A. Boksenberg

High-resolution spectra of 24 low-redshift QSOs - the properties of Mg II absorption systems

High-resolution spectra of 245 low-redshift QSOs are presented, and Mg II emission-line equivalent widths and velocity widths are measured and briefly discussed. Improved statistical methods are presented for the extraction of significant absorption features from spectra. These techniques provide a simple and accurate estimate of the minimum equivalent widths which could be detected in any region of a spectrum. A search for Galactic Ca II in 13 lines of sight reveals five detections. Equivalent widths are in the range 0.2-0.3 A. Only three redshifted absorption systems were found, all dominated by Mg II 2796 A, 2803 A doublets. Mg(+)/Mg(0) and Mg(+)/Fe(+) values cannot be accounted for by collisional ionization alone. Factors determining the frequency of occurrence of Mg II systems are investigated using a composite sample of 14 systems from the spectra of 90 QSOs. Ten out of the 14 systems occur in five pairs of two systems each per QSO. The probability of these pairs being chance occurrences is only 0.0007. 80 references.

High-resolution study of the absorption spectra of the QSOs Q0002--422 and Q0453--423

High-resolution (0.8 A FWHM) spectroscopic observations over the wavelength range 3800 A--5400 A are presented for the two bright southern QSOs, Q0002--422 (z/sub em/=2.763) and Q0453--423 (z/sub em/=2.656). For these two objects we list 80 and 77 absorption lines, respectively, and identify five absorption-line systems in each object, ranging from z/sub abs/=0.7261 to z/sub abs/=2.4641. All lines longward of L..cap alpha.. emission are successfully identified, but only 18% of those shortward of L..cap alpha.. have yielded to our investigation.A study of the metal-rich absorption systems identified in the two objects here and also in PKS 2126--158 strongly support the notion that the lines originate in galactic halos. The density of systems requires halos of radius approx.30 kpc. The systems at high redshift (z/sub abs/approx.2.5) probably arise from photoionized gas (possibly by the integrated QSO light) and have N (H) approx.10/sup 20/ cm/sup -3/, n (H) approx.0.3 cm/sup -3/, diameter Dapprox.3 x 10/sup 20/ cm, T/sub e/=10/sup 4/ K, and Mapprox.10/sup 3/ M/sub sun/. Roughly 10/sup 6/ objects per galactic halo (of total mass approx.10/sup 9/ M/sub sun/) would be required, so that the clouds do not require a cosmologically significant density, with ..cap omega../sub cloud/=10/sup -3/.

The ultraviolet spectrum of NGC 4151 from 1978 to 1990 : general characteristics and evolution

From the examination of all the low-dispersion IUE spectra of NGC 4151 taken since the launch of IUE in 1978, including the latest data taken in 1990, we follow the evolution of this active nucleus on time scales ranging from days to 10 years. We concentrate our analysis on the campaigns of observations during which the nucleus was not continuously in a minimum state.

PG 0832 + 676 - An apparently normal B1 V star 18 kiloparsecs above the galactic plane

Stellar equivalent widths and line profiles, measured from optical spectra obtained with the 5 m Hale telescope and the 2.5 m Isaac Newton telescope, are used in conjunction with model atmosphere calculations to determine the atmospheric parameters and chemical composition of the faint, blue, high-galactic latitude star PG 0832 + 676. The effective temperature (Teff = 25,000 K), surface gravity (log g = 3.9), and abundances of He, C, N, O, Mg, Al, and Si are similar to those of Population I OB-type stars, from which it is concluded that PG 0832 + 676 is a normal star at a distance from the galactic plane of about 18 kpc. The stars kinematics and evolutionary age suggest that it formed in the halo, possibly from galactic fountain material. 51 refs.

CA-II ABSORPTION-LINES IN THE SPECTRUM OF THE QUASAR PKS 2020-370 DUE TO GALACTIC MATERIAL IN THE GROUP KLEMOLA-31

In the spectrum of the quasar PKs 2020--370 (z/sub em/ = 1.050), we find Ca II absorption lines both at near zero redshift and at z/sub abs/ = 0.02865 +- 0.00007. The latter is closely similar to the redshifts of two galaxies in the group Klemola 31, which are nearby on the plane of the sky. This observation adds to the evidence that the narrow-lined heavy-element absorption systems in quasar spectra in general arise in the extended halos of intervening galaxies.

Interstellar magnesium absorption in the direction of four unreddened stars

Spectral observations of the interstellar lines of Mg

The Lyman limit absorption system in the spectrum of PKS 2126-158 - Heavy-element abundance at high redshift

sup +

Simultaneous EXOSAT-IUE observations of NGC 4151

at 2795 and 2802 A and Mg

Ultraviolet, Optical and X-Ray Monitoring of the Continuum of NGC 4151

sup 0

Velocity dispersions for 13 galaxies.

at 2852 A have been made with a resolution of 0.1 A, toward several stars, with an objective grating spectrograph mounted on a balloon-borne, star-stabilized platform. The analysis of the spectra of four, nearby, unreddened stars is discussed, and values for the interstellar Mg abundance and electron density for the gas in these directions are derived. (AIP)