The Sloan Digital Sky Survey (SDSS) has validated and made publicly available its Second Data Release. This data release consists of 3324 deg(2) of five-band (ugriz) imaging data with photometry for over 88 million unique objects, 367,360 spectra of galaxies, quasars, stars, and calibrating blank sky patches selected over 2627 deg(2) of this area, and tables of measured parameters from these data. The imaging data reach a depth of r approximate to 22.2 ( 95% completeness limit for point sources) and are photometrically and astrometrically calibrated to 2% rms and 100 mas rms per coordinate, respectively. The imaging data have all been processed through a new version of the SDSS imaging pipeline, in which the most important improvement since the last data release is fixing an error in the model fits to each object. The result is that model magnitudes are now a good proxy for point-spread function magnitudes for point sources, and Petrosian magnitudes for extended sources. The spectroscopy extends from 3800 to 9200 8 at a resolution of 2000. The spectroscopic software now repairs a systematic error in the radial velocities of certain types of stars and has substantially improved spectrophotometry. All data included in the SDSS Early Data Release and First Data Release are reprocessed with the improved pipelines and included in the Second Data Release. Further characteristics of the data are described, as are the data products themselves and the tools for accessing them.

We present the full spectroscopic white dwarf and hot subdwarf sample from the Sloan Digital Sky Survey (SDSS) first data release, DR1. We find 2551 white dwarf stars of various types, 240 hot subdwarf stars, and an additional 144 objects we have identified as uncertain white dwarf stars. Of the white dwarf stars, 1888 are nonmagnetic DA types and 171 are nonmagnetic DBs. The remaining ( 492) objects consist of all different types of white dwarf stars: DO, DQ, DC, DH, DZ, hybrid stars such as DAB, etc., and those with nondegenerate companions. We fit the DA and DB spectra with a grid of models to determine the T-eff and log g for each object. For all objects, we provide coordinates, proper motions, SDSS photometric magnitudes, and enough information to retrieve the spectrum/image from the SDSS public database. This catalog nearly doubles the known sample of spectroscopically identified white dwarf stars. In the DR1 imaged area of the sky, we increase the known sample of white dwarf stars by a factor of 8.5. We also comment on several particularly interesting objects in this sample.

We utilize Sloan Digital Sky Survey imaging and spectroscopy of similar to 53,000 star-forming galaxies at z similar to 0.1 to study the relation between stellar mass and gas-phase metallicity. We derive gas-phase oxygen abundances and stellar masses using new techniques that make use of the latest stellar evolutionary synthesis and photoionization models. We find a tight (+/- 0.1 dex) correlation between stellar mass and metallicity spanning over 3 orders of magnitude in stellar mass and a factor of 10 in metallicity. The relation is relatively steep from 10(8.5) to 10(10.5) M-. h(70)(-2), in good accord with known trends between luminosity and metallicity, but flattens above 10(10.5) M-.. We use indirect estimates of the gas mass based on the Halpha luminosity to compare our data to predictions from simple closed box chemical evolution models. We show that metal loss is strongly anticorrelated with baryonic mass, with low-mass dwarf galaxies being 5 times more metal depleted than L* galaxies at z similar to 0.1. Evidence for metal depletion is not confined to dwarf galaxies but is found in galaxies with masses as high as 10(10) M-.. We interpret this as strong evidence of both the ubiquity of galactic winds and their effectiveness in removing metals from galaxy potential wells.

The f/5 instrumentation suite for the Clay telescope was developed to provide the Magellan Consortium observer community with wide field optical imaging and multislit NIR spectroscopy capability. The instrument suite consists of several major subsystems including two focal plane instruments. These instruments are Megacam and MMIRS. Megacam is a panoramic, square format CCD mosaic imager, 0.4 degrees on a side. It is instrumented with a full set of Sloan filters. MMIRS is a multislit NIR spectrograph that operates in Y through K band and has long slit and imaging capability as well. These two instruments can operate both at Magellan and the MMT. Megacam requires a wide field refractive corrector and a Topbox to support shutter and filter selection functions, as well as to perform wavefront sensing for primary mirror figure correction. Both the corrector and Topbox designs were modeled on previous designs for MMT, however features of the Magellan telescope required considerable revision of these designs. In this paper we discuss the optomechanical, electrical, software and structural design of these subsystems, as well as operational considerations that attended delivery of the instrument suite to first light.

We present the design and performance of the multi-object fiber spectrographs for the Sloan Digital Sky Survey (SDSS) and their upgrade for the Baryon Oscillation Spectroscopic Survey (BOSS). Originally commissioned in Fall 1999 on the 2.5 m aperture Sloan Telescope at Apache Point Observatory, the spectrographs produced more than 1.5 million spectra for the SDSS and SDSS-II surveys, enabling a wide variety of Galactic and extra-galactic science including the first observation of baryon acoustic oscillations in 2005. The spectrographs were upgraded in 2009 and are currently in use for BOSS, the flagship survey of the third-generation SDSS-III project. BOSS will measure redshifts of 1.35 million massive galaxies to redshift 0.7 and Ly alpha absorption of 160,000 high redshift quasars over 10,000 deg(2) of sky, making percent level measurements of the absolute cosmic distance scale of the universe and placing tight constraints on the equation of state of dark energy. The twin multi-object fiber spectrographs utilize a simple optical layout with reflective collimators, gratings, all-refractive cameras, and state-of-the-art CCD detectors to produce hundreds of spectra simultaneously in two channels over a bandpass covering the near-ultraviolet to the near-infrared, with a resolving power R = lambda/FWHM similar to 2000. Building on proven heritage, the spectrographs were upgraded for BOSS with volume-phase holographic gratings and modern CCD detectors, improving the peak throughput by nearly a factor of two, extending the bandpass to cover 360 nm < lambda < 1000 nm, and increasing the number of fibers from 640 to 1000 per exposure. In this paper we describe the original SDSS spectrograph design and the upgrades implemented for BOSS, and document the predicted and measured performances.

In the interstellar medium (ISM), molecular hydrogen is expected to form almost exclusively on the surfaces of dust grains. Due to that molecule's large formation energy (-4.5 eV), several dynamical effects are likely associated with the process, including the alignment of asymmetric dust grains with the ambient magnetic field. Such aligned dust grains are, in turn, believed to cause the broadband optical/infrared polarization observed in the ISM. Here, we present the first observational evidence for grain alignment driven by H-2 formation, by showing that the polarization of the light from stars behind the reflection nebula IC 63 appears to correlate with the intensity of H-2 fluorescence. While our results strongly suggest a role for "Purcell rockets" in grain alignment, additional observations are needed to conclusively confirm their role. By showing a direct connection between H-2 formation and a probe of the dust characteristics, these results also provide one of the first direct confirmations of the grain-surface formation of H-2. We compare our observations to ab initio modeling based on Radiative Torque Alignment (RAT) theory.

The GMT-Consortium Large Earth Finder (G-CLEF) will be part of the first generation instrumentation suite for the Giant Magellan Telescope (GMT). G-CLEF will be a general purpose optical passband echelle spectrograph with a precision radial velocity (PRV) capability of 10 cm/sec, a requirement necessary for the detection of Earth analogues. The instrument will be particularly sensitive to thermal effects and the necessary stability cannot be achieved through the use of low CTE materials alone. It is the combination of low CTE materials and exquisite thermal control which will enable the instrument to achieve its precision requirements.

Transition metal borides are known due to their attractive mechanical, electronic, refractive, and other properties. A new class of rhenium borides was identified by synchrotron single-crystal X-ray diffraction experiments in laser-heated diamond anvil cells between 26 and 75 GPa. Recoverable to ambient conditions, compounds rhenium triboride (ReB3) and rhenium tetraboride (ReB4) consist of close-packed single layers of rhenium atoms alternating with boron networks built from puckered hexagonal layers, which link short bonded (similar to 1.7 angstrom) axially oriented B-2 dumbbells. The short and incompressible Re-B and B-B bonds oriented along the hexagonal c-axis contribute to low axial compressibility comparable with the linear compressibility of diamond. Sub-millimeter samples of ReB3 and ReB4 were synthesized in a large-volume press at pressures as low as 33 GPa and used for material characterization. Crystals of both compounds are metallic and hard (Vickers hardness, H-V = 34(3) GPa). Geometrical, crystal-chemical, and theoretical analysis considerations suggest that potential ReBx compounds with x > 4 can be based on the same principle of structural organization as in ReB3 and ReB4 and possess similar mechanical and electronic properties.

Following our discovery of 2001 QT(297) as the second known binary Edgeworth - Kuiper Belt Object (EKBO) in October of 2001 [IAUC 7733], we have carried out additional high spatial resolution ground based imaging in October and November of 2001 and July, August, and September of 2002. Using the Raymond and Beverly Sackler Magellan Instant Camera (MagIC) on the Baade and Clay 6.5 m telescopes at Las Campanas Observatory in Chile, we have obtained accurate astrometric and photometric measurements in the Sloan r', i', and g' filters. Superb seeing conditions and PSF fitting allow an accurate determination of the binary component separation and position angle over time as well as a detailed study of color and temporal variability of the individual components. Here we present a physical characterization of the individual components of 2001 QT297 based on these astrometric, color and variability measurements. We find the primary to exhibit colors about 0.3 magnitudes redder than solar with no evidence for variability. The secondary component, however, exhibits strong variability (similar to0.6 magnitudes) with a best fit period of 4.7526 +/- 0.0007 h for a single peak lightcurve or 9.505 +/- 0.001 h for a dual peaked lightcurve. The colors measured for the secondary also suggest variability. Based on a preliminary orbit fit for the pair using observations spanning a one year arc, we are able to estimate a system mass of similar to 3.2 x 10(18) kg and provide constraints to the surface albedo of 9-14% for assumed densities between 1 and 2 g/cm(3).

We present Keck/NIRSPEC near-IR images and Magellan/IMACS optical spectroscopy of the host galaxy of GRB 031203. The host is an actively star-forming galaxy at z=0.1055+/-0.0001. This is the lowest redshift GRB to date, aside from GRB 980425. From the hydrogen Balmer lines, we infer an extinction of A(V)=3.62+/-0.25 or a total reddening E-T (B-V)=1.17+/-0.1 toward the sight line to the nebular regions. After correcting for reddening, we perform an emission-line analysis and derive an ISM temperature of T =13400+/-2000 K and electron density of n(e)=300 cm(-3). These imply a metallicity [O/H]=-0.72+/-0.15 dex and a roughly solar abundance pattern for N, Ne, S, and Ar. Integrating Halpha, we infer a dust-corrected star formation rate (SFR) of more than 11 M-circle dot yr(-1). These observations have the following implications: (1) The galaxy has a low K'-band luminosity Lapproximate toL*(K)/5, typical of GRB host galaxies. (2) The low redshift indicates GRB 031203 had an isotropic-equivalent gamma-ray energy release smaller than all previous confirmed GRB events. The burst discovery raises the likelihood of identifying many additional low-z, low-flux events with Swift. (3) The large SFR, low metallicity, and inferred hard radiation field are suggestive of massive star formation, supporting the collapsar model. (4) Several lines of evidence argue against the identification of GRB 031203 as an X-ray flash event.