view Abstract Citations (33) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Effects of Ionizing Radiation Pressure in Quasars and X-Ray Sources Tarter, C. Bruce ; McKee, Christopher F. Abstract Self-consistent calculations of the radiative accelcration in gases excited by power-law, bremsstrahlung, and hlackhcdy ionizing sources are presented. The acceleration can he orders of magnitude greater than that due to Thomson scattering, which effectively reduces the Eddington limiting luminosity. The results are applied to current theoretical models for cosmic X-ray sources and for the line-producing regions of quasars. Subject headings: quasi-stellar sources or objects - X-ray sources Publication: The Astrophysical Journal Pub Date: December 1973 DOI: 10.1086/181358 Bibcode: 1973ApJ...186L..63T full text sources ADS |
view Abstract Citations (668) References (61) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Two-phase models of quasar emission line regions. Krolik, J. H. ; McKee, C. F. ; Tarter, C. B. Abstract It is demonstrated that the emitting gas in clouds of quasar emission line regions must be confined by a hot intercloud medium, provided only that the heating mechanisms are strong enough to drive the low-density intercloud gas above a few tens of millions degrees K. The study of the thermal properties of the gas presented includes heating by photoionization, Compton scattering, suprathermal particles, absorption of radio frequency radiation, cloud friction, thermal conduction, and shocks. Cooling curves for photoionized gases are presented, and phase diagrams analogous to the pressure-temperature diagrams used in studying the interstellar medium are constructed for various conditions. It is shown that two-phase equilibria occur over a wide range of mean density, but over a much narrower range of pressure. The implications of these results for the emission line region are discussed, and it is shown that the emission clouds may be short-lived. Publication: The Astrophysical Journal Pub Date: October 1981 DOI: 10.1086/159303 Bibcode: 1981ApJ...249..422K Keywords: Astronomical Models; Emission Spectra; Hydrogen Clouds; Quasars; Two Phase Flow; X Ray Sources; Compton Effect; Gas Temperature; Line Spectra; Phase Diagrams; Photoionization; Spectrum Analysis; Astrophysics full text sources ADS |
view Abstract Citations (60) References (44) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Radiation pressure in quasar clouds. McKee, C. F. ; Tarter, C. B. Abstract Thee effects of ionizing radiation pressure on optically thick clouds are analyzed, and the results applied to quasars. The analysis shows that the radiative acceleration of a cloud is at least 10 percent of the fully optically-thin value unless the continuum optical depth is very large. The acceleration produced by line absorption is confined to the face of the cloud which is exposed to the incident flux, while the acceleration due to the continuum radiation increases inside the cloud. The disruptive effect of internally created line photons is analyzed for the case of an optically thick continuum, and it is found that the disruptive acceleration can be greatly enhanced and that it is anisotropic, tending to blow off the back side of the cloud. It is concluded that if quasar clouds are radiatively accelerated, they are optically thin. This result is shown to be consistent with observations. Confinement of the clouds is discussed, and it is shown that photoionized clouds cannot be confined by radiation pressure alone. A model for absorption lines produced by numerous small clouds is developed, and it is argued that the absorption lines most likely arise outside the emission-line region. Publication: The Astrophysical Journal Pub Date: December 1975 DOI: 10.1086/153978 Bibcode: 1975ApJ...202..306M Keywords: Hydrogen Clouds; Quasars; Radiation Pressure; Radiative Transfer; Absorption Spectra; Electromagnetic Absorption; Line Spectra; Mathematical Models; Optical Thickness; Photoionization; Astrophysics full text sources ADS |
Very brief summaries of work at LLL related to astronomy are given. The work can be divided into three categories: computational modeling of astrophysical systems, high-altitude observations, and theoretical and experimental determination of atomic and nuclear properties. Research was conducted in the following areas: planetary and stellar evolution, supernovae and nucleosynthesis, nebulae and the interstellar medium, observational x-ray astronomy, theoretical high-energy astrophysics, and related research on equations of state of evolving low-mass stars and giant planets, opacities and plasma spectroscopy, and a theory of two-body reaction rates in a relativistic plasma. (RWR)
view Abstract Citations (17) References (11) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Implications of the Copernicus Observations of Unreddened Stars Weisheit, Jon C. ; Tarter, C. Bruce Abstract A variety of simple models for the absorbing gas between X Sco and the Earth are analyzed in order to interpret the OAO observations of interstellar absorption lines. Our calculations show that the data cannot be reconciled with either the cosmic-ray or X-ray steady-state ionization models of the interstellar medium, and that material in an H u/H I region surrounding X Sco probably provides the dominant contribution to the lines. Subject headings: cosmic rays - interstellar matter - X-rays Publication: The Astrophysical Journal Pub Date: November 1973 DOI: 10.1086/181351 Bibcode: 1973ApJ...186L..33W full text sources ADS | data products SIMBAD (4) Related Materials (1) Erratum: 1974ApJ...188L..77W
Research on astrophysics is summarized including planetary and stellar structure, supernovae and nucleosynthesis, nebulae and the interstellar medium, and high energy astrophysics. Also described are equations of state and opacities and plasma spectroscopy. (JFP)
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