Donald E. Osterbrock

Active galactic nuclei

Our current knowledge of active nuclei is reviewed. The importance of observational data taken over a wide range of frequencies, from radio and infrared through optical and ultraviolet to x-rays and y-rays, is emphasized. Important overall principles include the continuity from quasars and QSOs through Seyfert and radio galaxies to low-luminosity LINE-, the importance of considering roughly cylindrically symmetric (rather than spherically symmetric) structures, and that the various regions generally have different axes and planes of symmetry, and are often warped.

Spectral classification of emission-line galaxies

A revised method of classification of narrow-line active galaxies and H II region-like galaxies is proposed. It involves the line ratios which take full advantage of the physical distinction between the two types of objects and minimize the effects of reddening correction and errors in the flux calibration. Large sets of internally consistent data are used, including new, previously unpublished measurements. Predictions of recent photoionization models by power-law spectra and by hot stars are compared with the observations. The classification is based on the observational data interpreted on the basis of these models. 63 references.

Spectra of narrow-line Seyfert 1 galaxies

Measurements are presented of a group of active galactic nuclei with all the properties of Seyfert 1 or 1.5 galaxies, but with unusually narrow H I lines. They include Mrk 42, 359, and 1239 (previously studied by other authors) as well as Mrk 493, 766, 783, and 1126. One other somewhat similar object, Mrk 1388, is also included in the discussion; measurements of its spectrum have been published previously. These narrow-line Seyfert 1 galaxies show a wide variety of deviations from the properties of typical Seyfert 1 objects. They clearly demonstrate that the Seyfert phenomenon is not a simple one-parameter effect. 29 references.

Faint emission lines in the spectrum of the Orion Nebula and the abundances of some of the rarer elements

CCD spectra were obtained of a region just north of the Trapezium in NGC 1976, the Orion Nebula, in overlapping exposures covering the wavelength region λλ3180-11000. Approximately 225 emission lines were measured at a resolution of about 6 A. A total of 35 H I lines and 57 He I lines were identified. Most of their measured intensities, corrected for interstellar extinction, agree relatively well with the recombination-line theory. At the faintest levels there are discrepancies, probably resulting from observational uncertainties

Spectroscopic study of the CfA sample of Seyfert galaxies

High signal-to-noise ratio spectra were obtained of nearly all the Seyfert 2 galaxies in the CfA complete sample published by Huchra & Burg, and of some of the Seyfert 1s as well. Several of the Seyfert 2 galaxies have weak, broad components to their Hα emission lines, and in some cases to Hβ as well, and thus are Seyfert 1.8 or 1.9 objects on the Lick Observatory classification system. Luminosity functions and mean absolute magnitudes were calculated separately for each type and for various groupings of the types. Our spectra confirm Huchra & Burgs conclusion that the CfA sample contains a higher fraction of Seyfert 1s than the Wasilewski sample, which therefore appears to be deficient in faint, reddened Seyfert 1 galaxies

IUE spectra and a resulting model of Seyfert 2 galaxies

Nearly simultaneous optical and ultraviolet observations of several Seyfert 2 galaxies are presented. A mean optical to ultraviolet emission line spectrum for Seyfert 2 galaxies is determined, and these intensities are compared with predictions of photoionization models. The UV to X-ray nonthermal continuum which ionizes this gas is examined. The results suggest that an obscuring layer does not hide an underlying broad-line region, and that narrow-line objects such as Seyfert 2 and narrow-line radio galaxies are physically different from broad-line objects, at least in not having an inner broad-line region. The absence of extinction also distinguishes these classical Seyfert 2 galaxies from the narrow-line X-ray galaxies, which X-ray evidence suggests may be extinguished Seyfert 1 galaxies.

An analysis of the narrow-line profiles in high ionization Seyfert galaxies

Narrow optical emission-line profiles representing a wide range in ionization potential for 12 high-ionization Seyfert galaxies are analyzed using deconvolution techniques. The data reduction process is described in detail. A good correlation is found between line width and ionization potential in many of the objects. For some galaxies a good correlation is also found between line width and critical density. For a given object, the ratios of line widths at various fractions of full intensity are remarkably similar over the entire range of ionization potential and critical density. Almost identical velocity ratios at corresponding fractions of maximum intensity are found for profiles from an individual line (e.g., [Fe vu] ^6087) taken from every object. In particular the relation between the velocity widths at \ and £ maximum intensity is the same found for the widths of the broad profiles of Hß in Seyfert 1 galaxies and QSOs by De Robertis (1984a). This may suggest that a similar acceleration mechanism (and/or geometry) operates in all objects in both the broadand narrow-line regions. The high-ionization line widths correlate only poorly with the absolute blue magnitude of the galaxy, while the lower ionization lines show a good correlation. On average, half of the galaxies have narrow line profiles which are skewed to the blue, half which are symmetric. The low-ionization lines display little asymmetry in general, while the high-ionization lines tend to have blueward excesses. The possible implication of these and other correlations, and the absence of still other correlations, are discussed. Descriptions of the details of the individual spectra are presented. Subject headings: galaxies: Seyfert — line profiles

The nature and structure of active galactic nuclei

Current knowledge of the structure of AGNs and the physical principles that govern them are reviewed, along with clues as to their formation and evolution. Evidence from optical observational data is stressed, but the importance of radio, millimeter, infrared, ultraviolet, and X-ray results is also emphasized. Overall, AGNs form one family, but there are many differences in detail among them. Spectral classification of AGNs is reviewed. Diagnostic diagrams involving optical and near-infrared emission-line ratios to separate AGNs from H II regions or starburst galaxies are briefly discussed. Observed jets indicate that many, if not all, AGNs have an axis, and that cylindrical rather than spherical symmetry governs them

Atoms in Astrophysics

1. Low-Energy Electron Collisions with Complex Atoms and Ions.- 1. Introduction.- 2. Theory of Electron Collisions with Atoms and Ions.- 2.1. Expansion of the Collision Wave Function.- 2.2. Expansion of the Target Wave Function.- 2.3. Variational Principles and the Derivation of the Coupled Integro-Differential Equations.- 2.4. Derivation of the Cross Section.- 2.5. Inclusion of Relativistic Effects.- 2.5.1. Use of the Breit-Pauli Hamiltonian.- 2.5.2. Use of the Dirac Hamiltonian.- 3. Numerical Solution of the Coupled Integro-Differential Equations.- 3.1. Early Work.- 3.1.1. Iterative Methods.- 3.1.2. Reduction to a System of Coupled Differential Equations.- 3.2. Reduction to a System of Linear Algebraic Equations.- 3.3. R-Matrix Method.- 3.4. Matrix Variational Method.- 3.5. Noniterative Integral Equations Method.- 3.6. New Directions.- 3.7. Illustrative Results.- 4. Computer Program Packages.- 4.1. Structure Packages.- 4.2. Collision Packages.- References.- 2. Numerical Methods for Asymptotic Solutions of Scattering Equations.- 1. Introduction.- 2. Specification of Asymptotic Forms.- 3. Travels in Intermedia.- 3.1. Numerical Integration of the Differential Equations.- 3.2. Noniterative Integration of the Phase-Amplitude Equations.- 4. At the Border of Asymptopia.- 4.1. Asymptopic Expansions.- 4.2. Iterative Techniques.- 4.2.1. The Iterated WBK (IWBK) Method.- 4.2.2. The Generalized Matricant.- 5. Concluding Remarks.- References.- 3. Collisions between Charged Particles and Highly Excited Atoms.- 1. Introduction.- 2. The Impact Parameter (IP) Method.- 3. The Sudden Approximation.- 4. Transitions between Levels with Quantum Defects.- 5. Transitions within the Degenerate Sea.- References.- 4. Proton Impact Excitation of Positive Ions.- 1. Introduction.- 2. Excitation of Fine-Structure Transitions.- 2.1. Semiclassical Theory.- 2.2. Quantal Theory.- 3. Excitation of Metastable Transitions.- 4. Charge-Transfer Ionization.- References.- 5. Long-Range Interactions in Atoms and Diatomic Molecules.- 1. Introduction.- 2. General Form of the Model Hamiltonian.- 3. Form of the Model Potential for Atomic Systems.- 3.1. The Exact Interaction between the Valence Electrons and the Core.- 3.2. Second-Order Perturbation Theory: The Static Contribution.- 3.3. The First Nonadiabatic Correction.- 3.4. The Second Nonadiabatic Correction.- 3.5. Nonadiabatic Corrections of Higher Order.- 3.6. Third-Order Perturbation Theory: The Static Contributions.- 3.7. Summary of Results.- 4. Form of the Model Potential for Diatomic Systems.- 4.1. The Exact Interaction between the Valence Electrons and the Cores.- 4.2. Second-Order Perturbation Theory: The Static Contributions.- 4.3. The First Nonadiabatic Correction.- 4.4. The Second Nonadiabatic Correction.- 4.5. Nonadiabatic Corrections of Higher Order.- 4.6. Third-Order Perturbation Theory: The Static Contribution.- 4.7. Summary of Results and the Separated Atom Limit.- 5. Addition Theorems for Solid Harmonics.- References.- 6. Applications of Quantum Defect Theory.- 1. Historical Survey.- 2. Mathematical Background to Quantum Defect Theory.- 2.1. Properties of Coulomb Wave Functions.- 2.2. Solutions of the Coupled Equations.- 2.2.1. All Channels Closed.- 2.2.2. Some Channels Open.- 3. Single-Channel Quantum Defect Methods: General Formulas in the Independent-Particle Approximation.- 3.1. Expressions for the Wave Functions.- 3.2. General Formulas for Radiative Transition Probabilities.- 3.3. Collision Cross Sections.- 3.3.1. Use of Extrapolated Quantum Defects.- 3.3.2. Use of Adjusted Calculated Quantum Defects.- 3.3.3. Use of Observed Quantum Defects in the Bethe Approximation.- 3.4. Summary.- 4. Applications to Simple Multichannel Problems.- 4.1. The Spectrum of Calcium.- 4.1.1. Bound States.- 4.1.2. Autoionizing States.- 4.2. Bound States of Complex Ions by Extrapolation of Calculated Scattering Parameters: Configurations 1s22s22pqnl.- 4.3. The Spectrum of the H2 Molecule.- 5. Extrapolation of the Generalized Reactance Matrix.- 5.1. Discussion of Extrapolation Methods.- 5.1.1. Restrictions on the Validity of Extrapolation Methods.- 5.1.2. Fitting Techniques.- 5.2. Applications.- 5.2.1. Collision Strengths in LS-Coupling.- 5.2.2. Collision Strengths for Excitations between Fine-Structure Levels.- 5.2.3. Photoionization Gross Sections.- 5.2.4. Electron Impact Ionization Cross Sections.- 6. Conclusions.- References.- 7. Electron-Ion Processes in Hot Plasmas.- 1. Introduction.- 2. Line Intensities.- 2.1. Level Populations.- 2.2. Forbidden Lines.- 2.3. Satellite Lines.- 3. Electron-Ion Processes.- 3.1. Introduction.- 3.2. The A+z + e System.- 3.3. Coupling between Open Channels.- 3.4. Resonance Contribution to Collisional Excitation.- 3.5. Approximate Methods for Strong Allowed Transitions.- 3.6. Relativistic Effects.- 3.7. Relativistic Effects in Autoionization.- 4. Conclusion.- A.1. Derivation of am(E) and b?i(E).- A.2. Resonances.- A.3. Gailitis Formula.- References.- 8. The University College Computer Package for the Calculation of Atomic Data: Aspects of Development and Application.- 1. Introduction.- 2. The Growth of Astronomical Observations.- 3. Some Aspects of the Genesis of the Programs.- 4. The C III Challenge.- 4.1. Collision Strengths and Transition Probabilities for the Interpretation of the Solar Spectrum.- 4.2. Excitation of C III by Recombination.- 4.2.1. Observations.- 4.2.2. Rate Coefficients from Detailed Balance Arguments.- 4.2.3. Improved Low-Temperature Coefficients.- References.- 9. Planetary Nebulae.- 1. Introduction.- 2. Observations.- 2.1. Optical.- 2.2. Infrared.- 2.3. Radio.- 2.4. Ultraviolet.- 2.4.1. NGC 7662.- 2.4.2. IC 418.- 2.4.3. The C/O Ratio in Planetary Nebulae.- 3. Models: Atomic Data.- 3.1. Charge Transfer.- 3.1.1. O+.- 3.1.2. O2+.- 3.1.3. Ne2+.- 3.2. Dielectronic Recombination.- 3.3. Photoionization and Radiative Recombination.- 3.4. Electron Collisional Excitation.- 3.5. Radiative Transition Probabilities.- References.- 10. Forbidden Atomic Lines in Auroral Spectra.- 1. Introduction.- 2. Beginnings.- 3. Seatons Work.- 4. Refinement of Classical Theory.- 5. Advent of In Situ Measurements.- 6. N2(A3?u+)-O Excitation Transfer.- 7. Quenching.- 8. Coordinated Rocket and Satellite Measurements.- 9. ?3466 and ?10,400 of N I.- References.

Sky spectra at a light-polluted site and the use of atomic and OH sky emission lines for wavelength calibration

Spectra of the night sky, taken at Lick Observatory in 1988 and 1989 as byproducts of nebular spectra, show the great increase of light pollution by sodium high-pressure and low-pressure lamps in comparison with previous spectra taken in 1975. The usefulness of the emission lines of the night sky spectrum for wavelength calibration is mentioned. In the far red and near-infrared regions, where there are only few atomic night-sky lines, the OH variation-rotation spectrum may be used for this purpose. Accurate rest wavelengths for these lines, calculated from the best laboratory determinations are tabulated, and the special suitability of the P1 (and to a lesser extent P2) lines are discussed.