Lyman Spectra Research Articles

Optically thick lines in a quiescent prominence - Profiles of Lyman-alpha, Lyman-beta /H I/, K and H /Mg II/, and K and H /Ca II/ lines with the OSO 8 LPSP instrument

view Abstract Citations (56) References (40) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Optically thick lines in a quiescent prominence - Profiles of Lyman-alpha, Lyman-beta /H I/, K and H /Mg II/, and K and H /Ca II/ lines with the OSO 8 LPSP instrument Vial, J. C. Abstract The first set of simultaneous measurements are presented of H I Lyman-alpha and Lyman-beta, Ca II K and H, and Mg II k and h lines in a quiescent prominence. It is found that: (1) Ca II resonance lines have low opacity, with an optical thickness at the center of the K line varying between 1.4 and 3.2, and nonthermal velocities ranging from 5 to 9 km/sec.; (2) the resonance lines of Mg II, as measured in the whole prominence, depart from Gaussian profiles and are unexplainably broader than the corresponding Ca II ones. The observed Mg II and Ca II 'inverted' intensity ratios may be due to different incident intensities ratios; and (3) the Lyman-alpha and Lyman-beta lines of H I have the same reversals as the chromospheric lines in bright regions, and unreversed profiles may be observed in darker regions. The intensities are larger than the diluted incident radiation, and the opacity reaches values of 100,000. Publication: The Astrophysical Journal Pub Date: February 1982 DOI: 10.1086/159639 Bibcode: 1982ApJ...253..330V Keywords: Line Spectra; Optical Thickness; Solar Prominences; Solar Spectra; Solar X-Rays; Calcium Isotopes; H Lines; Hydrogen Isotopes; K Lines; Lyman Spectra; Magnesium Isotopes; Spectroheliographs; Solar Physics full text sources ADS |

The formation of emission lines in quasars and Seyfert nuclei

view Abstract Citations (549) References (83) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The formation of emission lines in quasars and Seyfert nuclei Kwan, J. ; Krolik, J. H. Abstract The photoionization and heating throughout a quasar emission-line cloud optically thick at the Lyman edge are calculated. Photoionization and collisional ionization from excited states of hydrogen are included, which maintain a substantial electron fraction after the exhaustion of Lyman continuum photons halts ground-state photoionization. Observed values are explained for Ly-alpha/H-beta, H-alpha/H-beta, P-alpha/H-alpha, He I 5876/H-beta, O I 8446/H-alpha, and Mg II 2798/H-beta. The dependence of line strengths on physical conditions is discussed, and plotting Fe II/4570/H-beta versus Balmer continuum/H-beta is suggested. Other observations are also suggested, and the degree of asymmetry is given between the forward and backward emission of lines from a finite slab to make possible the use of comparative line profile studies to elucidate cloud kinematics. Publication: The Astrophysical Journal Pub Date: November 1981 DOI: 10.1086/159395 Bibcode: 1981ApJ...250..478K Keywords: Astronomical Models; Emission Spectra; Galactic Nuclei; Line Spectra; Quasars; Seyfert Galaxies; Balmer Series; Ionic Collisions; Iron; Lyman Spectra; Metal Ions; Optical Thickness; Photoionization; Plasma Heating; Spectral Energy Distribution; Astrophysics full text sources ADS |

Two contrasting Abell planetary nebulae

view Abstract Citations (8) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Two constrasting Abell planetary nebulae. Kaler, J. B. ; Hartkopf, W. I. Abstract The paper presents line fluxes, radial velocities, and analyses of two large Abell-type planetaries that show marked contrasts. Abell 43 is a high-excitation galactic-disk, or Population I, nebula that is optically thin in the hydrogen Lyman continuum. Abell 50 is a medium-excitation, optically thick, Population II (high velocity) object. Although the two nebulae are of similar size (radius greater than 0.2 pc), which in a simple theory might imply a similar evolutionary state, the central star of A43 appears to be much more luminous than that of A50. The set of large nebulae does not constitute a homogeneous evolutionary class in which the stars can be linked by a monotonic evolutionary track. The comparisons between these two objects illustrate and perhaps epitomize very large differences among large planetaries which probably involve differences in population type, and in stellar and nebular masses. Publication: The Astrophysical Journal Pub Date: October 1981 DOI: 10.1086/159320 Bibcode: 1981ApJ...249..602K Keywords: Planetary Nebulae; Radial Velocity; Star Distribution; Stellar Evolution; Abundance; Data Reduction; Disk Galaxies; H Lines; Lyman Spectra; Optical Thickness; Stellar Mass; Astrophysics full text sources ADS | data products SIMBAD (2)

Detection of Lyman continuum absorption in the BL Lacertae object PKS 0735+178

view Abstract Citations (15) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Detection of Lyman continuum absorption in the BL Lacertae object PKS0735+178. Bregman, J. N. ; Glassgold, A. E. ; Huggins, P. J. Abstract The detection of the Lyman edge in the BL Lac object PKS 0735+178 at the absorption red shift determined by optical measurements leads to a lower limit for the column density of atomic hydrogen, N(H I) not less than 4(17)/sq cm. The Lyman-alpha absorption line appears to have been detected, but only an approximate upper limit can be obtained from the data, of the order of 2(19)/sq cm. This amount of atomic hydrogen is less than that for a line of sight through the disk of a normal spiral galaxy. It is suggested that the absorbing material exists either in the halo of a galaxy or in the tenuous, extended, gaseous disk of a galaxy. Publication: The Astrophysical Journal Pub Date: October 1981 DOI: 10.1086/159253 Bibcode: 1981ApJ...249...13B Keywords: Bl Lacertae Objects; Lyman Spectra; Quasars; Ultraviolet Absorption; Absorption Spectra; Gas Density; Hydrogen Atoms; Iue; Red Shift; Astronomy full text sources ADS | data products SIMBAD (1) NED (1) MAST (1)

H2 fluorescence and the diffuse galactic light in the vacuum ultraviolet

view Abstract Citations (34) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS H2 fluorescence and the diffuse galactic light in the vacuum ultraviolet Duley, W. W. ; Williams, D. A. Abstract Fluorescence by molecular H2 within the Lyman and Werner bands, as well as to continuum levels of the X 1 Sigma g + state, occurs at wavelengths less than or equal to 0.18 micron. This emission is shown to be of intensity comparable to that scattered by dust over the same wavelength range in diffuse clouds. The implied increase in dust albedo in the vacuum ultraviolet is likely due to this effect. Thus the small particles responsible for VUV extinction are of conventional chemical composition, i.e., absorbing oxides, silicates, or carbons. Publication: The Astrophysical Journal Pub Date: December 1980 DOI: 10.1086/183427 Bibcode: 1980ApJ...242L.179D Keywords: Diffuse Radiation; Far Ultraviolet Radiation; Fluorescence; Galactic Radiation; Hydrogen; Interstellar Gas; Interstellar Matter; Astrophysics; Extinction; Lyman Spectra; Astrophysics full text sources ADS |

The distribution of Lyman-alpha absorption lines in the spectra of six QSOs - Evidence for an intergalactic origin

view Abstract Citations (589) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The distribution of Lyman-alpha absorption lines in the spectra of six QSOs: evidence for an intergalactic origin. Sargent, W. L. W. ; Young, P. J. ; Boksenberg, A. ; Tytler, D. Abstract The large Lyman-alpha samples in five QSOs with zem between 2.2 and 3.3 are used to test whether the absorbing gas is cosmologically distributed or ejected from the QSOs. It is shown that there is no significant variation in line density with redshift, nor in the rest equivalent width spectrum among the QSOs. In addition, the mean number density of lines in each object is found to be the same, that is, 60 lines per delta z=1 with W greater than or equal to 0.32 A. Publication: The Astrophysical Journal Supplement Series Pub Date: January 1980 DOI: 10.1086/190644 Bibcode: 1980ApJS...42...41S Keywords: Absorption Spectra; Galactic Evolution; Intergalactic Media; Lyman Spectra; Quasars; Astronomical Coordinates; Cosmology; Line Spectra; Red Shift; Tables (Data); Astrophysics full text sources ADS | data products NED (15) SIMBAD (6)

The emission-line spectrum of 3C 48

view Abstract Citations (14) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The emission-line spectrum of 3C 48. Thuan, T. X. ; Oke, J. B. ; Bergeron, J. Abstract The spectrum and absolute energy distribution of the quasar 3C 48 are analyzed, yielding the following results. The forbidden lines are blueshifted with respect to the permitted lines by 600 km/s. The Balmer lines can be decomposed into a narrow and a broad component, with the narrow component having the redshift of the forbidden lines. The Mg II profile fits well the broad components of H-beta and H-gamma along with the Fe II profiles, and the forbidden O II profile fits well the profiles of forbidden O III and higher-ionization forbidden lines. The spatial coverage in the broad-line region is large, ranging from 0.1 to 0.4, and the optical depth at the Lyman limit is much greater than unity; the electron density is greater than 10 million per cu cm. The forbidden-line region has a lower density (less than 1 million per cu cm) and is subdivided into a low-excitation (forbidden O II) and high-excitation (forbidden O III) zone. The helium abundance appears to be normal. Publication: The Astrophysical Journal Pub Date: June 1979 DOI: 10.1086/157090 Bibcode: 1979ApJ...230..340T Keywords: Astronomical Spectroscopy; Emission Spectra; Forbidden Transitions; Frequency Shift; Line Spectra; Quasars; Balmer Series; H Beta Line; H Gamma Line; Iron; Lyman Spectra; Magnesium; Oxygen; Astrophysics; Emission Lines:Quasars full text sources ADS | data products SIMBAD (1) NED (1)

Ultraviolet pumping of N/+/ fine-structure levels

view Abstract Citations (12) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Ultraviolet pumping of N+ fine-structure levels. Flannery, B. P. ; Rybicki, G. B. ; Sarazin, C. L. Abstract The effects of radiative pumping, through the six-line UV 3D - 3P multiplet at 1085 A, on the population of the fine-structure levels of N(+) are investigated. Results are presented for both optically thin and optically thick media. For the more important case of an optically thick nebula, an efficient method is outlined for the numerical solution of the multiline multilevel radiative-transfer problem in a model H II region described by plane-parallel geometry, point source illumination, and homogeneous physical conditions. The method is applied to construct a grid of models for N(+) spanning a wide range of values for the electron density, the strength of the UV source, and the line optical depth of the nebula. In general it is found that radiative pumping and transfer effects can significantly alter the level populations, but the effect often mimics results obtained without radiative pumping with a different electron density. For Stroemgren spheres around early-type stars it is found as a result of transfer effects, the role of pumping is never likely to be important. Infrared emission from the fine-structure decays at 122 and 240 microns is also discussed. Publication: The Astrophysical Journal Pub Date: May 1979 DOI: 10.1086/157040 Bibcode: 1979ApJ...229.1057F Keywords: Fine Structure; Nebulae; Nitrogen Ions; Optical Pumping; Ultraviolet Astronomy; Atomic Excitations; Doppler Effect; Electron Density (Concentration); Energy Levels; H Ii Regions; Lyman Spectra; Radiative Transfer; Statistical Distributions; Stellar Evolution; Stellar Spectra; Astrophysics; H II Regions:Radiative Transfer; Line Formation full text sources ADS |

Implications of high-velocity interstellar H I absorption features

view Abstract Citations (19) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Implications of high-velocity interstellar H I absorption features. Cowie, L. L. ; Laurent, C. ; Vidal-Madjar, A. ; York, D. G. Abstract Contributions to the interstellar H I column density at high velocities from immediate postshock gas and from the cooling gas behind a shock are compared. The detection of high-velocity H I in L-epsilon and L-delta for Iota Ori is reported and interpreted as cooling gas behind a shock of 100 km/s velocity. The immediate postshock gas should be observable for shock velocities greater than 200 km/s and permits direct determination of the velocities of adiabatic shocks in the interstellar medium. It is pointed out that interstellar L-alpha and L-beta lines may not have purely Lorentzian profiles if high-velocity H I is a widespread phenomenon. Publication: The Astrophysical Journal Pub Date: April 1979 DOI: 10.1086/182934 Bibcode: 1979ApJ...229L..81C Keywords: Absorption Spectra; Hydrogen Clouds; Interstellar Gas; Shock Wave Propagation; Adiabatic Conditions; Gas Density; Lyman Spectra; Propagation Velocity; Astrophysics; Interstellar Lines; Interstellar Matter:Neutral Hydrogen; Interstellar Matter:Shock Waves full text sources ADS |

The L-alpha/H-beta/P-alpha ratio in the quasar PG 0026+129

view Abstract Citations (18) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Lalpha /Hbeta /Palpha ratio in the quasar PG 0026+129. Baldwin, J. A. ; Rees, M. J. ; Longair, M. S. ; Perryman, M. A. C. Abstract Observations of the quasar PG 0026+129 with the International Ultraviolet Explorer have determined its L-alpha intensity. In conjunction with visual and infrared observations by Puetter et al. (1978), a L-alpha/H-beta/P-alpha ratio of 6:1:1.4 is derived. The ratios differ from those found in 3C 273. The implications of these observations are discussed. Publication: The Astrophysical Journal Pub Date: December 1978 DOI: 10.1086/182830 Bibcode: 1978ApJ...226L..57B Keywords: H Lines; Line Spectra; Quasars; Ultraviolet Astronomy; H Beta Line; Lyman Spectra; Paschen Series; Satellite-Borne Instruments; Astrophysics; Line Formation:Quasars; Lyman Alpha:Quasars full text sources ADS | data products SIMBAD (2) NED (2) MAST (1) INES (1)

Sequential formation of subgroups in OB associations

view Abstract Citations (1208) References (63) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Sequential formation of subgroups in OB associations. Elmegreen, B. G. ; Lada, C. J. Abstract We reconsider the structure and formation of OB associations in view of recent radio and infrared observations of the adjacent molecular clouds. As a result of this reexamination, we propose that OB subgroups are formed in a step-by-step process which involves the propagation of ionization (I) and shock (S) fronts through a molecular cloud complex. OB stars formed at the edge of a molecular cloud drive these I-S fronts into the cloud. A layer of dense neutral material accumulates between the I and S fronts and eventually becomes gravitationally unstable. This process is analyzed in detail. Several arguments concerning the temperature and mass of this layer suggest that a new OB subgroup will form. After approximately one-half million years, these stars will emerge from and disrupt the star-forming layer. A new shock will be driven into the remaining molecular cloud and will initiate another cycle of star formation Several observed properties of the OB associations are shown to follow from such a sequential star-forming mechanism. These include the spatial separation and systematic differences in age of OB subgroups in a given association, the regularity of the subgroup masses, the alignment of subgroups along the galactic plane, and their physical expansion. Detailed observations of ionization fronts, masers. IR sources, and molecular clouds are also in agreement with this model. Finally, this mechanism (e.g., T. Tauri stars) which may have formed ahead of the shock as part of the original cloud collapsed and fragmented. Publication: The Astrophysical Journal Pub Date: June 1977 DOI: 10.1086/155302 Bibcode: 1977ApJ...214..725E Keywords: B Stars; Lyman Spectra; Nebulae; O Stars; Star Clusters; Stellar Evolution; Interstellar Gas; Protostars; Shock Fronts; Stellar Models; Stellar Structure; Astrophysics full text sources ADS | data products SIMBAD (10)

The nature of the nebulosity around 3C 48

view Abstract Citations (21) References (11) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The nature of the nebulosity around 3C 48. Bergeron, J. Abstract An attempt is made to show that the observed emission-line spectrum of the nebulosity on the north side of quasar 3C 48 is consistent with a model spectrum arising from the excitation of an extended H I disk by a quasar event in a galactic nucleus. The mass and column density of the nebulosity are estimated, and it is found that if a cosmological distance is assumed, the nebulosity is similar in dimensions, mass, and column density to the extended H I disks around nearby spiral galaxies. Possible heating sources for the nebulosity are investigated, the heavy-element abundance is determined as a function of heating source, and the continuous radiative emission from the quasar is evaluated as an energy source for the nebulosity. Based on the results, the nebulosity is modeled as an 'extended galactic disk' moderately ionized by the high-energy tail of the quasar's continuum. The possible degree of clumpiness or flatness of the nebulosity is also determined. Publication: The Astrophysical Journal Pub Date: December 1976 DOI: 10.1086/154830 Bibcode: 1976ApJ...210..287B Keywords: Abundance; Emission Spectra; Hydrogen Clouds; Line Spectra; Nebulae; Quasars; Astronomical Models; Galactic Nuclei; Gas Ionization; H Alpha Line; Heavy Elements; Lyman Spectra; Optical Density; Radiant Flux Density; Radiative Heat Transfer; Spiral Galaxies; Astrophysics full text sources ADS | data products NED (1)

Lyman-alpha observations of Comet Kohoutek 1973 XII with Copernicus

view Abstract Citations (26) References (24) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Lyman-alpha observations of comet Kohoutek 1973 XII with Copernicus. Drake, J. F. ; Jenkins, E. B. ; Bertaux, J. L. ; Festou, M. ; Keller, H. U. Abstract Comet Kohoutek 1973 XII was observed with a telescope-spectrometer on the Copernicus satellite on six occasions over a 1-month period starting on January 29, 1974. Positive detection of the cometary Ly-alpha emission profile was obtained on January 29 and February 2. Earlier observations of the geocoronal Ly-alpha emission profile allowed an instrumental intensity calibration and confirmation of the computed instrumental profile for an extended source at the Ly-alpha wavelength. After allowing for broadening by the instrument, a hydrogen-outflow velocity of about 10.6 km/s is derived from the width of the Ly-alpha emission on January 29. The intensity calibration combined with an appropriate cometary model led to cometary water-production rates for January 29 and February 2. Only upper limits were obtained for Ly-alpha on and after February 14. Searches for OH and D led to negative results. Publication: The Astrophysical Journal Pub Date: October 1976 DOI: 10.1086/154721 Bibcode: 1976ApJ...209..302D Keywords: Astronomical Spectroscopy; Calibrating; Kohoutek Comet; Lyman Alpha Radiation; Lyman Spectra; Oao 3; Emission Spectra; Satellite Observation; Spaceborne Astronomy; Telescopes; Astronomy full text sources ADS |

Radiative shock dynamics. I - The Lyman continuum

view Abstract Citations (35) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Radiative shock dynamics. I. The Lyman continuum. Klein, R. I. ; Stein, R. F. ; Kalkofen, W. Abstract The paper investigates coupled non-LTE radiative transfer and nonlinear hydrodynamics by considering a shock propagating outward through an atmosphere of pure hydrogen in which the hydrogen atoms have one bound level and a continuum. Self-consistent numerical solutions are obtained for the nonlinear hydrodynamic equations, the transfer equation for Lyman continuum radiation, and the time-dependent population equation for atoms with one bound level plus continuum. Results are discussed for a piston-driven shock propagating through a static atmosphere in radiative and statistical equilibrium, with attention given to the formation of the ionization front, the ionization contour, and the radiation intensity at the Lyman edge. The structure of the temperature spike developed by the shock is compared for the three cases of adiabatic, collisional, and radiating shocks. It is shown that the escape of recombination radiation narrows the temperature spike at small optical depth and that low postshock densities in the upper atmosphere reduce the three-body recombination rate and produce a large plateau of nearly constant ionization behind the shock. Publication: The Astrophysical Journal Pub Date: April 1976 DOI: 10.1086/154304 Bibcode: 1976ApJ...205..499K Keywords: Hydrodynamics; Hydrogen Atoms; Lyman Spectra; Radiative Transfer; Shock Wave Propagation; Stellar Atmospheres; Atmospheric Models; Continuous Radiation; Finite Difference Theory; Gas Ionization; Hydrodynamic Equations; Temperature Profiles; Thermodynamic Equilibrium; Astrophysics full text sources ADS |

Ultraviolet observations of cool stars. IV - Intensities of Lyman-alpha and MG II in epsilon Pegasi and epsilon Eridani, and line width-luminosity correlations

view Abstract Citations (52) References (24) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Ultraviolet observations of cool stars. IV. Intensities of Lyman-alpha and Mg II in Epsilon Pegasi and Epsilon Eridani, and line width-luminosity correlations. McClintock, W. ; Henry, R. C. ; Moos, H. W. ; Linsky, J. L. Abstract A spectrometer on the Copernicus satellite has been used to confirm the existence of a line width-luminosity relation for the Ly-alpha and Mg II 2800-A chromospheric emission lines in K-type stars by observation of a K2 dwarf (epsilon Eri) and a K2 supergiant (epsilon Peg). Combined with previously reported observations of lines in three K giants (alpha Boo, alpha Tau, and beta Gem), the data are consistent with an identical dependence of line width on absolute visual magnitude for the Ca II K, Ly-alpha, and Mg II 2795-A lines. Surface fluxes of Ly-alpha, Mg II 2800-A, and O V 1218-A (upper limit) for epsilon Eri, and of Mg II 2800-A for epsilon Peg are also compared with values reported previously for the three giant stars. Publication: The Astrophysical Journal Pub Date: December 1975 DOI: 10.1086/154026 Bibcode: 1975ApJ...202..733M Keywords: Cool Stars; Emission Spectra; K Stars; Late Stars; Line Spectra; Stellar Evolution; Ultraviolet Spectra; Atmospheric Radiation; Calcium; Chromosphere; Giant Stars; Lyman Spectra; Radiant Flux Density; Spectral Line Width; Stellar Luminosity; Stellar Spectra; Astrophysics full text sources ADS | data products SIMBAD (5) Related Materials (7) Part 1: 1974ApJ...188L..93M Part 2: 1974ApJ...193L.107G Part 3: 1975ApJ...202..165M Part 5: 1976ApJ...204L.103M Part 6: 1978ApJS...37..223M Part 7: 1978ApJ...225..465M Part 8: 1978ApJ...226..883A

Interstellar clouds containing optically thick H2

view Abstract Citations (186) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Interstellar clouds containing optically thick H2. Jura, M. Abstract Interstellar clouds containing optically thick H2 are investigated on the basis of the hypothesis that the population of the H2 rotational levels can be understood in terms of optical pumping in the Lyman and Werner bands. The observed populations are used to infer the densities and radiation fields within the clouds. The theoretical model adopted for an interstellar cloud and the analytical procedure are described. It is found that, of the 10 clouds studied, five are illuminated by a UV field appropriate to within a factor of two to that in the solar neighborhood, four appear to be near the stars against which they are observed, and one is irradiated by a very low intensity field. The results suggest that there are substantial pressure variations in the interstellar gas, even among those clouds not located near H II regions. Publication: The Astrophysical Journal Pub Date: May 1975 DOI: 10.1086/153546 Bibcode: 1975ApJ...197..581J Keywords: Interstellar Matter; Molecular Spectra; Optical Thickness; Astronomical Models; Cosmic Dust; H Ii Regions; Hydrogen Ions; Lyman Spectra; Mathematical Models; Molecular Rotation; Optical Pumping; Population Theory; Pressure Distribution; Ultraviolet Radiation; Astrophysics full text sources ADS | data products SIMBAD (11)

Interstellar absorption lines in the spectrum of zeta Ophiuchi

view Abstract Citations (639) References (104) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Interstellar absorption lines in the spectrum of Zeta Ophiuchi. Morton, D. C. Abstract Extensive high-resolution scans with the Copernicus UV spectrometer are combined with available ground-based data on interstellar lines to obtain temperatures, densities, and abundances in H I clouds and H II regions in the direction of zeta Oph. Column densities are obtained for 21 elements in various ionization stages, and upper limits are reported for 5 elements and 11 molecules. Analysis of radial velocities and growth curves indicates that H2, HD, and most neutral atoms are concentrated in one cloud with a heliocentric velocity of -14.4 km/s and that H II regions exist in addition to the Stroemgren sphere. The electron and proton densities are calculated for the -14.4 km/s cloud, and the temperatures required for the populations of the fine-structure levels in the C I ground state and the excited rotational levels of H2 are computed and indicate that the dense cloud must have some associated hotter regions. Relative to hydrogen, most of the elements in the H I clouds are found to be depleted by factors of 3 to 4000 as compared with solar system abundances, and several elements appear to be depleted in the H II regions as well. Publication: The Astrophysical Journal Pub Date: April 1975 DOI: 10.1086/153490 Bibcode: 1975ApJ...197...85M Keywords: Absorption Spectra; Astronomical Spectroscopy; Interstellar Extinction; Line Spectra; Ultraviolet Spectra; Abundance; Far Ultraviolet Radiation; Fine Structure; H Ii Regions; Hydrogen Atoms; Hydrogen Ions; Lyman Spectra; Neutral Particles; Radial Velocity; Tables (Data); Astrophysics full text sources ADS | data products SIMBAD (1)

Starlight excitation of permitted lines in the Orion Nebula

view Abstract Citations (93) References (19) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Starlight excitation of permitted lines in the Orion nebula. Grandi, S. A. Abstract From an idealized model of the Orion Nebula and from an analysis of line ratios it is shown that direct starlight excitation of the permitted O I lines dominates over recombination and Lyman-line fluorescence. The line strengths predicted by this mechanism agree reasonably well with those observed in the Orion Nebula. The application of direct starlight excitation to other ions is also discussed. Publication: The Astrophysical Journal Pub Date: March 1975 DOI: 10.1086/153426 Bibcode: 1975ApJ...196..465G Keywords: Astronomical Models; Line Spectra; Oxygen Spectra; Planetary Nebulae; Electron Transitions; Fluorescence; Gas Ionization; Lyman Spectra; Recombination Reactions; Spectral Line Width; Astrophysics full text sources ADS | data products SIMBAD (2)