We present measurements of galaxy-galaxy weak lensing from 225 deg(2) of early commissioning imaging data from the Sloan Digital Sky Survey (SDSS). We measure a mean tangential shear around a stacked sample of foreground galaxies in three bandpasses (g', r', and i') out to angular radii of 600", detecting the shear signal at very high statistical significance. The shear profile is well described by a power law gamma(T) = gamma(TO)(1/theta)", with best-fit slope of eta = 0.7-1.1 (95% confidence). In the range theta = 10"-600", the mean tangential shear is approximately 6 +/- 1 x 10(-4) in all three bands. A variety of rigorous tests demonstrate the reality of the gravitational lensing signal and confirm the uncertainty estimates. In particular, we obtain shear measurements consistent with zero when we rotate the background galaxies by 45 degrees, replace foreground galaxies with random points, or replace foreground galaxies with bright stars. We interpret our results by assuming that all matter correlated with galaxies belongs to the galaxies. We model the mass distributions of the foreground glaxies, which have a mean luminosity [L(theta < 5")] = 8.7 +/- 0.7 x 10(9) h(-2) L-g'circle dot,1.4 +/- 0.12 x 10(10) h(-2) L-r'circle dot, 1.8 +/- 0.14 x 10(10) h(-2) L-i'circle dot, as approximately isothermal spheres characterized by a velocity dispersion a, and a truncation radius s. The velocity dispersion is constrained to be sigma(v) = 150-190 km s(-1) at 95% confidence (145-195 km s(-1) including systematic uncertainties), consistent with previous determinations but with smaller error bars. Our detection of shear at large angular radii sets a 95% confidence lower limit s > 140", corresponding to a physical radius of 260 h(-1) kpc, implying that the dark halos of typical luminous galaxies extend to very large radii. However, it is likely that this is being systematically biased to large value by diffuse matter in the halos of groups and clusters of galaxies. We also present a preliminary determination of the galaxy-mass correlation function, finding a correlation length similar to the galaxy autocorrelation function and consistency with a low matter density universe with modest bias.

The Magellan guider camera uses a low-noise frame transfer CCD with a digital signal processor based controller. The electronics feature a compact, simple design, optimized for fast settling times and rapid readout rate. The camera operates (nominally) at 20 degreesC with thermoelectric cooling. Multiple operating modes are supported, with software selectable binning, exposure times, and subrastering.

Phase transitions and equations of state of the alkaline earth fluorides CaF2, SrF2, and BaF2 were examined by static compression to pressures as high as 146 GPa. Angle-dispersive x-ray diffraction experiments were performed on polycrystalline samples in the laser-heated diamond-anvil cell. We confirmed that at pressures less than 10 GPa all three materials undergo a phase transition from the cubic (Fm (3) over barm) fluorite structure to the orthorhombic (Pnam) cotunnite-type structure. This work has characterized an additional phase transition in CaF2 and SrF2: these materials were observed to transform to a hexagonal (P6(3)/mmc) Ni2In-type structure between 63-79 GPa and 28-29 GPa, respectively, upon laser heating. For SrF2, the Ni2In-type phase was confirmed by Rietveld refinement. Volumes were determined as a function of pressure for all high-pressure phases and fit to the third-order Birch-Murnaghan equation of state. For CaF2 and SrF2, the fluorite-cotunnite transition results in a volume decrease of 8-10 %, while the bulk modulus of the cotunnite-type phase is the same or less than that of the fluorite phase within uncertainty. For all three fluorides, the volume reduction associated with the further transition to the Ni2In-type phase is similar to 5%. The percentage increase in the bulk modulus (Delta K) across the transition is greater when the cation is smaller. While for BaF2, Delta K is 10-30 %, Delta K values for SrF2 and CaF2 are 45-65 % and 20-40 %. Although shock data for CaF2 have been interpreted to show a transition to a highly incompressible phase above 100 GPa, this is not consistent with our static equation of state data.

We present a search for "hypercompact" star clusters in the Milky Way using a combination of Gaia and the Dark Energy Camera Legacy Survey (DECaLS). Such putative clusters, with sizes of similar to 1 pc and containing 500-5000 stars, are expected to remain bound to intermediate-mass black holes (M (BH) approximate to 10(3)-10(5) M (circle dot)) that may be accreted into the Milky Way halo within dwarf satellites. Using the semianalytic model SatGen, we find an expected similar to 100 wandering intermediate-mass black holes if every infalling satellite hosts a black hole. We do not find any such clusters in our search. Our upper limits rule out 100% occupancy but do not put stringent constraints on the occupation fraction. Of course, we need stronger constraints on the properties of the putative star clusters, including their assumed sizes and the fraction of stars that would be compact remnants.