial planets orbiting them--ranging from metal-rich Mercury-sized planets to more hospitable volatile-rich Earth-sized planets. Here we report observations of three short-period Earth-sized planets transiting an ultracool dwarf star only 12 parsecs away. The inner two planets receive four times and two times the irradiation of Earth, respectively, placing them close to the inner edge of the habitable zone of the star. Our data suggest that 11 orbits remain possible for the third planet, the most likely resulting in irradiation significantly less than that received by Earth. The infrared brightness of the host star, combined with its Jupiter-like size, offers the possibility of thoroughly characterizing the components of this nearby planetary system.
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.
Three Earth-sized exoplanets were recently discovered close to the habitable zone of the nearby ultracool dwarf star TRAPPIST-1 (ref. 3). The nature of these planets has yet to be determined, as ...their masses remain unmeasured and no observational constraint is available for the planetary population surrounding ultracool dwarfs, of which the TRAPPIST-1 planets are the first transiting example. Theoretical predictions span the entire atmospheric range, from depleted to extended hydrogen-dominated atmospheres. Here we report observations of the combined transmission spectrum of the two inner planets during their simultaneous transits on 4 May 2016. The lack of features in the combined spectrum rules out cloud-free hydrogen-dominated atmospheres for each planet at ≥10σ levels; TRAPPIST-1 b and c are therefore unlikely to have an extended gas envelope as they occupy a region of parameter space in which high-altitude cloud/haze formation is not expected to be significant for hydrogen-dominated atmospheres. Many denser atmospheres remain consistent with the featureless transmission spectrum-from a cloud-free water-vapour atmosphere to a Venus-like one.
The TRAPPIST-1 system is unique in that it has a chain of seven terrestrial Earth-like planets located close to or in its habitable zone. In this paper, we study the effect of potential cometary ...impacts on the TRAPPIST-1 planets and how they would affect the primordial atmospheres of these planets. We consider both atmospheric mass loss and volatile delivery with a view to assessing whether any sort of life has a chance to develop. We ran N-body simulations to investigate the orbital evolution of potential impacting comets, to determine which planets are more likely to be impacted and the distributions of impact velocities. We consider three scenarios that could potentially throw comets into the inner region (i.e. within 0.1 au where the seven planets are located) from an (as yet undetected) outer belt similar to the Kuiper belt or an Oort cloud: planet scattering, the Kozai–Lidov mechanism, and Galactic tides. For the different scenarios, we quantify, for each planet, how much atmospheric mass is lost and what mass of volatiles can be delivered over the age of the system depending on the mass scattered out of the outer belt. We find that the resulting high-velocity impacts can easily destroy the primordial atmospheres of all seven planets, even if the mass scattered from the outer belt is as low as that of the Kuiper belt. However, we find that the atmospheres of the outermost planets f, g, and h can also easily be replenished with cometary volatiles (e.g. ∼ an Earth ocean mass of water could be delivered). These scenarios would thus imply that the atmospheres of these outermost planets could be more massive than those of the innermost planets, and have volatiles-enriched composition.
Transits on single stars are rare. The probability rarely exceeds a few per cent. Furthermore, this probability rapidly approaches zero at increasing orbital period. Therefore, transit surveys have ...been predominantly limited to the inner parts of exoplanetary systems. Here, we demonstrate how circumbinary planets allow us to beat these unfavourable odds. By incorporating the geometry and the three-body dynamics of circumbinary systems, we analytically derive the probability of transitability, a configuration where the binary and planet orbits overlap on the sky. We later show that this is equivalent to the transit probability, but at an unspecified point in time. This probability, at its minimum, is always higher than for single star cases. In addition, it is an increasing function with mutual inclination. By applying our analytical development to eclipsing binaries, we deduce that transits are highly probable, and in some case guaranteed. For example, a circumbinary planet revolving at 1 au around a 0.3 au eclipsing binary is certain to eventually transit – a 100 per cent probability – if its mutual inclination is greater than 0
$_{.}^{\circ}$
6. We show that the transit probability is generally only a weak function of the planet's orbital period; circumbinary planets may be used as practical tools for probing the outer regions of exoplanetary systems to search for and detect warm to cold transiting planets.
ABSTRACT
Colour–magnitude diagrams provide a convenient way of comparing populations of similar objects. When well populated with precise measurements, they allow quick inferences to be made about ...the bulk properties of an astronomic object simply from its proximity on a diagram to other objects. We present here a python toolkit that allows a user to produce colour–magnitude diagrams of transiting exoplanets, comparing planets to populations of ultra-cool dwarfs, of directly imaged exoplanets, to theoretical models of planetary atmospheres, and to other transiting exoplanets. Using a selection of near- and mid-infrared colour–magnitude diagrams, we show how outliers can be identified for further investigation, and how emerging subpopulations can be identified. Additionally, we present evidence that observed differences in the Spitzer’s 4.5 μm flux, between irradiated Jupiters and field brown dwarfs, might be attributed to phosphine, which is susceptible to photolysis. The presence of phosphine in low-irradiation environments may negate the need for thermal inversions to explain eclipse measurements. We speculate that the anomalously low 4.5 μm flux of the nightside of HD 189733b and the daysides of GJ 436b and GJ 3470b might be caused by phosphine absorption. Finally, we use our toolkit to include Hubble Wide Field Camera 3 spectra, creating a new photometric band called the ‘Water band’ (WJH band) in the process. We show that the colour index WJH − H can be used to constrain the C/O ratio of exoplanets, showing that future observations with James Webb Space Telescope and Ariel will be able to distinguish these populations if they exist, and select members for future follow-up.
ABSTRACT
Advances in high-precision spectrographs have paved the way for the search for an Earth analogue orbiting a Sun-like star within its habitable zone. However, the research community remains ...limited by the presence of stellar noise produced by stellar magnetic activity. These activity phenomena can obscure the detection of Earth-mass exoplanets and can create parasitic signals in transmission spectra. In this paper, we outline the need for a public forecast of stellar activity and produce a proof of principle. Using publicly available spectra we are able to forecast stellar minima several years ahead and reach a typical uncertainty on the timing of these minima of $\pm 0.5~\rm yr$, similar to the precision reached on our own Sun’s magnetic cycle. Furthermore, we use our toy model to show that knowing when to observe can improve the sensitivity of HARPS-North’s Solar telescope to low-mass planets by up to an order of magnitude, and we show that the majority of exoplanets selected for Early Release Science and Guaranteed Time Observations on the James Webb will be observed close or during stellar maxima, incurring a higher risk of stellar contamination. We finish our paper by outlining a number of next steps to create a public forecast usable by teams around the globe, by telescope time allocation committees, and in preparation for spacecraft such as Ariel.
ABSTRACT
Planet–planet scattering events can leave an observable trace of a planet’s migration history in the form of orbital misalignment with respect to the stellar spin axis, which is measurable ...from spectroscopic time-series taken during transit. We present high-resolution spectroscopic transits observed with ESPRESSO of the close-in super-Earth π Men c. The system also contains an outer giant planet on a wide, eccentric orbit, recently found to be inclined with respect to the inner planetary orbit. These characteristics are reminiscent of past dynamical interactions. We successfully retrieve the planet-occulted light during transit, and find evidence that the orbit of π Men c is moderately misaligned with the stellar spin axis with λ = − 24${_{.}^{\circ}}$0 ± 4${_{.}^{\circ}}$1 ($\psi = {26{_{.}^{\circ}} 9}^{+5{_{.}^{\circ}}8 }_{-4{_{.}^{\circ}}7 }$). This is consistent with the super-Earth π Men c having followed a high-eccentricity migration followed by tidal circularization, and hints that super-Earths can form at large distances from their star. We also detect clear signatures of solar-like oscillations within our ESPRESSO radial velocity time series, where we reach a radial velocity precision of ∼20 cm s−1. We model the oscillations using Gaussian processes (GPs) and retrieve a frequency of maximum oscillation, $\nu _\mathrm{max}{} = 2771^{+65}_{-60}\, \mu \mathrm{Hz}$. These oscillations make it challenging to detect the Rossiter–McLaughlin effect using traditional methods. We are, however, successful using the reloaded Rossiter–McLaughlin approach. Finally, in the appendix, we also present physical parameters and ephemerides for π Men c from a GP transit analysis of the full Transiting Exoplanet Survey Satellite Cycle 1 data.
Stellar Parameters for Trappist-1 Grootel, Valérie Van; Fernandes, Catarina S.; Gillon, Michael ...
The Astrophysical journal,
01/2018, Letnik:
853, Številka:
1
Journal Article, Web Resource
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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 , 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 , , and 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.
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