We examine the Lyα absorber population at z < 0.3 detected in spectra of the QSOs PG0953+415 and H1821+643 taken with the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope. We compare their statistical properties to those in carefully-constructed mock quasar spectra drawn from a cosmological hydrodynamic simulation of a ΛCDM universe. We find very good agreement in the colu...

1.1 Dyeing auxiliaries Auxiliaries are compounds which are not an integral part of the dyeing process but by adding them to the dye bath the dyeing can be improved. The main functions of auxiliaries are to prepare or improve the substrate in readiness for colorants (by wetting, providing sorption sites, improving or resisting the migration of dyes), to stabilize the application media (by improv...

Exactly 130 years passed between the discovery by Isaac Newton that white light was composed of colors [1] and the discovery of ultraviolet radiation by Johann Wilhelm Ritter, a German electro chemist, in 1801. We now understand that ultraviolet radiation, although representing <2% of the total number of photons that reach the surface of present-day Earth, has had an important role in the evolu...

Optical/UV observations provide many constraints on accretion disk models of AGN which aren't always appreciated by modelers of the X-ray emission (or sometimes even of the optical/UV emission). The spectral behavior at the Ly edge, the polarization, the continuum slopes and breaks, and the variability timescales and phasing all conflict with simple models and strongly constrain the more Baroqu...

I briefly review the X/UV absorber models and show that the observations of NLS1s are generally consistent with the models. The covering factor of absorbers in NLS1s is likely to be high and there is some evidence of super-solar metallicities. I argue that NLS1s may be active galaxies in the early stage of their evolution and as such, may be low luminosity, low redshift analogues of the high re...

We present a multi–wavelength spectral analysis of the DA white dwarf G 191-B2B. The employed atmospheric models account for gravitational settling and radiative levitation, which are, for the first time, calculated self-consistently with the atmospheric structure. The resulting spectra can reproduce the complete EUVE spectrum and the ultraviolet lines of iron. Some restrictions regarding the U...

Spectra taken with the Space Telescope Imaging Spectrograph (STIS) allow accurate location and extraction of the nuclear spectrum of NGC 4151, with minimal contamination by extended line emission and circumnuclear starlight. Spectra since 1997 show that the P Cygni Balmer and He I absorption seen previously in low nuclear states, is present in higher states, with outflow velocity that changes w...

We explore the effects of UV absorbing material on the shape of the EUV continuum radiation emitted by the active galactic nucleus, and on the relative strengths of emission lines, formed in the narrow line regions of Seyfert galaxies, excited by this continuum. Within a sample of Seyfert 1.5 galaxies, objects with flatter soft X-ray slopes tend to have lower values of He II λ4686/Hβ, which imp...