Ground-based simultaneous multiband transit observations allow an accurate system parameters determination and may lead to the detection and characterization of additional bodies via the transit ...timing variations (TTVs) method. We aimed to (i) characterize the heavily bloated WASP-4b hot Jupiter and its star by measuring system parameters and the dependence of the planetary radius as a function of four (Sloan g', r', i', z') wavelengths and (ii) search for TTVs. We recorded 987 images during three complete transits with the GROND instrument, mounted on the MPG/ESO-2.2m telescope at La Silla Observatory. Assuming a quadratic law for the stellar limb darkening we derive system parameters by fitting a composite transit light curve over all bandpasses simultaneously. To compute uncertainties of the fitted parameters, we employ the Bootstrap Monte Carlo Method. The three central transit times are measured with precision down to 6 s. We find a planetary radius Rp = 1.413+/-0.020 RJup, an orbital inclination i = 88deg57'+/-0.45deg and calculate a new ephemeris, a period P = 1.33823144+/-0.00000032days and a reference transit epoch T0 = 2454697.798311+/-0.000046 (BJD). Analysis of the new transit mid-times in combination with previous measurements shows no sign of a TTV signal greater than 20s. We perform simplified numerical simulations to place upper-mass limits of a hypothetical perturber in the WASP-4b system.
Exoplanets transiting bright nearby stars are key objects for advancing our knowledge of planetary formation and evolution. The wealth of photons from the host star gives detailed access to the ...atmospheric, interior, and orbital properties of the planetary companions. \(\nu^2\) Lupi (HD 136352) is a naked-eye (\(V = 5.78\)) Sun-like star that was discovered to host three low-mass planets with orbital periods of 11.6, 27.6, and 107.6 days via radial velocity monitoring (Udry et al. 2019). The two inner planets (b and c) were recently found to transit (Kane et al. 2020), prompting a photometric follow-up by the brand-new \(CHaracterising\:ExOPlanets\:Satellite\:(CHEOPS)\). Here, we report that the outer planet d is also transiting, and measure its radius and mass to be \(2.56\pm0.09\) \(R_{\oplus}\) and \(8.82\pm0.94\) \(M_{\oplus}\), respectively. With its bright Sun-like star, long period, and mild irradiation (\(\sim\)5.7 times the irradiation of Earth), \(\nu^2\) Lupi d unlocks a completely new region in the parameter space of exoplanets amenable to detailed characterization. We refine the properties of all three planets: planet b likely has a rocky mostly dry composition, while planets c and d seem to have retained small hydrogen-helium envelopes and a possibly large water fraction. This diversity of planetary compositions makes the \(\nu^2\) Lupi system an excellent laboratory for testing formation and evolution models of low-mass planets.
The T Tauri star PTFO 8-8695 exhibits periodic fading events that have been interpreted as the transits of a giant planet on a precessing orbit. Here we present three tests of the planet hypothesis. ...First, we sought evidence for the secular changes in light-curve morphology that are predicted to be a consequence of orbital precession. We observed 28 fading events spread over several years, and did not see the expected changes. Instead we found that the fading events are not strictly periodic. Second, we attempted to detect the planet's radiation, based on infrared observations spanning the predicted times of occultations. We ruled out a signal of the expected amplitude. Third, we attempted to detect the Rossiter-McLaughlin effect by performing high-resolution spectroscopy throughout a fading event. No effect was seen at the expected level, ruling out most (but not all) possible orientations for the hypothetical planetary orbit. Our spectroscopy also revealed strong, time-variable, high-velocity H{\alpha} and Ca H & K emission features. All these observations cast doubt on the planetary hypothesis, and suggest instead that the fading events represent starspots, eclipses by circumstellar dust, or occultations of an accretion hotspot.
WASP-80b is a missing link in the study of exo-atmospheres. It falls between the warm Neptunes and the hot Jupiters and is amenable for characterisation, thanks to its host star's properties. We ...observed the planet through transit and during occultation with Warm Spitzer. Combining our mid-infrared transits with optical time series, we find that the planet presents a transmission spectrum indistinguishable from a horizontal line. In emission, WASP-80b is the intrinsically faintest planet whose dayside flux has been detected in both the 3.6 and 4.5 \(\mu\)m Spitzer channels. The depths of the occultations reveal that WASP-80b is as bright and as red as a T4 dwarf, but that its temperature is cooler. If planets go through the equivalent of an L-T transition, our results would imply this happens at cooler temperatures than for brown dwarfs. Placing WASP-80b's dayside into a colour-magnitude diagram, it falls exactly at the junction between a blackbody model and the T-dwarf sequence; we cannot discern which of those two interpretations is the more likely. Flux measurements on other planets with similar equilibrium temperatures are required to establish whether irradiated gas giants, like brown dwarfs, transition between two spectral classes. An eventual detection of methane absorption in transmission would also help lift that degeneracy. We obtained a second series of high-resolution spectra during transit, using HARPS. We reanalyse the Rossiter-McLaughlin effect. The data now favour an aligned orbital solution and a stellar rotation nearly three times slower than stellar line broadening implies. A contribution to stellar line broadening, maybe macroturbulence, is likely to have been underestimated for cool stars, whose rotations have therefore been systematically overestimated. abridged
We present the discovery of CoRoT 223992193, a double-lined, detached eclipsing binary, comprising two pre-main sequence M dwarfs, discovered by the CoRoT space mission during a 23-day observation of ...the 3 Myr old NGC 2264 star-forming region. Using multi-epoch optical and near-IR follow-up spectroscopy with FLAMES on the Very Large Telescope and ISIS on the William Herschel Telescope we obtain a full orbital solution and derive the fundamental parameters of both stars by modelling the light curve and radial velocity data. The orbit is circular and has a period of \(3.8745745 \pm 0.0000014\) days. The masses and radii of the two stars are \(0.67 \pm 0.01\) and \(0.495 \pm 0.007\) \(M_{\odot}\) and \(1.30 \pm 0.04\) and \(1.11 ~^{+0.04}_{-0.05}\) \(R_{\odot}\), respectively. This system is a useful test of evolutionary models of young low-mass stars, as it lies in a region of parameter space where observational constraints are scarce; comparison with these models indicates an apparent age of \(\sim\)3.5-6 Myr. The systemic velocity is within \(1\sigma\) of the cluster value which, along with the presence of lithium absorption, strongly indicates cluster membership. The CoRoT light curve also contains large-amplitude, rapidly evolving out-of-eclipse variations, which are difficult to explain using starspots alone. The system's spectral energy distribution reveals a mid-infrared excess, which we model as thermal emission from a small amount of dust located in the inner cavity of a circumbinary disk. In turn, this opens up the possibility that some of the out-of-eclipse variability could be due to occultations of the central stars by material located at the inner edge or in the central cavity of the circumbinary disk.
Exoplanetary science has reached a historic moment. The James Webb Space Telescope will be capable of probing the atmospheres of rocky planets, and perhaps even search for biologically produced ...gases. However this is contingent on identifying suitable targets before the end of the mission. A race therefore, is on, to find transiting planets with the most favorable properties, in time for the launch. Here, we describe a realistic opportunity to discover extremely favorable targets - rocky planets transiting nearby brown dwarfs - using the Spitzer Space Telescope as a survey instrument. Harnessing the continuous time coverage and the exquisite precision of Spitzer in a 5,400 hour campaign monitoring nearby brown dwarfs, we will detect a handful of planetary systems with planets as small as Mars. The survey we envision is a logical extension of the immense progress that has been realized in the field of exoplanets and a natural outcome of the exploration of the solar neighborhood to map where the nearest habitable rocky planets are located (as advocated by the 2010 Decadal Survey). Our program represents an essential step towards the atmospheric characterization of terrestrial planets and carries the compelling promise of studying the concept of habitability beyond Earth-like conditions. In addition, our photometric monitoring will provide invaluable observations of a large sample of nearby brown dwarfs situated close to the M/L transition. This is why, we also advocate an immediate public release of the survey data, to guarantee rapid progress on the planet search and provide a treasure trove of data for brown dwarf science.
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