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We present the results of a MgII absorption-line survey using QSO spectra from the SDSS EDR. Over 1,300 doublets with rest equivalent widths greater than 0.3\AA and redshifts $0.366 \le z \le 2.269$ were identified and measured. We find that the $\lambda2796$ rest equivalent width ($W_0^{\lambda2796}$) distribution is described very well by an exponential function $\partial N/\partial W_0^{\lambda2796} = \frac{N^*}{W^*} e^{-\frac{W_0}{W^*}}$, with $N^*=1.187\pm0.052$ and $W^*=0.702\pm0.017$\AA. Previously reported power law fits drastically over-predict the number of strong lines. Extrapolating our exponential fit under-predicts the number of $W_0 \le 0.3$\AA systems, indicating a transition in $dN/dW_0$ near $W_0 \simeq 0.3$\AA. A combination of two exponentials reproduces the observed distribution well, suggesting that MgII absorbers are the superposition of at least two physically distinct populations of absorbing clouds. We also derive a new redshift parameterization for the number density of $W_0^{\lambda2796} \ge 0.3$\AA lines: $N^*=1.001\pm0.132(1+z)^{0.226\pm0.170}$ and $W^*=0.443\pm0.032(1+z)^{0.634\pm 0.097}$\AA. We find that the distribution steepens with decreasing redshift, with $W^*$ decreasing from $0.80\pm0.04$\AA at $z=1.6$ to $0.59\pm0.02$\AA at $z=0.7$. The incidence of moderately strong MgII $\lambda2796$ lines does not show evidence for evolution with redshift. However, lines stronger than $\approx 2$\AA show a decrease relative to the no-evolution prediction with decreasing redshift for $z \lesssim 1$. The evolution is stronger for increasingly stronger lines. Since $W_0$ in saturated absorption lines is an indicator of the velocity spread of the absorbing clouds, we interpret this as an evolution in the kinematic properties of galaxies from moderate to low z.

New optical and infrared observations along the sight-line toward the quasar OI 363 (0738+313) are presented and discussed. Excluding systems which lack confirming UV spectroscopic observations of the actual Lyman alpha line, this sight-line presently contains the two lowest-redshift classical damped Lyman alpha (DLA) quasar absorption line systems known (i.e. with N(HI) \ge 2 x 10^{20} atoms cm^{-2}), one at z(abs)=0.0912 and the other at z(abs)=0.2212. The z=0.09 DLA galaxy appears to be an extended low surface brightness galaxy which is easily visible only in infrared images and shows rich morphological structure. Subtraction of the quasar nuclear and host light yields L_K \approx 0.08L_K* at z=0.09. The impact parameter between the galaxy and quasar sight-line is very small, b

We report the discovery of two low redshift HI 21cm absorbers, one at z = 0.2212 towards the z_{em} = 0.630 quasar OI 363 (B0738+313), and the other at z = 0.3127 towards PKS B1127-145 (z_{em} = 1.187). Both were found during a survey of MgII selected systems at redshifts 0.2 < z < 1 using the new UHF-high system at the Westerbork Synthesis Radio Telescope (WSRT). New HST/FOS observations also identify both systems as damped Ly-alpha (DLa) absorbers. By comparing the column density from the DLa line with that from the HI 21cm line, we calculate the spin temperature, and find that T_s is approximately 1000 K for both of these low redshift absorbers. We briefly discuss some implications of this result.

We report the discovery of a high-ionization broad absorption line system at a redshift of z_abs=0.695 in the spectrum of the z_em=1.052 radio-quiet quasar PG 2302+039. Broad absorption with FWHM from 3,000 to 5,000 km/s is detected from C IV, N V, and O VI in HST Faint Object Spectrograph spectra of the quasar. A narrow line system (FWHM approximately 250 km/s) at z_abs=0.7016 is resolved from the broad blend and includes absorption by Ly-alpha and the C IV, N V, and O VI doublets. No absorption by low-ionization metal species (e.g. Si II and Mg II) is detected in the HST or ground-based spectra for either the broad or the narrow system. The centroids of the broad system lines are displaced by approximately 56,000 km/s to the blue of the quasar's broad emission lines. The reddest extent of the broad line absorption is more than 50,000 km/s from the quasar. The properties of this system are unprecedented whether it is an intervening or an ejected system.

The radial distributions of dark matter (DM) density and temperature in Lyα clouds seen in QSO spectra are discussed in the framework of a ‘minihalo’ model. Available observational data on the distribution of Lyα clouds in column density, in combination with assumptions about the hydrostatic equilibrium of DM and gas, and information provided by the equation of state of the gas, provide a reasonable basis for constraining the shapes of the DM density and temperature distributions. The analysis shows that DM density should be strongly peaked at the cloud center, while DM temperature should have a minimum in this region. In the framework of a minihalo model this work leads to the conjecture that an important process in minihalo formation may be some sort of gravitational-thermal instability in the DM gas.

Comparison of the observed properties of damped Lyα absorbers (DLAs) seen in QSO spectra with different structures in the interstellar medium of our own and nearby galaxies shows that these absorbers may be interpreted as giant hydrogen clouds (GHCs) in intervening galaxies along the lines-of-sight. We show that the observational data on the redshift and column density distribution of the DLAs may be used to study the mass spectrum of GHCs and its evolution with cosmic time. The derived mass spectrum may be represented by a power-law relation with rapid cosmic evolution in the exponent. The evolution may be interpreted in terms of global star formation processes in young galaxies.

We present the data and initial results from a combined Hubble Space Telescope (HST)/IUE/ground-based spectroscopic monitoring campaign on the Seyfert 1 galaxy NGC 5548 that was undertaken in order to address questions that require both higher temporal resolution and higher signal-to-noise ratios than were obtained in our previous multiwavelength monitoring of this galaxy in 1988-1989. IUE spectra were obtained once every 2 days for a period of 74 days beginning on 1993 March 14. During the last 39 days of this campaign, spectroscopic observations were also made with the HST Faint Object Spectrograph (FOS) on a daily basis. Ground-based observations, consisting of 165 optical spectra and 77 photometric observations (both CCD imaging and aperture photometry), are reported for the period 1992 October-1993 September, although many of the data are concentrated around the time of the satellite-based program. These data constitute a fifth year of intensive optical monitoring of this galaxy. In this contribution we describe the acquisition and reduction of all of the satellite and ground-based data obtained in this program. We describe in detail various photometric problems with the FOS and explain how we identified and corrected for various anomalies.

Recently, Walsh, Carswell and Weymann1 reported the discovery of two objects (0957+56A,B) with identical spectra and separated by 6 arc min. They suggested that a gravitational lens was responsible. The cumulative result of subsequent work on this object (see refs 2–9) corroborates this interpretation. The example of 0957+56A,B and the data presented here suggest a similar phenomenon is involved in the case of PG1115+08.

Spectroscopy and polarimetry of several very red stars, noted on Near Infrared Photographic Sky Survey photographs in the region of NGC 1333, have yielded a 'map' suggesting the extent of polarization arising from a two-cloud structure in the region. Spectral types and color indices of the stars make it possible to infer that grain radii in the clouds exceed typical interstellar medium values and, further, that they increase with optical depth into the cloud. The present observations indicate that the cloud structure is far more extensive than previously realized.

A list of 103 faint red stars in a 0.7-square-degree area located near NGC 6820/23 on the galactic plane in the constellation Vulpecula is presented. The stars were chosen from Near Infrared Photographic Sky Survey visual and near-IR photographic pairs and were selected for their visual faintness as well as their red colors. Positions, approximate magnitudes, and finding charts for these stars are presented. It is noted that two members of the list, 1548C858 and 1548C869, have already been determined to be faint, pure S stars.

Observations of the 36.57-day eclipsing binary SX Cas made on eight nights during February and March 1979 with pairs of intermediate- and narrow-band filters centered on the wavelengths of the Balmer H-alpha line and the O I 7774 A triplet are discussed. In addition, a reticon spectrum covering a wavelength range of 4750 A to 7700 A was obtained in September 1979, showing strong H-beta and H-alpha emission lines as well as absorption features of the K-giant component of the system. From the photometry, strong H-alpha emission is found at all the orbital phases sampled. However, no appreciable O I 7774 A line emission is detected. It is noted that the strong H-alpha emission is consistent with the presence of significant amounts of circumstellar and circumbinary gas. From the observations, it appears that the H-alpha emitting region is centered chiefly on the primary component, but the gas is partially eclipsed by the larger cool giant during primary eclipse. The H-alpha-emitting region therefore appears larger than the dimensions of the stellar components. In addition, the apparent nonrepeatability of the H-alpha emission strength from one orbital cycle to the next implies that relatively rapid changes in the extent or quantity of gas occur in the system.

Observation spectroscopique de trois QSO a absorption complexe, de haute ionisation. Les QSO appartiennent a la classe des QSO a raies d'absorption larges et presentent des creux d'absorption a structure considerable (l'absorption n'est pas du type P Cygni classique). On discute de la nature de l'absorption large

Two rich C IV absorption complexes in the radio-loud QSO GC 1556 + 335 are described. Column densities for seven of the redshift systems in these complexes are measured, and limits on the distances between the QSO and absorbing clouds are derived using ionization parameters estimated from matching photoionization models to the observations and a density estimated from an upper limit to the C II(asterisk) column density in the z = 1.65367 redshift system. These limits show that GC 1556 + 335 is not a typical member of the BALQSO class. Two alternative models are discussed in which the absorption complexes are caused by material either entrained into a radio jet from the QSO or contained in two clusters of galaxies along the line of sight. It is suggested that the emission associated with the complexes may be detectable, and that a study of the velocity field and geometry of such emission might be decisive in determining the mechanism responsible for the absorption. 40 references.

The relation between the broad absorption-line region and the broad emission-line region in QSOs is considered. It is demonstrated that the broad absorpiton-line region may give rise to a substantial, high-ionization, broad emission-line component. An inner low-ionization, broad emission-line component must also exist. Future models of the broad emission-line region must incorporate the constraints imposed by the analysis of broad absorption-line region data.