The disk instability mechanism for giant planet formation is based on the formation of clumps in a marginally gravitationally unstable protoplanetary disk, which must lose thermal energy through a combination of convection and radiative cooling if they are to survive and contract to become giant protoplanets. While there is good observational support for forming at least some giant planets by disk instability, the mechanism has become theoretically contentious, with different three-dimensional radiative hydrodynamics codes often yielding different results. Rigorous code testing is required to make further progress. Here we present two new analytical solutions for radiative transfer in spherical coordinates, suitable for testing the code employed in all of the Boss disk instability calculations. The testing shows that the Boss code radiative transfer routines do an excellent job of relaxing to and maintaining the analytical results for the radial temperature and radiative flux profiles for a spherical cloud with high or moderate optical depths, including the transition from optically thick to optically thin regions. These radial test results are independent of whether the Eddington approximation, diffusion approximation, or flux-limited diffusion approximation routines are employed. The Boss code does an equally excellent job of relaxing to and maintaining the analytical results for the vertical (theta) temperature and radiative flux profiles for a disk with a height proportional to the radial distance. These tests strongly support the disk instability mechanism for forming giant planets.

We present an analysis of three years of precision radial velocity (RV) measurements of 160 metal-poor stars observed with HIRES on the Keck 1 telescope. We report on variability and long-term velocity trends for each star in our sample. We identify several long-term, low-amplitude RV variables worthy of followup with direct imaging techniques. We place lower limits on the detectable companion mass as a function of orbital period. Our survey would have detected, with a 99.5% confidence level, over 95% of all companions on low-eccentricity orbits with velocity semiamplitude K greater than or similar to 100 m s(-1), or M-p sin i greater than or similar to 3.0 M-J(P/yr)((1/3)), for orbital periods P less than or similar to 3 yr. None of the stars in our sample exhibits RV variations compatible with the presence of Jovian planets with periods shorter than the survey duration. The resulting average frequency of gas giants orbiting metal-poor dwarfs with -2.0 less than or similar to[Fe/H]less than or similar to -0.6 is f(p) < 0.67% (at the 1 sigma confidence level). We examine the implications of this null result in the context of the observed correlation between the rate of occurrence of giant planets and the metallicity of their main-sequence solar-type stellar hosts. By combining our data set with the Fischer & Valenti (2005) uniform sample, we confirm that the likelihood of a star to harbor a planet more massive than Jupiter within 2 AU is a steeply rising function of the host's metallicity. However, the data for stars with -1.0 less than or similar to[Fe/H]less than or similar to 0.0 are compatible, in a statistical sense, with a constant occurrence rate fp similar or equal to 1%. Our results can usefully inform theoretical studies of the process of giant-planet formation across two orders of magnitude in metallicity.

The collapse and fragmentation of initially prolate and oblate, magnetic molecular clouds is calculated in three dimensions with a gravitational, radiative hydrodynamics code. The code includes magnetic field effects in an approximate manner: magnetic pressure, tension, braking, and ambipolar diffusion are all modeled. The parameters varied for both the initially prolate and oblate clouds are the initial degree of central concentration of the radial density profile, the initial angular velocity, and the efficiency of magnetic braking (represented by a factor f(mb) = 10(-4) or 10(-3)). The oblate cores all collapse to form rings that might be susceptible to fragmentation into multiple systems. The outcome of the collapse of the prolate cores depends strongly on the initial density profile. Prolate cores with central densities 20 times higher than their boundary densities collapse and fragment into binary or quadruple systems, whereas cores with central densities 100 times higher collapse to form single protostars embedded in bars. The inclusion of magnetic braking is able to stifle protostellar fragmentation in the latter set of models, as when identical models were calculated without magnetic braking, those cores fragmented into binary protostars. These models demonstrate the importance of including magnetic fields in studies of protostellar collapse and fragmentation, and suggest that even when magnetic fields are included, fragmentation into binary and multiple systems remains as a possible outcome of protostellar collapse.

The supernova injection model for the origin of the short-lived radionuclides (SLRs) in the early solar system is reviewed. First, the meteoritic evidence supporting the model is discussed. Based on the presence of Fe-60 it is argued that a supernova must have been in close proximity to the nascent Solar System. Then, two models of supernova injection, the supernova trigger model and the aerogel model, are described in detail. Both these injection model provide a mechanism for incorporating SLRs into the early solar system. Following this, the mechanisms present in the disk to homogenize the freshly injected radionuclides, and the timescales associated with these mechanisms, are described, It is shown that the SLRs can be homogenized on very short timescales, from a thousand years up to similar to 1 million years. Finally, the SLR ratios expected from a supernova injection are compared to the ratios measured in meteorites. A single supernova can inject enough radionuclides to explain the radionuclide abundances present in the early solar system. (C) 2009 Elsevier Ltd. All rights reserved.

We are undertaking an astrometric search for gas giant planets and brown dwarfs orbiting nearby low-mass dwarf stars with the 2.5 m du Pont Telescope at the Las Campanas Observatory in Chile. We have built two specialized astrometric cameras, the Carnegie Astrometric Planet Search Cameras (CAPSCam-S and CAPSCam-N), using two Teledyne HAWAII-2RG HyViSI arrays, with the cameras' design having been optimized for high-accuracy astrometry of M dwarf stars. We describe two independent CAPSCam data reduction approaches and present a detailed analysis of the observations to date of one of our target stars, NLTT 48256. Observations of NLTT 48256 taken since 2007 July with CAPSCam-S imply that astrometric accuracies of around 0.3 mas hr(-1) are achievable, sufficient to detect a Jupiter-mass companion orbiting 1 AU from a late M dwarf 10 pc away with a signal-to-noise ratio (S/N) of about 4. We plan to follow about 100 nearby (primarily within about 10 pc) low-mass stars, principally late M, L, and T dwarfs, for 10 yr or more, in order to detect very low-mass companions with orbital periods long enough to permit the existence of habitable, Earth-like planets on shorter-period orbits. These stars are generally too faint and red to be included in ground-based Doppler planet surveys, which are often optimized for FGK dwarfs. The smaller masses of late M dwarfs also yield correspondingly larger astrometric signals for a given mass planet. Our search will help to determine whether gas giant planets form primarily by core accretion or by disk instability around late M dwarf stars.

Our team is carrying out a multi-year observing program to directly image and characterize young extrasolar planets using the Near-Infrared Coronagraphic Imager (NICI) on the Gemini-South 8.1-meter telescope. NICI is the first instrument on a large telescope designed from the outset for high-contrast imaging, comprising a high-performance curvature adaptive optics (AO) system with a simultaneous dual-channel coronagraphic imager. Combined with state-of-the-art AO observing methods and data processing, NICI typically achieves approximate to 2 magnitudes better contrast compared to previous ground-based or space-based planet-finding efforts, at separations inside of approximate to 2 ''. In preparation for the Campaign, we carried out efforts to identify previously unrecognized young stars as targets, to develop a rigorous quantitative method for constructing our observing strategy, and to optimize the combination of angular differential imaging and spectral differential imaging. The Planet-Finding Campaign is in its second year, with first-epoch imaging of 174 stars already obtained out of a total sample of 300 stars. We describe the Campaign's goals, design, target selection, implementation, on-sky performance, and preliminary results. The NICI Planet-Finding Campaign represents the largest and most sensitive imaging survey to date for massive (greater than or similar to 1 M-Jup) planets around other stars. Upon completion, the Campaign will establish the best measurements to date on the properties of young gas-giant planets at greater than or similar to 5-10 AU separations. Finally, Campaign discoveries will be well-suited to long-term orbital monitoring and detailed spectrophotometric followup with next-generation planet-finding instruments.

We present an analysis of three years of precision radial velocity measurements of 160 metal-poor stars observed with Keck/HIRES. We report on variability and long-term velocity trends for each star in our sample. We identify several long-term, low-amplitude radial-velocity variables worthy of follow-up with direct imaging techniques. We place lower limits on the detectable companion mass as a function of orbital period. None of the stars in our sample exhibits radial-velocity variations compatible with the presence of Jovian planets with periods shorter than the survey duration (3 yr). The resulting average frequency of gas giants orbiting metal-poor dwarfs with -2.0 <=[Fe/H]<= -0.6 is f(p) < 0.67%. By combining our dataset with the Fischer & Valenti (2005) uniform sample, we confirm that the likelihood of a star to harbor a planet more massive than Jupiter within 2 AU is a steeply rising function of the host's metallicity. However, the data for stars with -1.0 <=[Fe/H]<= 0.0 are compatible, in a statistical sense, with a constant occurrence rate f(p) similar or equal to 1%. Our results usefully inform theoretical studies of the process of giant planet formation across two orders of magnitude in metallicity.