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A new speckle and wide-field imaging instrument for the WIYN telescope called NN-EXPLORE Exoplanet Stellar Speckle Imager (NESSI) is described. NESSI offers simultaneous two-color diffraction-limited imaging and wide-field traditional imaging for validation and characterization of transit and precision RV exoplanet studies. Many exoplanet targets will come from the NASA K2 and Transiting Exoplanet Survey Satellite (TESS) missions. NESSI is capable of resolving close binaries at sub-arcsecond separations down to the diffraction limit and >6 mag contrast difference in the visible band on targets as faint as 14th mag. Preliminary results from the instrument commissioning at WIYN and demonstrations of the instrument's capabilities are presented.

The quest for Earth-like planets is a major focus of current exoplanet research. Although planets that are Earth-sized and smaller have been detected, these planets reside in orbits that are too close to their host star to allow liquid water on their surfaces. We present the detection of Kepler-186f, a 1.11 ± 0.14 Earth-radius planet that is the outermost of five planets, all roughly Earth-sized, that transit a 0.47 ± 0.05 solar-radius star. The intensity and spectrum of the star's radiation place Kepler-186f in the stellar habitable zone, implying that if Kepler-186f has an Earth-like atmosphere and water at its surface, then some of this water is likely to be in liquid form.

The transits of two Sun-like stars by small planets in an open star cluster are reported; such a stellar environment is unlike that of most planet-hosting field stars, and suggests that the occurrence of planets is unaffected by the stellar environment in open clusters. A global rate of planet formation Until now only four planets — with masses similar to Jupiter — have been found orbiting stars in old open clusters, compared with more than 800 — mostly Neptune-sized — orbiting 'field stars' outside clusters. Most stars and planets form in open clusters that break up within a few hundred million years as stars drift away to become field stars. Older open clusters survive because they were denser in stars when they formed, a stellar environment very different from that of other planet-hosting field stars. This paper, part of the Kepler Cluster Study, describes observations of the transits of two Sun-like stars by planets smaller than Neptune in the 1-billion-year-old open cluster NGC6811. This demonstrates that small planets can form and survive in a dense cluster environment, and implies that the frequency and properties of planets in open clusters are consistent with those of planets around field stars in our Galaxy. Most stars and their planets form in open clusters. Over 95 per cent of such clusters have stellar densities too low (less than a hundred stars per cubic parsec) to withstand internal and external dynamical stresses and fall apart within a few hundred million years 1 . Older open clusters have survived by virtue of being richer and denser in stars (1,000 to 10,000 per cubic parsec) when they formed. Such clusters represent a stellar environment very different from the birthplace of the Sun and other planet-hosting field stars. So far more than 800 planets have been found around Sun-like stars in the field 2 . The field planets are usually the size of Neptune or smaller 3 , 4 , 5 . In contrast, only four planets have been found orbiting stars in open clusters 6 , 7 , 8 , all with masses similar to or greater than that of Jupiter. Here we report observations of the transits of two Sun-like stars by planets smaller than Neptune in the billion-year-old open cluster NGC6811. This demonstrates that small planets can form and survive in a dense cluster environment, and implies that the frequency and properties of planets in open clusters are consistent with those of planets around field stars in the Galaxy.

The K2 mission will make use of the Kepler spacecraft and its assets to expand upon Kepler's groundbreaking discoveries in the fields of exoplanets and astrophysics through new and exciting observations. K2 will use an innovative way of operating the spacecraft to observe target fields along the ecliptic for the next 2-3 years. Early science commissioning observations have shown an estimated photometric precision near 400 ppm in a single 30 minute observation, and a 6-hr photometric precision of 80 ppm (both at V = 12). The K2 mission offers long-term, simultaneous optical observation of thousands of objects at a precision far better than is achievable from ground-based telescopes. Ecliptic fields will be observed for approximately 75 days enabling a unique exoplanet survey which fills the gaps in duration and sensitivity between the Kepler and TESS missions, and offers pre-launch exoplanet target identification for JWST transit spectroscopy. Astrophysics observations with K2 will include studies of young open clusters, bright stars, galaxies, supernovae, and asteroseismology.

NASA's exoplanet Discovery mission Kepler was reconstituted as the K2 mission a year after the failure of the second of Kepler's four reaction wheels in 2013 May. Fine control of the spacecraft pointing is now accomplished through the use of the two remaining well-functioning reaction wheels and balancing the pressure of sunlight on the solar panels, which constrains K2 observations to fields in the ecliptic for up to approximately 80 days each. This pseudo-stable mechanism gives typical roll motion in the focal plane of 1.0 pixels peak-to-peak over 6 hr at the edges of the field, two orders of magnitude greater than typical 6 hr pointing errors in the Kepler primary mission. Despite these roll errors, the joint performance of the flight system and its modified science data processing pipeline restores much of the photometric precision of the primary mission while viewing a wide variety of targets, thus turning adversity into diversity. We define K2 performance metrics for data compression and pixel budget available in each campaign; the photometric noise on exoplanet transit and stellar activity timescales; residual correlations in corrected long-cadence light curves; and the protection of test sinusoidal signals from overfitting in the systematic error removal process. We find that data compression and noise both increase linearly with radial distance from the center of the field of view, with the data compression proportional to star count as well. At the center, where roll motion is nearly negligible, the limiting 6 hr photometric precision for a quiet 12th magnitude star can be as low as 30 ppm, only 25% higher than that of Kepler. This noise performance is achieved without sacrificing signal fidelity; test sinusoids injected into the data are attenuated by less than 10% for signals with periods upto 15 days, so that a wide range of stellar rotation and variability signatures are preserved by the K2 pipeline. At timescales relevant to asteroseismology, light curves derived from K2 archive calibrated pixels have high-frequency noise amplitude within 40% of that achieved by Kepler. The improvements in K2 operations and science data analysis resulting from 1.5 years of experience with this new mission concept, and quantified by the metrics in this paper, will support continuation of K2's already high level of scientific productivity in an extended K2 mission.

ABSTRACT We present the motivations for and methods we used to create a new ground-based photometric survey of the field targeted by the NASA Kepler Mission. The survey contains magnitudes for 4,416,007 sources in one or more of the UBV filters, including 1,861,126 sources detected in all three filters. The typical completeness limit is U ∼ 18.7, B ∼ 19.3, and V ∼ 19.1 mag, but varies by location. The area covered is 191 deg2 and includes the areas on and between the 42 Kepler CCDs, as well as additional areas around the perimeter of the Kepler field. The major significance of this survey is our addition of U to the optical bandpass coverage available in the Kepler Input Catalog, which was primarily limited to the redder SDSS griz and D51 filters. The U coverage reveals a sample of the hottest sources in the field, many of which are not currently targeted by Kepler, but may be objects of astrophysical interest.

ABSTRACT Fringing in CCD images is troublesome from the aspect of photometric quality and image flatness in the final reduced product. Additionally, defringing during calibration requires the inefficient use of time during the night to collect and produce a \"supersky\" fringe frame. The fringe pattern observed in a CCD image for a given near-IR filter is dominated by small thickness variations across the detector, with a second-order effect caused by the wavelength extent of the emission lines within the bandpass that produce the interference pattern. We show that essentially any set of emission lines that generally match the wavelength coverage of the night-sky emission lines within a bandpass will produce an identical fringe pattern. We present an easy, inexpensive, and efficient method that uses a neon lamp as a flat-field source and produces high-S/N fringe frames to use for defringing an image during the calibration process.

Two exoplanets of Earth’s size have been discovered in orbit around the star Kepler-20. Since the discovery of the first extrasolar giant planets around Sun-like stars 1 , 2 , evolving observational capabilities have brought us closer to the detection of true Earth analogues. The size of an exoplanet can be determined when it periodically passes in front of (transits) its parent star, causing a decrease in starlight proportional to its radius. The smallest exoplanet hitherto discovered 3 has a radius 1.42 times that of the Earth’s radius ( R ⊕ ), and hence has 2.9 times its volume. Here we report the discovery of two planets, one Earth-sized (1.03 R ⊕ ) and the other smaller than the Earth (0.87 R ⊕ ), orbiting the star Kepler-20, which is already known to host three other, larger, transiting planets 4 . The gravitational pull of the new planets on the parent star is too small to measure with current instrumentation. We apply a statistical method to show that the likelihood of the planetary interpretation of the transit signals is more than three orders of magnitude larger than that of the alternative hypothesis that the signals result from an eclipsing binary star. Theoretical considerations imply that these planets are rocky, with a composition of iron and silicate. The outer planet could have developed a thick water vapour atmosphere.

The K2 mission has enabled searches for transits in crowded stellar environments very different from the original Kepler mission field. We describe here the reduction and analysis of time series data from K2's Campaign 0 superstamp, which contains the 150 Myr open cluster M35. We report on the identification of a substellar transiting object orbiting an A star at the periphery of the superstamp. To investigate this transiting source, we performed ground based follow-up observations, including photometry with the Las Cumbres Observatory telescope network and high resolution spectroscopy with Keck/High Resolution Echelle Spectrometer. We confirm that the host star is a hot, rapidly rotating star, precluding precision radial velocity measurements. We nevertheless present a statistical validation of the planet or brown dwarf candidate using speckle interferometry from the WIYN telescope to rule out false positive stellar eclipsing binary scenarios. Based on parallax and proper motion data from Gaia Data Release 2 (DR2), we conclude that the star is not likely to be a member of M35, but instead is a background star around 100 pc behind the cluster. We present an updated ephemeris to enable future transit observations. We note that this is a rare system as a hot host star with a substellar companion. It has a high potential for future follow-up, including Doppler tomography and mid-infrared secondary transit observations.