Search Publications

Classical Cepheid Luminosities from Binary Companions

Evans, Nancy Remage

Luminosities for the classical Cepheids Eta Aql, W Sgr, and SU Cas are determined from IUE spectra of their binary companions. Spectral types of the companions are determined from the spectra by comparison with the spectra of standard stars. The absolute magnitude inferred from these spectral types is used to determine the absolute magnitude of th…

Non--LTE Analysis of the Ofpe/WN9 Star HDE 269227 (R84)

Leitherer, Claus; Schmutz, Werner; Hubeny, Ivan +3 more

The paper presents the results of a spectral analysis of the Ofpe/WN9 star HD 269227 (R84), which assumes a spherically expanding atmosphere to find solutions for equations of radiative transfer. The spectra of hydrogen and helium were predicted with a non-LTE model. Six stellar parameters were determined for R84. The shape of the velocity law is …

Discovery of a Fast Radiative Shock Wave in the Cygnus Loop Using the Hopkins Ultraviolet Telescope

Ferguson, Henry C.; Blair, William P.; Gull, Theodore R. +12 more

Observations of the far-ultraviolet spectrum of a bright radiative filament on the eastern edge of the Cygnus Loop supernova remnant are described which were made through the Hopkins Ultraviolet Telescope aboard the Astro-1 Space Shuttle mission in December 1990. Observations include strong emission lines of C III 977, N III 991, and O VI 032, 103…

New Observations of the Gas Cloud Associated with the Quasar-Galaxy Pair 3C 232/NGC 3067

Donahue, Megan; Shull, J. Michael; Stocke, John T. +2 more

We present new optical Na I and Ca II spectra, new Hα images, and archival IUE ultraviolet spectra of the quasar-galaxy pair 3C 232/NGC 3067, to study the H I gas cloud seen in 21 cm emission between the eastern edge of NGC 3067 and 3C 232. High-resolution optical spectra show two, and possibly three, absorption systems in Ca II and Na I, with a l…

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…

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…