We present 197 planet candidates discovered using data from the first year of the NASA K2 mission (Campaigns 0-4), along with the results of an intensive program of photometric analyses, stellar spectroscopy, high-resolution imaging, and statistical validation. We distill these candidates into sets of 104 validated planets (57 in multi-planet systems), 30 false positives, and 63 remaining candidates. Our validated systems span a range of properties, with median values of R P = 2.3 R ⊕ , P = 8.6 d, T eff = 5300 K, and Kp = 12.7 mag. Stellar spectroscopy provides precise stellar and planetary parameters for most of these systems. We show that K2 has increased by 30% the number of small planets known to orbit moderately bright stars (1-4 R ⊕ , Kp = 9-13 mag). Of particular interest are 37 planets smaller than 2 R ⊕ , 15 orbiting stars brighter than Kp = 11.5 mag, five receiving Earth-like irradiation levels, and several multi-planet systems -including four planets orbiting the M dwarf K2-72 near mean-motion resonances. By quantifying the likelihood that each candidate is a planet we demonstrate that our candidate sample has an overall false positive rate of 15 − 30%, with rates substantially lower for small candidates (< 2R ⊕ ) and larger for candidates with radii > 8R ⊕ and/or with P < 3 d. Extrapolation of the current planetary yield suggests that K2 will discover between 500 − 1000 planets in its planned four-year mission -assuming sufficient follow-up resources are available. Efficient observing and analysis, together with an organized and coherent follow-up strategy, is essential to maximize the efficacy of planet-validation efforts for K2 , TESS , and future large-scale surveys. 1 We distinguish "confirmed" systems (with measured masses) from "validated" systems (whose planetary nature has been statistically demonstrated, e.g. with false positive probability < 1% ).

Since 2014, NASA's K2 mission has observed large portions of the ecliptic plane in search of transiting planets and has detected hundreds of planet candidates. With observations planned until at least early 2018, K2 will continue to identify more planet candidates. We present here 275 planet candidates observed during Campaigns 0-10 of the K2 mission that are orbiting stars brighter than 13 mag (in Kepler band) and for which we have obtained highresolution spectra (R = 44,000). These candidates are analyzed using the vespa package in order to calculate their false-positive probabilities (FPP). We find that 149 candidates are validated with an FPP lower than 0.1%, 39 of which were previously only candidates and 56 of which were previously undetected. The processes of data reduction, candidate identification, and statistical validation are described, and the demographics of the candidates and newly validated planets are explored. We show tentative evidence of a gap in the planet radius distribution of our candidate sample. Comparing our sample to the Kepler candidate sample investigated by Fulton et al., we conclude that more planets are required to quantitatively confirm the gap with K2 candidates or validated planets. This work, in addition to increasing the population of validated K2 planets by nearly 50% and providing new targets for follow-up observations, will also serve as a framework for validating candidates from upcoming K2 campaigns and the Transiting Exoplanet Survey Satellite, expected to launch in 2018.

Brown dwarfs -interstellar bodies more massive than planets but not massive enough to initiate the sustained hydrogen fusion that powers self-luminous stars 1,2 -are born hot and slowly cool as they age. As they cool below ~2300 K, liquid or crystalline particles composed of calcium aluminates, silicates, and/or iron condense into atmospheric "dust" 3,4 which disappears at still cooler temperatures (~1300 K) 5,6 . Models to explain this dust dispersal include both an abrupt sinking of the entire cloud deck into the deep, unobservable atmosphere 5,7 or breakup of the cloud into scattered patches 6,8 (as seen on Jupiter and Saturn 9 ), but to date observations of brown dwarfs have been limited to globally integrated measurements 10 ; such measurements can reveal surface inhomogeneities but cannot unambiguously resolve surface features 11 . Here we report a twodimensional map of a brown dwarf's surface that allows identification of large-scale bright and dark features, indicative of patchy clouds. Geographic localization of such features, and the ability to create timelapsed extrasolar weather movies in the near future, provide important new constraints on the formation, evolution, and dispersal of clouds in brown dwarf and extrasolar planet atmospheres.The recent discovery of the Luhman 16AB system (also called WISE J104915.57-531906.1AB; Ref. 12) revealed two brown dwarfs only 2 parsecs away, making these the closest objects to the Solar system after the alpha Centauri system and Barnard's star. Both of these newly-discovered brown dwarfs are near the dust clearing temperature 13,14 , and one (Luhman 16B) exhibits strong temporal variability of its thermal radiation consistent with a rotation period of 4.9 hr 15. Luhman 16AB's proximity to Earth makes these the first substellar objects bright enough to be studied at high precision and high spectral resolution on short timescales, so we observed both of these brown dwarfs for five hours (one rotation period of Luhman 16B) using the CRIRES spectrograph 16 at ESO's Very Large Telescope to search for spectroscopic variability. of 17Absorption features from CO and H2O dominate the brown dwarfs' spectra, as shown in Fig. 1. The two objects have similar spectra but the absorption lines are broader for the B component: it exhibits a projected equatorial rotational velocity of 26.1 +/-0.2 km/s, vs. 17.6 +/-0.1 km/s for Luhman 16A. Taking Luhman 16B's rotation period 15 and considering that evolutionary models predict these objects to be 1.0+/-0.2 times the radius of Jupiter 17 , Luhman 16B's rotation axis must be inclined ≲30 deg from the plane of the sky; i.e., we are viewing this brown dwarf nearly equator-on. If the two brown dwarfs' axes are closely aligned (like those of the planets in our Solar system) then Luhman 16A rotates more slowly than Luhman 16B and the objects either formed with different initial angular momentum or experienced different accretion or spin-braking histories. Alternatively, if the two brown dwarfs have comparable rotation periods (as tentativ...

Small, cool planets represent the typical end-products of planetary formation. Studying the architectures of these systems, measuring planet masses and radii, and observing these planets' atmospheres during transit directly informs theories of planet assembly, migration, and evolution. Here we report the discovery of three small planets orbiting a bright (K s = 8.6 mag) M0 dwarf using data collected as part of K2, the new ecliptic survey using the re-purposed Kepler spacecraft. Stellar spectroscopy and K2 photometry indicate that the system hosts three transiting planets with radii 1.5 -2.1 R ⊕ , straddling the transition region between rocky and increasingly volatile-dominated compositions. With orbital periods of 10-45 days the planets receive just 1.5-10× the flux incident on Earth, making these some of the coolest small planets known orbiting a nearby star; planet d is located near the inner edge of the system's habitable zone. The bright, low-mass star makes this system an excellent laboratory to determine the planets' masses via Doppler spectroscopy and to constrain their atmospheric compositions via transit spectroscopy. This discovery demonstrates the ability of K2 and future space-based transit searches to find many fascinating objects of interest.

We present 2241 exoplanet candidates identified with data from the Transiting Exoplanet Survey Satellite (TESS) during its 2 yr Prime Mission. We list these candidates in the TESS Objects of Interest (TOI) Catalog, which includes both new planet candidates found by TESS and previously known planets recovered by TESS observations. We describe the process used to identify TOIs, investigate the characteristics of the new planet candidates, and discuss some notable TESS planet discoveries. The TOI catalog includes an unprecedented number of small planet candidates around nearby bright stars, which are well suited for detailed follow-up observations. The TESS data products for the Prime Mission (sectors 1-26), including the TOI catalog, light curves, full-frame images, and target pixel files, are publicly available at the Mikulski Archive for Space Telescopes.

Context. HR 4796 A is surrounded by a debris disc, observed in scattered light as an inclined ring with a high surface brightness. Past observations have raised several questions. First, a strong brightness asymmetry detected in polarised reflected light has recently challenged our understanding of scattering by the dust particles in this system. Secondly, the morphology of the ring strongly suggests the presence of planets, although no planets have been detected to date. Aims. We aim here at measuring with high accuracy the morphology and photometry of the ring in scattered light, in order to derive the phase function of the dust and constrain its near-infrared spectral properties. We also want to constrain the presence of planets and set improved constraints on the origin of the observed ring morphology. Methods. We obtained high-angular resolution coronagraphic images of the circumstellar environment around HR 4796 A with VLT/SPHERE during the commissioning of the instrument in May 2014 and during guaranteed-time observations in February 2015. The observations reveal for the first time the entire ring of dust, including the semi-minor axis that was previously hidden either behind the coronagraphic spot or in the speckle noise. Results. We determine empirically the scattering phase function of the dust in the H band from 13.6 • to 166.6 •. It shows a prominent peak of forward scattering, never detected before, for scattering angles below 30 •. We analyse the reflectance spectra of the disc from the 0.95 µm to 1.6 µm, confirming the red colour of the dust, and derive detection limits on the presence of planetary mass objects. Conclusions. We confirm which side of the disc is inclined towards the Earth. The analysis of the phase function, especially below 45 • , suggests that the dust population is dominated by particles much larger than the observation wavelength, of about 20 µm. Compact Mie grains of this size are incompatible with the spectral energy distribution of the disc, however the observed rise in scattering efficiency beyond 50 • points towards aggregates which could reconcile both observables. We do not detect companions orbiting the star, but our high-contrast observations provide the most stringent constraints yet on the presence of planets responsible for the morphology of the dust.

Theories of the formation and early evolution of planetary systems postulate that planets are born in circumstellar disks, and undergo radial migration during and after dissipation of the dust and gas disk from which they formed 1,2 . The precise ages of meteorites indicate that planetesimals -the building blocks of planets -are produced within the first million years of a star's life 3 . A prominent question is: how early can one find fully formed planets like those frequently detected on short orbital periods around mature stars? Some theories suggest the in situ formation of planets close to their host stars is unlikely and the existence of such planets is evidence for large scale migration 4,5 . Other theories posit that planet assembly at small orbital separations may be common [6][7][8] . Here we report on a newly-born, transiting planet orbiting its star every 5.4 days. The planet is 50% larger than Neptune, and its mass is less than 3.6 times Jupiter (at 99.7% confidence), with a true mass likely to be within a factor of several of Neptune's. The 5-10 million year old star has a tenuous dust disk extending in to about 2 times the Earth-Sun separation, in addition to the large planet located at less than 1/20 the Earth-Sun separation.USco 161014. 75-191909.3, hereafter K2-33, is a several million year old M-type star that was observed by NASA's Kepler Space Telescope during Campaign 2 of the K2 mission. The star was identified as one of more than 200 candidate planet hosts in a systematic search for transits in K2 data 9 . As part of our ongoing study of the pre-main sequence population of Upper Scorpius observed by K2, we independently verified and analyzed the planetary transit signal. We acquired radial velocity (RV) and high spatial resolution observations at the W. M. Keck Observatory to confirm the planet, hereafter K2-33b, and to measure its size and mass.2 Within the 77.5 day photometric time series of K2-33 (Kp = 14.3 mag), there are periodic dimmings of 0.23% lasting 4.2 hours and occurring every 5.4 d (Fig. 1). The ensemble of transits are detected at a combined signal-to-noise ratio of ≈ 32. During the K2 observations, cool, dark regions on the stellar surface (starspots) rotated in and out of view, producing semi-sinusoidal brightness variations of ∼3% peak-to-trough amplitude with a 6.3 ± 0.2 d periodicity (Extended Data Fig. 1). We removed the starspot variability prior to modeling the transit events. We fit the transit profiles using established methods 10, measuring the planet's size relative to its host star and its orbital geometry (Table 1).K2-33 is an established member of the Upper Scorpius OB association 11,12 , the nearest site , which we confirm from Keck spectra (Table 1). Furthermore, the stellar rotation rate we measure via broadening of absorption lines in the spectra and via the starspot period (Table 1), is rapid relative to field-age stars of similar mass 14 . We determined the star's systemic RV (Table 1) The inferred planet size and mass depend directly upon the host sta...

Artículo de publicación ISIIn the 1980s, excess infrared emission was discovered around main-sequence stars; subsequent direct-imaging observations revealed orbiting disks of cold dust to be the source(1). These 'debris disks' were thought to be by-products of planet formation because they often exhibited morphological and brightness asymmetries that may result from gravitational perturbation by planets. This was proved to be true for the beta Pictoris system, in which the known planet generates an observable warp in the disk(2-5). The nearby, young, unusually active late-type star AU Microscopii hosts a well-studied edge-on debris disk; earlier observations in the visible and near-infrared found asymmetric localized structures in the form of intensity variations along the midplane of the disk beyond a distance of 20 astronomical units(6-9). Here we report high-contrast imaging that reveals a series of five large-scale features in the southeast side of the disk, at projected separations of 10-60 astronomical units, persisting over intervals of 1-4 years. All these features appear to move away from the star at projected speeds of 4-10 kilometres per second, suggesting highly eccentric or unbound trajectories if they are associated with physical entities. The origin, localization, morphology and rapid evolution of these features are difficult to reconcile with current theories.ESO Very Large Telescope 60.A-9249 NASA/ESA Hubble Space Telescope 12228 NASA NAS 5-26555 ANR-14-CE33-001