Magnetic fields are important contributors to the dynamics of collapsing molecular cloud cores, and can have a major effect on whether collapse results in a single protostar or fragmentation into a binary or multiple protostar system. New models are presented of the collapse of magnetic cloud cores using the adaptive mesh refinement code Enzo2.0. The code was used to calculate the ideal magnetohydrodynamics (MHD) of initially spherical, uniform density, and rotation clouds with density perturbations, i.e., the Boss & Bodenheimer standard isothermal test case for three-dimensional (3D) hydrodynamics codes. After first verifying that Enzo reproduces the binary fragmentation expected for the non-magnetic test case, a large set of models was computed with varied initial magnetic field strengths and directions with respect to the cloud core axis of rotation (parallel or perpendicular), density perturbation amplitudes, and equations of state. Three significantly different outcomes resulted: (1) contraction without sustained collapse, forming a denser cloud core; (2) collapse to form a single protostar with significant spiral arms; and (3) collapse and fragmentation into binary or multiple protostar systems, with multiple spiral arms. Comparisons are also made with previous MHD calculations of similar clouds with a barotropic equations of state. These results for the collapse of initially uniform density spheres illustrate the central importance of both magnetic field direction and field strength for determining the outcome of dynamic protostellar collapse.

We present the results of a search for planetary companions orbiting near hot Jupiter planet candidates (Jupiter-size candidates with orbital periods near 3 d) identified in the Kepler data through its sixth quarter of science operations. Special emphasis is given to companions between the 2: 1 interior and exterior mean-motion resonances. A photometric transit search excludes companions with sizes ranging from roughly two-thirds to five times the size of the Earth, depending upon the noise properties of the target star. A search for dynamically induced deviations from a constant period (transit timing variations) also shows no significant signals. In contrast, comparison studies of warm Jupiters (with slightly larger orbits) and hot Neptune-size candidates do exhibit signatures of additional companions with these same tests. These differences between hot Jupiters and other planetary systems denote a distinctly different formation or dynamical history.

Isotopic abundances of short-lived radioisotopes such as Al-26 appear to provide precise chronometers of events in the early Solar System, assuming that they were initially homogeneously distributed. However, both Fe-60 and Al-26 were likely formed in a supernova and then injected into the solar nebula in a highly heterogeneous manner. Conversely, the abundances in primitive meteorites of the three stable oxygen isotopes exhibitmass-independent fractionations that somehow survived homogenization in the solar nebula. Both the presence of refractory particles in Comet 81P/Wild 2 and the anomalously high crystallinity observed in protoplanetary disks may require large-scale outward radial transport from the hotter inner disk regions, even as disk gas accretes onto the central protostar. We examine here theoretical efforts to solve these seemingly disparate cosmochemical puzzles and conclude that the mixing and transport produced by a phase of marginal gravitational instability appears to meet all of these constraints.

Giant planet formation by gravitational disc instabilities has become theoretically and observationally acceptable at large distances, but remains theoretically contentious at distances inside about 20 au. Several new three-dimensional hydrodynamics models are presented, where radiative transfer is handled in the flux-limited diffusion approximation from the very start of the model, rather than being employed only after clumps have begun to form. The three models show that the use of the flux limiter has little appreciable effect on the early evolution of a disc instability, in agreement with the conclusions of the previous models, which studied later phases. In addition, two new models are presented where the central protostar is either held fixed or is allowed to wobble in such a manner as to preserve the centre of mass of the stardisc system. While spiral arms and clumps form in both models, the wobbling protostar model appears to be better able to form self-gravitating clumps that could contract to form gas giant protoplanets. Combined with previous results, the new models imply that disc instability should be able to form self-gravitating clumps inside, as well as outside, 20 au in suitably massive and cool protoplanetary discs.

The solar nebula is thought to have undergone a number of episodes of FU Orionis outbursts during its early evolution. We present here the first calculations of the trajectories of particles in a marginally gravitationally unstable solar nebula during an RI Orionis outburst, which show that 0.1-10 cm-sized particles traverse radial distances of 10 AU or more, inward and outward, in less than 200 yrs, exposing the particles to temperatures from similar to 60 K to similar to 1500 K. Such trajectories can thus account for the discovery of refractory particles in comets. Refractory particles should acquire Wark-Lovering-like rims as they leave the highest temperature regions of the disk, and these rims should have significant variations in their stable oxygen isotope ratios. Particles are likely to be heavily modified or destroyed if they pass within 1 AU of the Sun, and so are only likely to survive if they formed in the final few FU Orionis outbursts, or were transported to the outer reaches of the solar system. Calcium, aluminum-rich inclusions (CAIs) from primitive meteorites are the oldest known solar system objects and have a very narrow age range. Most CAIs may have formed at the end of the FU Orionis outbursts phase, with an age range reflecting the period between the last few outbursts. (C) 2012 Elsevier B.V. All rights reserved.

A variety of stellar sources have been proposed for the origin of the short-lived radioisotopes that existed at the time of the formation of the earliest solar system solids, including Type II supernovae (SNe), asymptotic giant branch (AGB) and super-AGB stars, and Wolf-Rayet star winds. Our previous adaptive mesh hydrodynamics models with the FLASH2.5 code have shown which combinations of shock wave parameters are able to simultaneously trigger the gravitational collapse of a target dense cloud core and inject significant amounts of shock wave gas and dust, showing that thin SN shocks may be uniquely suited for the task. However, recent meteoritical studies have weakened the case for a direct SN injection to the presolar cloud, motivating us to re-examine a wider range of shock wave and cloud core parameters, including rotation, in order to better estimate the injection efficiencies for a variety of stellar sources. We find that SN shocks remain as the most promising stellar source, though planetary nebulae resulting from AGB star evolution cannot be conclusively ruled out. Wolf-Rayet (WR) star winds, however, are likely to lead to cloud core shredding, rather than to collapse. Injection efficiencies can be increased when the cloud is rotating about an axis aligned with the direction of the shock wave, by as much as a factor of similar to 10. The amount of gas and dust accreted from the post-shock wind can exceed that injected from the shock wave, with implications for the isotopic abundances expected for a SN source.

The Thermal Infrared imager for the GMT which provides Extreme contrast and Resolution (TIGER) is intended as a small-scale, targeted instrument capable of detecting and characterizing exoplanets and circumstellar disks, around both young systems in formation, and more mature systems in the solar neighborhood. TIGER can also provide general purpose infrared imaging at wavelengths from 1.5-14 mu m. The instrument will utilize the facility adaptive optics (AO) system. With its operation at NIR to MIR wavelengths (where good image quality is easier to achieve), and much of the high-impact science using modestly bright guide stars, the instrument can be used early in the operation of the GMT.

Analyses of primitive meteorites and cometary samples have shown that the solar nebula must have experienced a phase of large-scale outward transport of small refractory grains as well as homogenization of initially spatially heterogeneous short-lived isotopes. The stable oxygen isotopes, however, were able to remain spatially heterogeneous at the similar to 6% level. One promising mechanism for achieving these disparate goals is the mixing and transport associated with a marginally gravitationally unstable (MGU) disk, a likely cause of FU Orionis events in young low-mass stars. Several new sets of MGU models are presented that explore mixing and transport in disks with varied masses (0.016 to 0.13 M-circle dot) around stars with varied masses (0.1 to 1 M-circle dot) and varied initial Q stability minima (1.8 to 3.1). The results show that MGU disks are able to rapidly (within similar to 10(4) yr) achieve large-scale transport and homogenization of initially spatially heterogeneous distributions of disk grains or gas. In addition, the models show that while single-shot injection heterogeneity is reduced to a relatively low level (similar to 1%), as required for early solar system chronometry, continuous injection of the sort associated with the generation of stable oxygen isotope fractionations by UV photolysis leads to a sustained, relatively high level (similar to 10%) of heterogeneity, in agreement with the oxygen isotope data. These models support the suggestion that the protosun may have experienced at least one FU Orionis-like outburst, which produced several of the signatures left behind in primitive chondrites and comets.

We have completed a high-contrast direct imaging survey for giant planets around 57 debris disk stars as part of the Gemini NICI Planet-Finding Campaign. We achieved median H-band contrasts of 12.4 mag at 0.'' 5 and 14.1 mag at 1 '' separation. Follow-up observations of the 66 candidates with projected separation <500 AU show that all of them are background objects. To establish statistical constraints on the underlying giant planet population based on our imaging data, we have developed a new Bayesian formalism that incorporates (1) non-detections, (2) single-epoch candidates, (3) astrometric and (4) photometric information, and (5) the possibility of multiple planets per star to constrain the planet population. Our formalism allows us to include in our analysis the previously known beta Pictoris and the HR 8799 planets. Our results show at 95% confidence that <13% of debris disk stars have a >= 5 M-Jup planet beyond 80 AU, and <21% of debris disk stars have a >= 3 M-Jup planet outside of 40 AU, based on hot-start evolutionary models. We model the population of directly imaged planets as d(2)N/dMda proportional to m(alpha)a(beta), where m is planet mass and a is orbital semi-major axis (with a maximum value of a(max)). We find that beta < -0.8 and/or alpha > 1.7. Likewise, we find that beta < -0.8 and/or a(max) < 200 AU. For the case where the planet frequency rises sharply with mass (alpha > 1.7), this occurs because all the planets detected to date have masses above 5 M-Jup, but planets of lower mass could easily have been detected by our search. If we ignore the beta Pic and HR 8799 planets (should they belong to a rare and distinct group), we find that <20% of debris disk stars have a >= 3 M-Jup planet beyond 10 AU, and beta < -0.8 and/or alpha < -1.5. Likewise, beta < -0.8 and/or a(max) < 125 AU. Our Bayesian constraints are not strong enough to reveal any dependence of the planet frequency on stellar host mass. Studies of transition disks have suggested that about 20% of stars are undergoing planet formation; our non-detections at large separations show that planets with orbital separation >40 AU and planet masses >3 M-Jup do not carve the central holes in these disks.