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Full-Text Articles in Physics

The Chemical Evolution Of Qsos And The Implications For Cosmology And Galaxy Formation, Fred Hamann, Gary J. Ferland Nov 1993

The Chemical Evolution Of Qsos And The Implications For Cosmology And Galaxy Formation, Fred Hamann, Gary J. Ferland

Physics and Astronomy Faculty Publications

We examine the chemical evolution of QSO broad-line gas by applying spectral synthesis and chemical enrichment models to the N V/C IV and N V/He II emission-line ratios. The models indicate that BLR metallicities are typically ~1 to perhaps ≳10 times solar. The enrichment must occur in ≲1 Gyr for sources where the redshift is ≳3 (if q0 = ½). The higher metallicity QSOs require star formation favoring massive stars (compared to the Galactic disk). These results imply that extensive evolution usually occurs before the QSOs become observable. Our models of the evolution are equivalent to models proposed ...


A Masing [Fe Xi] Line, Gary J. Ferland Sep 1993

A Masing [Fe Xi] Line, Gary J. Ferland

Physics and Astronomy Faculty Publications

I draw attention to a maser which occurs within the ground term of Fe10+. In many photoionized environments, infrared fine-structure lines and the [O I] λ6300 line become optically thick but maser amplification of ionic fine-structure lines is unusual. During the course of development of a code designed to simulate gas under radiative-collisional equilibrium, the radiative transfer of roughly 500 ionic/atomic emission lines was treated using escape probabilities. Nearly all forbidden lines can become optically thick under extreme conditions, but the 3Pj = 1, 0 [Fe XI] 6.08 μm transition is the only line which ...


The Dynamics Of Stellar Outflows Dominated By Interaction Of Dust And Radiation, Nathan Netzer, Moshe Elitzur Jun 1993

The Dynamics Of Stellar Outflows Dominated By Interaction Of Dust And Radiation, Nathan Netzer, Moshe Elitzur

Physics and Astronomy Faculty Publications

Wind outflow around a late-type star driven by radiation pressure on dust grains is investigated in detail. The equation of motion for the outflow coupled with the equation of radiative transfer is solved treating the circumstellar envelope, which consists of gas and dust, as a two-component fluid. Because of the drift of the dust particles through the gas, the dust-to-gas ratio varies with distance even if grain formation is a prompt process. The coupling between dust and gas weakens as the mass-loss rate decreases until finally the rate of momentum transfer to the gas is insufficient to overcome gravity when ...


The Narrow-Line Region Of High-Luminosity Active Galactic Nuclei, Beverley J. Wills, H. Netzer, M. S. Brotherton, Mingsheng Han, D. Wills, J. A. Baldwin, Gary J. Ferland, I. W. A. Browne Jun 1993

The Narrow-Line Region Of High-Luminosity Active Galactic Nuclei, Beverley J. Wills, H. Netzer, M. S. Brotherton, Mingsheng Han, D. Wills, J. A. Baldwin, Gary J. Ferland, I. W. A. Browne

Physics and Astronomy Faculty Publications

We have made high signal-to-noise spectroscopic observations of seven radio-loud quasars with the Faint Object Spectrograph on the Hubble Space Telescope and from the ground at McDonald Observatory and at Kitt Peak National Observatory. The resolution is 300-400 km s-1 over the wavelength range 1000-8500 Å, enabling us to separate the broad and narrow components of the emission lines. This is the first study of the optical and UV narrow lines in such high-luminosity active galactic nuclei (AGNs).

The most important and striking observational result is the relative weakness of the narrow ultraviolet lines, assuming that they have the ...