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Emission from Dust in Visual Reflection Nebulae at Infrared and Submillimeter Wavelengths
Casey, Sean C.
Far-IR and submillimeter images of five bright visual reflection nebulae, IC 446, NGC2247, NGC 2245, NGC 7023, and CED 201 are presented and used with composite IR spectra to derive parameters such as the fraction of nebulae emission attributed to molecule-sized grains, the range of nebulae grain albedos, gas densities, and gas cloud geometries. T…
On the evolutionary link between white dwarfs and central stars of planetary nebulae : NLTE analysis of PG 1144+005.
Werner, K.; Heber, U.
Line-blanketed non-LTE (NLTE) model atmospheres are used to study the optical spectra of the hydrogen-deficient prewhite dwarf PG 1144 + 005 by means of a spectral analysis. The star is compared to a prototype PG 1159 star for the analysis, and the stellar parameters of the PG 1144 dwarf show that the N/O ratio is indicative of very strong nitroge…
Spatially resolved spectroscopy of WR ring nebulae. II. M 1-67.
Smith, L. J.; Esteban, C.; Manchado, A. +1 more
Detailed, high spatial resolution spectroscopy of the WR ring nebula M1-67 surrounding the WN 8 star WR 124 is presented. Abundances for 4 positions in M1-67 are derived and it is found that N is enhanced by a factor of 4 - 7.5, O is deficient by a factor of 5 - 7.5 and S has a normal H II region abundance. This remarkable abundance pattern leads …
Predicted Profiles of Ultraviolet Interstellar Absorption Lines
York, D. G.; Welty, D. E.; Hobbs, L. M.
In this paper, values of the column density, line width parameter, and velocity are determined for as many components derived from optical interstellar absorption-line profiles of Na I and K I as needed to reproduce the observed high-resolution optical profiles of the D lines of Na I toward eight lightly reddened stars and of the 7698 A line of K …
Boundary-layer temperatures in high accretion rate cataclysmic variables.
Drew, Janet E.; Hoare, Melvin G.
The Zanstra method is used to derive limits on boundary-layer temperatures in eclipsing dwarf novae during outburst and nova-like variables, using the observed He II 1640 and 4686 A recombination lines. It is assumed that all the emission is produced in the wind rather than the accretion disk. This method constrains the boundary-layer temperatures…
First Results from the Goddard High-Resolution Spectrograph: Resolved Velocity and Density Structure in the beta Pictoris Circumstellar Gas
Ebbets, Dennis C.; Trafton, L. M.; Boggess, A. +5 more
A Critical Analysis of the Ultraviolet Temperature Scale of the Helium-dominated DB and DBV White Dwarfs
Vennes, Stephane; Shipman, Harry L.; Thejll, Peter
The temperatures of the hottest of the DB and of some of the variable DBV white dwarfs have been reanalyzed, using a new helium-rich model atmosphere grid and archival IUE data. The grid covers variations in the effective temperature, surface gravity, and trace hydrogen abundance. Significantly lower temperatures than those found by earlier invest…
Lyman- alpha Companions to High-z Quasars
Stockton, Alan; Cowie, Lennox L.; Hu, Esther M. +1 more
We report the results of a narrow-band filter search for Lyα companions to z > 2.8 quasars. Three out of 10 radio-loud quasars are found to have candidate Lyα companions, while no candidates are seen in seven optically selected quasars. Follow-up spectroscopy has confirmed two of the candidates, with one yet to be observed. All the companions l…
NGC 1068: Resolution of Nuclear Structure in the Optical Continuum
Faber, S. M.; Seidelmann, P. Kenneth; Currie, Douglas G. +11 more
An optical continuum image of the Seyfert galaxy NGC 1068 has been obtained with the Planetary Camera on the Hubble Space Telescope as part of the SAO/ERO program. The filter used, F547M, has an effective wavelength and a width of approximately 5470 and 650 A and excludes all discrete emission lines that might be present. The point-spread function…
Coordinated X-Ray, Ultraviolet, and Optical Observations of 3C 120
Maraschi, L.; Tanzi, E. G.; Chiappetti, L. +5 more
The results of 14 observations with EXOSAT and 10 quasi-simultaneous observations with IUE of the Seyfert galaxy 3C 120 are reported. On few epochs, quasi-simultaneous optical spectrophotometry was also obtained, allowing us to derive the energy distribution from the optical to the X-ray band in different intensity states. The X-ray spectra are we…