Optimal extraction of quasar Lyman limit absorption systems from the IUE archive

The IUE archive contains a wealth of information on Lyman limit absorption systems (LLS) in quasar spectra. QSO spectra from the IUE data base were optimally extracted, coadded, and analyzed to yield a homogeneous samples of LLS at low red shifts. This sample comprise 36 LLS, twice the number previously analyzed low z samples. These systems are ideal for the determination of the origin, redshift evolution, ionization, velocity dispersions and the metal abundances of absorption systems. Two of them are also excellent targets for the primordial Deuterium to Hydrogen ratio

Strong associated C 4 absorption in low redshift quasars

IUE spectra of quasars were used to determine the frequency of occurrence of strong associated C 4 absorption systems at low red shifts. Four systems are found with rest frame equivalent width (REW) greater than 5 angstroms in the spectra of 38 quasars. This rate of occurrence of 0.12 is not significantly different from the rate of 0.064 determined for high red shift quasars. The detected strong associated systems are all in low red shift quasars which have been imaged from the ground. One of the quasars is unusual, having two nuclei, a close companion and distorted isotopes. Two of the others also have close companion galaxies at projected distances of under 100 kpc. The conclusion was made that a much larger sample is needed

The Neutral Hydrogen Column Density towards Q1937--1009 from the Unabsorbed Intrinsic Continuum in the Lyman-α\alpha Forest

The absorption system at $z=3.572$ towards Q1937--1009 provides the best extragalactic measurement of the atomic deuterium to hydrogen ratio, D/H. We have obtained a new low-resolution, high signal-to-noise ratio (SNR) Keck spectrum to re-measure the total neutral hydrogen column density N(H I) using the amount of Lyman continuum absorption. We develop a new method to directly determine the intrinsic unabsorbed quasar continuum from low-resolution spectra of the \Lya forest for the first time. We use three types of spectra to measure N(H I): (1) A wide slit spectrum for flux calibration, (2) a high-resolution spectrum to determine the unabsorbed continuum between \Lya forest lines, and (3) a high SNR spectrum to measure the residual flux below the Lyman limit. We measure Log [N(H I)] = 17.86 $\pm$ 0.02 \cm2, which is reliable because N(H I) is fully specified by the data. This result is consistent with the N(H I) measured by Tytler, Fan & Burles (1996) from the Lyman series absorption lines, but not with absorption models proposed by Wampler (1996) nor estimates of the total N(H I) by Songaila et al. (1997), both of which suggested lower N(H I) and higher D/H. The Wampler models predict abundant flux below the Lyman limit which is absent from both our old and new spectra, taken with different instruments. The new Keck data is consistent with the data presented by Songaila et al. (1997). The results differ due to the different methods of analysis, and our measurement of the QSO continuum does not agree with the continuum models assumed by Songaila et al. (1997).Comment: 15 pages, 6 figures, To appear in the Astronomical Journal in October 199