Exoplanet detections have revolutionized astronomy, offering new insights into solar system architecture and planet demographics. While nearly 1,900 exoplanets have now been discovered and confirmed(1), none are still in the process of formation. Transition disks, protoplanetary disks with inner clearings(2-4) best explained by the influence of accreting planets(5), are natural laboratories for the study of planet formation. Some transition disks show evidence for the presence of young planets in the form of disk asymmetries(6,7) or infrared sources detected within their clearings, as in the case of LkCa 15 (refs 8, 9). Attempts to observe directly signatures of accretion onto protoplanets have hitherto proven unsuccessful(10). Here we report adaptive optics observations of LkCa 15 that probe within the disk clearing. With accurate source positions over multiple epochs spanning 2009-2015, we infer the presence of multiple companions on Keplerian orbits. We directly detect Ha emission from the innermost companion, LkCa 15 b, evincing hot (about 10,000 kelvin) gas falling deep into the potential well of an accreting protoplanet.

The only known compound of sodium and hydrogen is archetypal ionic NaH. Application of high pressure is known to promote states with higher atomic coordination, but extensive searches for polyhydrides with unusual stoichiometry have had only limited success in spite of several theoretical predictions. Here we report the first observation of the formation of polyhydrides of Na (NaH3 and NaH7) above 40GPa and 2,000 K. We combine synchrotron X-ray diffraction and Raman spectroscopy in a laser-heated diamond anvil cell and theoretical random structure searching, which both agree on the stable structures and compositions. Our results support the formation of multicenter bonding in a material with unusual stoichiometry. These results are applicable to the design of new energetic solids and high-temperature superconductors based on hydrogen-rich materials.

We report the discovery of a scattering component around the HD 141569 A circumstellar debris system, interior to the previously known inner ring. The discovered inner disk component, obtained in broadband optical light with Hubble Space Telescope/Space Telescope Imaging Spectrograph coronagraphy, was imaged with an inner working angle of 0 25, and can be traced from 0 ''.4 (similar to 46 AU) to 1 ''.0 (similar to 116 AU) after deprojection using i = 55 degrees. The inner disk component is seen to forward scatter in a manner similar to the previously known rings, has a pericenter offset of similar to 6 AU, and break points where the slope of the surface brightness changes. It also has a spiral arm trailing in the same sense as other spiral arms and arcs seen at larger stellocentric distances. The inner disk spatially overlaps with the previously reported warm gas disk seen in thermal emission. We detect no point sources within 2 ''(similar to 232 AU), in particular in the gap between the inner disk component and the inner ring. Our upper limit of 9 +/- 3 M-J is augmented by a new dynamical limit on single planetary mass bodies in the gap between the inner disk component and the inner ring of 1 M-J, which is broadly consistent with previous estimates.

The search of compounds with CxNy composition holds great promise for creating materials which would rival diamond in hardness due to the very strong covalent C-N bond. Early theoretical and experimental works on CxNy compounds were based on the hypothetical structural similarity of predicted C3N4 phases with known binary A(3)B(4) structural types; however, the synthesis of C3N4 other than g-C3N4 remains elusive. Here, we explore an elemental synthesis at high pressures and temperatures in which the compositional limitations due to the use of precursors in the early works are substantially lifted. Using in situ synchrotron X-ray diffraction and Raman spectroscopy, we demonstrate the synthesis of a highly incompressible Pnnm CN compound (x = y = 1) with sp(3)-hybridized carbon above 55 GPa and 7000 K. This result is supported by first-principles evolutionary search, which finds that CN is the most stable compound above 14 GPa. On pressure release below 6 GPa, the synthesized CN compound amorphizes, maintaining its 1:1 stoichiometry as confirmed by energy-dispersive X-ray spectroscopy. This work underscores the importance of understanding the novel high-pressure chemistry laws that promote extended 3D C-N structures, never observed at ambient conditions. Moreover, it opens a new route for synthesis of superhard materials based on novel stoichiometries

Transition disks (TDs) are intermediate stage circumstellar disks characterized by an inner gap within the disk structure. To test whether these gaps may have been formed by closely orbiting, previously undetected stellar companions, we collected high-resolution optical spectra of 31 TD objects to search for spectroscopic binaries (SBs). Twenty-four of these objects are in Ophiuchus and seven are within the Coronet, Corona Australis, and Chameleon I star-forming regions. We measured radial velocities for multiple epochs, obtaining a median precision of 400 ms(-1). We identified double-lined SB SSTc2d J163154.7-250324 in Ophiuchus, which we determined to be composed of a K7(+/- 0.5) and a K9(+/- 0.5) star, with orbital limits of a < 0.6 au and P < 150 days. This results in an SB fraction of 0.04(-0.03+)(0.12) in Ophiuchus, which is consistent with other spectroscopic surveys of non-TD objects in the region. This similarity suggests that TDs are not preferentially sculpted by the presence of close binaries and that planet formation around close binaries may take place over similar timescales to that around single stars.

Synthesis of high nitrogen containing materials has been the subject of research interest for use as alternative clean sources of fuel and explosives. Here we present experimental evidence for the photochemical synthesis of new energetic materials from sodium azide (NaN3) at 4.88.1 GPa. We show that excitation into the conduction band generates color centers within the compressed alpha-NaN3 phase lattice with minimal or no molecular N-2 evolution. Photochemical changes to the sample were monitored by X-ray diffraction (XRD), infrared (IR) absorption, and Raman spectroscopy. These high pressure products were found to be stable upon decompression at 300 K down to 1.6 GPa, although it is suspected that the material can be recoverable to ambient pressure with cold decompression.

The ability of Earth's mantle to conduct heat by radiation is determined by optical properties of mantle phases. Optical properties of mantle minerals at high pressure are accessible through diamond anvil cell experiments, but because of the intense thermal radiation at T > 1000 K such studies are limited to lower temperatures. Accordingly, radiative thermal conductivity at mantle conditions has been evaluated with the assumption of the temperature-independent optical properties. Particularly uncertain is the temperature-dependence of optical properties of lower mantle minerals across the spin transition, as the spin state itself is a strong function of temperature. Here we use laser-heated diamond anvil cells combined with a pulsed ultra-bright supercontinuum laser probe and a synchronized time-gated detector to examine optical properties of high and low spin ferrous iron at 45-73 GPa up to 1600 K in an octahedral crystallographic unit (FeO6), one of the most abundant building blocks in the mantle. Siderite (FeCO3) is used as a model for FeO6-octahedra as it contains no ferric iron and exhibits a sharp optically apparent pressure-induced spin transition at 44 GPa, simplifying data interpretation. We find that the optical absorbance of low spin FeO6 increases with temperature due to the partially lifted Laporte selection rule. The temperature-induced low-to-high spin transition, however, results in a dramatic drop in absorbance of the FeO6 unit in siderite. The absorption edge (Fe-O charge transfer) red-shifts (similar to 1 cm(-1)/K) with increasing temperature and at T > 1600 K and P > 70 GPa becomes the dominant absorption mechanism in the visible range, suggesting its superior role in reducing the ability of mantle minerals to conduct heat by radiation. This implies that the radiative thermal conductivity of analogous FeO6-bearing minerals such as ferropericlase, the second most abundant mineral in the Earth's lower mantle, is substantially reduced approaching the core-mantle boundary conditions. (C) 2016 Elsevier B.V. All rights reserved.

The Large Binocular Telescope Interferometer (LBTI) is a versatile instrument designed for high angular resolution and high-contrast infrared imaging (1.5-13 mu m). In this paper, we focus on the mid-infrared (8-13 mu m) nulling mode and present its theory of operation, data reduction, and on-sky performance as of the end of the commissioning phase in 2015 March. With an interferometric baseline of 14.4 m, the LBTI nuller is specifically tuned to resolve the habitable zone of nearby main-sequence stars, where warm exozodiacal dust emission peaks. Measuring the exozodi luminosity function of nearby main-sequence stars is a key milestone to prepare for future exo-Earth direct imaging instruments. Thanks to recent progress in wavefront control and phase stabilization, as well as in data reduction techniques, the LBTI demonstrated in 2015 February a calibrated null accuracy of 0.05% over a 3 hr long observing sequence on the bright nearby A3V star beta Leo. This is equivalent to an exozodiacal disk density of 15-30. zodi for a Sun-like star located at 10 pc, depending on the adopted disk model. This result sets a new record for high-contrast mid-infrared interferometric imaging and opens a new window on the study of planetary systems.

Synchrotron x-ray diffraction and Raman spectroscopy have been used to study the chemical reactions of molecular hydrogen (H-2) with sulfur (S) at high pressures. We find theoretically predicted Cccm and Im (3) over barm H3S to be the reaction products at 50 and 140 GPa, respectively. Im (3) over barm H3S is a stable crystalline phase above 140 GPa and it transforms to R3mH(3)S on pressure release below 140 GPa. The latter phase is (meta) stable down to at least 70 GPa where it transforms to Cccm H3S upon annealing (T < 1300 K) to overcome the kinetic hindrance. Cccm H3S has an extended structure with symmetric hydrogen bonds at 50 GPa, and upon decompression it experiences a transformation to a molecular mixed H2S-H-2 structure below 40 GPa without any apparent change in the crystal symmetry.

The elasticity at high pressure of solid hydrogen in hexagonal close-packed (hcp) phase I has been examined experimentally by laser acoustics technique in a diamond anvil cell, up to 55 GPa at 296 K, and theoretically using pair and three-body semiempirical potentials, up to 160 GPa. In the experiments on H-2 and D-2, the compressional sound velocity has been measured; the Poisson's ratio has been determined by combining these data with the previously reported equation of state. At room temperature, the difference between the adiabatic and isothermal processes vanishes above 25 GPa but cannot be neglected at lower pressure. Theoretically, all five elastic constants of hcp hydrogen have been calculated, and various derived elastic quantities are presented. The elastic anisotropy of hcp hydrogen was found to be significant, with Delta P approximate to 1.2, Delta S-1 Delta approximate to 1.7, and Delta S-2 approximate to 1. Calculations suggest the Poisson's ratio to decrease with pressure reaching a minimum value of 0.28 at 145 GPa. In the experiment, the Poisson's ratio is also found to decrease with pressure. Theoretical calculations show that the inclusion of zero-point vibrations on the elastic properties of H-2 does not result in any drastic changes of the behavior of the elastic quantities.