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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% ).

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 two epochs of MPG/ESO 2.2m GROND simultaneous 6-band (r ′ i ′ z ′ JHK) photometric monitoring of the closest known L/T transition brown dwarf binary WISE J104915.57-531906.1AB. We report here the first resolved variability monitoring of both the T0.5 and L7.5 components. We obtained 4 hours of focused observations on the night of UT 2013-04-22, as well as 4 hours of defocused (unresolved) observations on the night of UT 2013-04-16. We note a number of robust trends in our light curves. The r ′ and i ′ light curves appear to be anticorrelated with z ′ and H for the T0.5 component and in the unresolved lightcurve. In the defocused dataset, J appears correlated with z ′ and H and anticorrelated with r ′ and i ′ , while in the focused dataset we measure no variability for J at the level of our photometric precision, likely due to evolving weather phenomena. In our focused T0.5 component lightcurve, the K band lightcurve displays a significant phase offset relative to both H and z ′ . We argue that the measured phase offsets are correlated with atmospheric pressure probed at each band, as estimated from 1D atmospheric models. We also report low-amplitude variability in i ′ and z ′ intrinsic to the L7.5 component.

As part of our ongoing NTT SoFI survey for variability in young free-floating planets and low mass brown dwarfs, we detect significant variability in the young, free-floating planetary mass object PSO J318.5-22, likely due to rotational modulation of inhomogeneous cloud cover. A member of the 23±3 Myr β Pic moving group, PSO J318.5-22 has T eff = 1160 +30 −40 K and a mass estimate of 8.3±0.5 M Jup for a 23±3 Myr age. PSO J318.5-22 is intermediate in mass between 51 Eri b and β Pic b, the two known exoplanet companions in the β Pic moving group. With variability amplitudes from 7-10% in J S at two separate epochs over 3-5 hour observations, we constrain the rotational period of this object to >5 hours. In K S , we marginally detect a variability trend of up to 3% over a 3 hour observation. This is the first detection of weather on an extrasolar planetary mass object. Among L dwarfs surveyed at high-photometric precision (<3%) this is the highest amplitude variability detection. Given the low surface gravity of this object, the high amplitude preliminarily suggests that such objects may be more variable than their high mass counterparts, although observations of a larger sample is necessary to confirm this. Measuring similar variability for directly imaged planetary companions is possible with instruments such as SPHERE and GPI and will provide important constraints on formation.Measuring variability at multiple wavelengths can help constrain cloud structure.1 Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 095.C-0590

We present the results of a deep wide‐field near‐infrared survey of 12 deg2 of the Pleiades conducted as part of the United Kingdom Infrared Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS) Galactic Cluster Survey (GCS). We have extracted over 340 high‐probability proper motion (PM) members down to 0.03 M⊙ using a combination of UKIDSS photometry and PM measurements obtained by cross‐correlating the GCS with data from the Two Micron All Sky Survey, the Isaac Newton Telescope and the Canada–France–Hawaii Telescope. Additionally, we have unearthed 73 new candidate brown dwarf (BD) members on the basis of five‐band UKIDSS photometry alone. We have identified 23 substellar multiple system candidates out of 63 candidate BDs from the (Y−K, Y) and (J−K, J) colour–magnitude diagrams, yielding a binary frequency of 28–44 per cent in the 0.075−0.030 M⊙ mass range. Our estimate is three times larger than the binary fractions reported from high‐resolution imaging surveys of field ultracool dwarfs and Pleiades BDs. However, it is marginally consistent with our earlier ‘peculiar’ photometric binary fraction of 50 ± 10 per cent presented by Pinfield et al., in good agreement with the 32–45 per cent binary fraction derived from the recent Monte Carlo simulations of Maxted & Jeffries and compatible with the 26 ± 10 per cent frequency recently estimated by Basri & Reiners. A tentative estimate of the mass ratios from photometry alone seems to support the hypothesis that binary BDs tend to reside in near equal‐mass ratio systems. In addition, the recovery of four Pleiades members targeted by high‐resolution imaging surveys for multiplicity studies suggests that half of the binary candidates may have separations below the resolution limit of the Hubble Space Telescope or current adaptive optics facilities at the distance of the Pleiades (a ∼7 au). Finally, we have derived luminosity and mass functions from the sample of photometric candidates with membership probabilities. The mass function is well modelled by a lognormal peaking at 0.24 M⊙ and is in agreement with previous studies in the Pleiades.

Abstract. In this paper we present surveys of two open clusters using photometry and accurate astrometry from the SuperCOSMOS microdensitometer. These use plates taken by the Palomar Oschin Schmidt Telescope giving a wide field (5• from the cluster centre in both cases), accurate positions and a long time baseline for the proper motions. Distribution functions are fitted to proper motion vector point diagrams yielding formal membership probabilities. Luminosity and mass functions are then produced along with a catalogue of high probability members. Background star contamination limited the depth of the study of Alpha Per to R = 18. Due to this the mass function found for this cluster could only be fitted with a power law (ξ(m) = m −α ) with α = 0.86 +0.14 −0.19 . However with the better seperation of the Pleiades' cluster proper motion from the field population results were obtained down to R = 21. As the mass function produced for this cluster extends to lower masses it is possible to see the gradient becoming increasingly shallow. This mass function is well fitted by a log normal distribution.

We present the results of a deep wide‐field near‐infrared survey of the entire Pleiades cluster recently released as part of the UKIRT Infrared Deep Sky Survey (UKIDSS) Galactic Clusters Survey (GCS) Data Release 9 (DR9). We have identified a sample of ∼1000 Pleiades cluster member candidates combining photometry in five near‐infrared passbands and proper motions derived from the multiple epochs provided by the UKIDSS GCS DR9. We also provide revised membership for all previously published Pleiades low‐mass stars and brown dwarfs in the past decade recovered in the UKIDSS GCS DR9 Pleiades survey based on the new photometry and astrometry provided by the GCS. We find no evidence of K‐band variability in the Pleiades members larger than ∼0.08 mag. In addition, we infer a substellar binary frequency of 22–31 per cent in the 0.075–0.03 M⊙ range for separations less than ∼100 au. We employed two independent but complementary methods to derive the cluster luminosity and mass functions: a probabilistic analysis and a more standard approach consisting of stricter astrometric and photometric cuts. We found that the resulting luminosity and mass functions obtained from both methods are very similar. We derive the Pleiades mass function in the 0.6–0.03 M⊙ range and found that it is best reproduced by a lognormal representation with a mean characteristic mass of 0.20 ± 0.05 M⊙, in agreement with earlier studies and the extrapolation of the field mass function.