Eclipsing binary stars in the Large and Small Magellanic Clouds from the MACHO project: The Sample

We present a new sample of 4634 eclipsing binary stars in the Large Magellanic Cloud (LMC), expanding on a previous sample of 611 objects and a new sample of 1509 eclipsing binary stars in the Small Magellanic Cloud (SMC), that were identified in the light curve database of the MACHO project. We perform a cross correlation with the OGLE-II LMC sample, finding 1236 matches. A cross correlation with the OGLE-II SMC sample finds 698 matches. We then compare the LMC subsamples corresponding to center and the periphery of the LMC and find only minor differences between the two populations. These samples are sufficiently large and complete that statistical studies of the binary star populations are possible.Comment: 67 pages, 40 figure

The Keck+Magellan Survey for Lyman Limit Absorption II: A Case Study on Metallicity Variations

We present an absorption line analysis of the Lyman limit system (LLS) at z=3.55 in our Magellan/MIKE spectrum of PKS2000-330. Our analysis of the Lyman limit and full HI Lyman series constrains the total HI column density of the LLS (N_HI = 10^[18.0 +/- 0.25] cm^{-2} for b_HI >= 20 km/s) and also the N_HI values of the velocity subsystems comprising the absorber. We measure ionic column densities for metal-line transitions associated with the subsystems and use these values to constrain the ionization state (>90% ionized) and relative abundances of the gas. We find an order of magnitude dispersion in the metallicities of the subsystems, marking the first detailed analysis of metallicity variations in an optically thick absorber. The results indicate that metals are not well mixed within the gas surrounding high $z$ galaxies. Assuming a single-phase photoionization model, we also derive an N_H-weighted metallicity, = -1.66 +/- 0.25, which matches the mean metallicity in the neutral ISM in high z damped Lya systems (DLAs). Because the line density of LLSs is ~10 times higher than the DLAs, we propose that the former dominate the metal mass-density at z~3 and that these metals reside in the galaxy/IGM interface. Considerations of a multi-phase model do not qualitatively change these conclusions. Finally, we comment on an anomalously large O^0/Si^+ ratio in the LLS that suggests an ionizing radiation field dominated by soft UV sources (e.g. a starburst galaxy). Additional abundance analysis is performed on the super-LLS systems at z=3.19.Comment: 20 pages, 7 figures (most in color). Accepted to Ap

Super-Solar Super Lyman Limit Systems

We present abundance measurements for two super Lyman Limit systems (SLLS; quasar absorption line systems with 10^19 cm^-2 < N_HI < 10^20.3 cm^-2) selected from a set of metal-strong absorbers in the Sloan Digital Sky Survey quasar database. After applying estimate corrections for photoionization effects, we derive gas-phase metallicities of [M/H]=+0.7 +/- 0.2 dex for the SLLS at z=1.7749 toward SDSS0927+5621 and [M/H]=+0.05 +/- 0.1 dex for the SLLS at z=1.7678 toward SDSS0953+5230. The former exhibits among the highest gas metallicity of any astrophysical environment and its total metal surface density exceeds that of nearly every known damped Lya system. The properties of these absorbers -- high metallicity and large velocity width (> 300 km/s) -- resemble those of gas observed in absorption in the spectra of bright, star-forming galaxies at high redshift. We discuss the metal mass density of the SLLS based on these observations and our ongoing SLLS survey and argue that a conservative estimate to the total metal budget at z=2 is greater than 15% of the total, suggesting that the metal-rich LLS may represent the dominant metal reservoir in the young universe.Comment: 6 pages, 2 figures. Submitted to ApJL; Revised June 22, 200