We have measured the chemical composition of 14 stars in the Sagittarius dwarf spheroidal galaxy (Sgr dSph) using high S/N Keck HIRES echelle spectra. For the Sgr dSph stars with [Fe/H]>=-1 the abundances are highly unusual, showing a striking enhancement in heavy s-process elements, increasing with [Fe/H], deficiencies of the a-elements (O, Si, Ca, and Ti), deficiencies of Al and Na, and deficiencies of the odd-numbered iron-peak elements Mn and Cu. Our abundances suggest that the composition of the metal-rich Sgr dSph stars is dominated by the ejecta of an old, metal-poor population, including products of AGB stars and type Ia supernovae (SN).

We present the first results of a new abundance survey of the MilkyWay bulge based on Keck HIRES spectra of 27 K giants in the Baade'sWindow (l = 1 degrees, b= -4 degrees) field. The spectral data used in this study are of much higher resolution and signal-to noise ratio than previous optical studies of Galactic bulge stars. The [Fe/H] values of our stars, which range between -1.29 and + 0.51, were used to recalibrate large low-resolution surveys of bulge stars. Our best value for the mean [Fe/H] of the bulge is -0.10 +/- 0.04. This mean value is similar to the mean metallicity of the local disk and indicates that there cannot be a strong metallicity gradient inside the solar circle. The metallicity distribution of stars confirms that the bulge does not suffer from the so-called G dwarf problem. This paper also details the new abundance techniques necessary to analyze very metal-rich K giants, including a new Fe line list and regions of low blanketing for continuum identification.

We present u'g'r'i'BV photometry and optical spectroscopy of the Type Ib/Ic SN 2005bf covering the first similar to 100 days following discovery. The u'g'BV light curves displayed an unprecedented morphology among Type Ib/Ic supernovae, with an initial maximum some 2 weeks after discovery and a second, main maximum about 25 days after that. The bolometric light curve indicates that SN 2005bf was a remarkably luminous event, radiating at least 6.3 x 10(42) ergs s(-1) at maximum light and a total of 2.1 x 10(49) ergs during the first 75 days after the explosion. Spectroscopically, SN 2005bf underwent a unique transformation from a Type Ic-like event at early times to a typical Type Ib supernova at later phases. The initial maximum in u'g'BV was accompanied by the presence in the spectrum of high-velocity (> 14,000 km s(-1)) absorption lines of Fe II, Ca II, and H I. The photospheric velocity derived from spectra at early epochs was below 10,000 km s(-1), which is unusually low compared with ordinary Type Ib supernovae. We describe one-dimensional computer simulations that attempt to account for these remarkable properties. The most favored model is that of a very energetic (2 x 10(51) ergs), asymmetric explosion of a massive ( 8.3 M-circle dot) Wolf-Rayet WN star that had lost most of its hydrogen envelope. We speculate that an unobserved relativistic jet was launched producing a two-component explosion consisting of ( 1) a polar explosion containing a small fraction of the total mass and moving at high velocity and ( 2) the explosion of the rest of the star. At first, only the polar explosion is observed, producing the initial maximum and the high-velocity absorption-line spectrum resembling a Type Ic event. At late times, this fast- moving component becomes optically thin, revealing the more slowly moving explosion of the rest of the star and transforming the observed spectrum to that of a typical Type Ib supernova. If this scenario is correct, then SN 2005bf is the best example to date of a transition object between normal Type Ib/Ic supernovae and gamma-ray bursts.

We have carried out a detailed abundance analysis using high-dispersion spectra from HIRES at Keck for a sample of 16 carbon stars found among candidate extremely metal-poor (EMP) stars from the Hamburg/ESO Survey (HES). We find that the Fe metallicities for the cooler C stars (T-eff similar to 5100 K) have been underestimated by a factor of similar to 10 by the standard HES tools. The results presented here provided crucial supporting data used recently by Cohen et al. to derive the frequency of C stars among EMP stars. C enhancement in these EMP C stars appears to be independent of Fe metallicity and approximately constant at similar to 1/5 the solar epsilon(C). The C enhancement shows some evidence of decreasing with decreasing T-eff (increasing luminosity), presumably due to mixing and dredge-up of C-depleted material. The mostly low C-12/C-13 ratios (similar to 4) and the high N abundances in many of these stars suggest that material that has been through proton burning via the CN cycle comprises most of the stellar envelope. C enhancement in this sample is associated with strong enrichment of heavy nuclei beyond the Fe peak for 12 of the 16 stars. The remaining C stars from the HES, which tend to be the most Fe-poor, show no evidence for enhancement of the heavy elements. Very high enhancements of lead are detected in some of the C stars with highly enhanced Ba. The strong lead lines, the high Ba/Eu ratios, and the high ratios of abundances of the diagnostic elements in the first and second s-process peaks demonstrate that the s-process is responsible for the enhancement of the heavy elements for the majority of the C stars in our sample. The low C-12/C-13 ratios and large C and N enhancements of the EMP C stars are more extreme than those of intrinsic asymptotic giant branch C stars of near-solar Fe metallicity, but closer to the composition of CH stars. Our subsample of EMP C stars without s-process enhancement is reminiscent of the R-type C stars in the solar neighborhood; thus, we expect that they are formed by similar mechanisms. We suggest that both the s-process-enhanced and Ba-normal C stars result from phenomena associated with mass transfer in binary systems. This leads directly to the progression from C stars to CH stars and then to Ba stars as the Fe metallicity increases.

We present an abundance analysis for the extremely metal-poor (EMP) star HE 1424-0241 based on high dispersion spectra from HIRES at Keck. This star is a giant on the lower red giant branch with [Fe/H] similar to -4.0 dex. Relative to Fe, HE 1424-0241 has normal Mg, but it shows a very large deficiency of Si, with is an element of(Si)/is an element of(Fe) similar to and that of all previously known EMP giants or dwarfs. It also has a moderately large 1/10 is an element of(Si)/is an element of(Mg) similar to 1/25 deficiency of Ca and a smaller deficit of Ti, combined with enhanced Mn and Co and normal or low C. We suggest that in HE 1424-0241 we see the effect of a very small number of contributing supernovae, and that the SNe II contributing to the chemical inventory of HE 1424-0241 were biased in progenitor mass or in explosion characteristics so as to reproduce its abnormal extremely low Si/Mg ratio. HE 1424-0241 shows a deficiency of the explosive alpha-burning elements Si, Ca, and Ti coupled with a ratio [Mg/Fe] normal for EMP stars; Mg is produced via hydrostatic alpha-burning. The latest models of nucleosynthesis in SNe II fail to reproduce the abundance ratios seen in HE 1424-0241 for any combination of the parameter space of core-collapse explosions they explore.

We report detailed abundances of O, Na, Mg, Al, Si, Ca, and Ti - elements produced by massive stars - for 27 red giants toward the Galactic bulge in Baade's window. These species are overabundant in the bulge relative to the disk, consistent with enhancement by Type II SN ejecta. Mg/Fe = +0.3 dex over the full range of [Fe/H], while O, Si, Ca, and Ti are elevated but follow more disklike trends. We propose that the decline in [O/Fe] is due to metallicity-dependent oxygen yields from massive stars, perhaps connected with the Wolf-Rayet phenomenon. The elements Si, Ca, and Ti, believed to be produced during explosive nucleosynthesis, possess identical trends with [Fe/H]. We attribute the decline of these elements to metallicity-dependent yields in Type II SNe. The trend of [Al/ Fe] is found to vary strikingly with environment; the range from the Sgr dwarf to the bulge is 0.7 dex. The disjoint composition of the thick/thin disk and bulge stars is inconsistent with models in which the bulge formed from the thickening of the disk, while the elevated alpha elements are consistent with a rapid bulge formation timescale. The starkly smaller scatter of [< SiCaTi >/Fe] with [Fe/H] in the bulge compared with the halo is consistent with the expectation that the bulge should have efficiently mixed. The metal-poor bulge [< SiCaTi >/Fe] ratios are higher than similar to 80% of the halo; the bulge could not have formed from gas with the present-day halo composition.

We report precipitable water vapor (PWV) measurements made at Las Campanas Observatory using optical spectra of H2O lines obtained with the Magellan echelle spectrograph, and calculated using a robust technique that is accurate to 5%-10%. Calibration of the relationship between our PWV measurements and opacity values at 225 GHz was made possible by simultaneous observations with a tipping radiometer. Based on this calibration, we present Las Campanas Observatory wintertime precipitable water vapor statistics, measured using the tipping radiometer, during a 1.5 month campaign. The median value of 2.8 +/- 0.3 mm is consistent with that measured at the nearby La Silla Observatory during the VLT site survey. We conclude that in the Southern hemisphere winter months, we can expect good conditions for infrared observing (less than or similar to 1.5 mm) approximately 10% of the time at Las Campanas Observatory.

We report on the calibration of the relationship between precipitable water vapor and opacity at 225 GHz at Las Campanas Observatory as measured by a Tipping Radiometer. This relationship is a function of altitude and temperature and thus is highly dependent on location. We determine the relationship applicable at Las Campanas Observatory by using high-resolution Magellan Echelle spectra to measure the precipitable water vapor independently and absolutely. Temperature insensitive (between 220-300 K) lines allow the use of a single temperature atmospheric model as long as the lines are unsaturated. Absolute calibration was achieved by measuring the humidity in the path length of the McMath Solar telescope with a psycrometer [1]. We have expanded the method presented by Brault et al. (1975) with improved partition functions and additional lines. Based on this calibration, we present Southern hemisphere winter-time precipitable water vapor statistics for Las Campanas Observatory as measured during a two month campaign. We find that the median winter value of 2.8 +/- 0.3 mm is consistent with that measured at the nearby La Silla Observatory during the VLT site survey [21 and inconsistent (lower by a factor of approximately two) with estimates, also for La Silla, derived from GOES-8 satellite imagery and the European Centre for Medium-Range Weather Forecasting (ECMWF) meteorological numerical model 13]. Furthermore, in the Southern hemisphere winter months, we can expect good conditions for infrared observing (less than or similar to 1.5 mm) at the tenth percentile level. Further details can be found in Thomas-Osip et al. [4].

We present a detailed abundance analysis based on high-resolution and high signal-to-noise spectra of eight extremely metal-poor ( EMP) stars with [Fe/H] less than or similar to 3.5 dex, four of which are new. Only stars with 4900 K < T-eff < 5650 K are included. Two stars of the eight are outliers in each of several abundance ratios. The most metal-poor star in this sample, HE 1424-0241, has [Fe/H] similar to -4 dex and is thus among the most metal-poor stars known in the Galaxy. It has highly anomalous abundance ratios unlike those of any other known EMP giant, with very low Si, Ca, and Ti relative to Fe, and enhanced Mn and Co, again relative to Fe. Only ( low) upper limits for C and N can be derived from the nondetection of the CH and NH molecular bands. HE 0132-2429, another sample star, has excesses of N and Sc with respect to Fe. The strong outliers in abundance ratios among the Fe-peak elements in these C-normal stars, not found at somewhat higher metallicities ([Fe/H] similar to -3 dex), are definitely real. They suggest that at such low metallicities we are beginning to see the anticipated and long sought stochastic effects of individual supernova events contributing to the Fe-peak material within a single star. With spectra reaching well into the near-UV we are able to probe the behavior of copper abundances in such extreme EMP stars. A detailed comparison of the results of the analysis procedures adopted by our 0Z project compared to those of the First Stars VLT Large Project finds a systematic difference for [Fe/H] of similar to 0.3 dex, our values always being higher.

We present chemical abundances for O, Na, Mg, Al, Si, Ca, Ti, and Fe in eight red giants and one turnoff star in the metal-rich globular cluster 47 Tuc, based on spectroscopy with the Magellan Inamori Kyocera Echelle high-resolution spectrograph on the Magellan 6.5 m Clay telescope. A robust line by a line differential abundance analysis technique, relative to the K-giant Arcturus, was used to reduce systematic errors from atmospheric and atomic parameters. Our derived mean LTE [Fe/H] of -0.76 +/- 0.01 +/- 0.04 dex (random and systematic error, respectively) is more metal poor by about 0.1 dex than recent literature results. The chemical element ratios in this nearby globular cluster most closely resemble those of the Galactic bulge, although there is a non-negligible overlap with the composition of thick-disk stars. We find that the [Al/Fe] and [Na/Fe] ratios coincide with the upper boundary of the trends seen in the bulge and thick disk. There is only a small intrinsic scatter in the majority of the abundance ratios, indicating that 47 Tuc is mostly a rather chemically homogeneous system.