Search Publications
Detection of intergalactic ionized helium absorption in a high-redshift quasar
Boksenberg, A.; Deharveng, J. M.; Jakobsen, P. +3 more
Observations obtained with the recently refurbished Hubble Space Telescope reveal strong absorption arising from singly ionized helium along the line of sight to a high-redshift quasar. The strength of the absorption suggests that it may arise in a diffuse ionized intergalactic medium. The detection also confirms that substantial amounts of helium…
Hubble Space Telescope Photometry of the Central Regions of Virgo Cluster Elliptical Galaxies. III. Brightness Profiles
Jaffe, W.; Ford, H. C.; O'Connell, R. W. +2 more
We have used the Planetary Camera on the Hubble Space Telescope to study the morphology and surface brightness parameters of a luminosity-limited sample of fourteen elliptical galaxies in the Virgo cluster. The total apparent blue magnitudes of the galaxies range between 9.4 and 13.4. In this paper, the core brightness profiles are presented, whil…
The Morphology of Distant Cluster Galaxies. I. HST Observations of CL 0939+4713
Dressler, Alan; Oemler, Augustus, Jr.; Butcher, Harvey R. +1 more
We have obtained Hubble Space Telescope (HST) WFC observations of CL 0939+4713, a very rich cluster at z = 0.41 which exhibits an excess population of blue galaxies typical of clusters at that redshift. The images are of sufficient quality, despite the HST spherical aberration problems, to permit assignment of Hubble types to galaxies brighter tha…
Acceleration of interstellar pickup ions in the disturbed solar wind observed on Ulysses
Geiss, J.; Lanzerotti, L. J.; Roelof, E. C. +6 more
Acceleration of interstellar pickup H+ and He+ as well as of solar wind protons and alpha particles has been observed on Ulysses during the passage of a corotating interaction region (CIR) at ~4.5 AU. Injection efficiencies for both the high thermal speed interstellar pickup ions (H+ and He+) and the low…
An IUE Survey of Interstellar H i Lyman-Alpha Absorption. II. Interpretations
Savage, Blair D.; Diplas, Athanassios
We present an analysis of interstellar neutral hydrogen column densities obtained from archival Ly alpha absorption line data toward the complete sample of B2 and hotter stars observed at high spectral resolution with the IUE satellite. The full sample includes 554 stars and more than doubles the number of lines of sight previously observed. Many …
Radiation-driven winds of hot luminous stars. XII. A first step towards detailed UV-line diagnostics of O-stars.
Butler, K.; Kudritzki, R. P.; Pauldrach, A. W. A. +2 more
Improved radiation driven wind models are constructed to calculate detailed synthetic UV spectra of hot luminous stars. The model improvements comprise: a very detailed multilevel non-local thermodynamic equilibrium (NLTE) treatment of 29 of the most important ionization stages, in particular C, N, O and Fe using accurate atomic data; the approxim…
Model atmospheres for Vega.
Castelli, F.; Kurucz, R. L.
We compared blanketed Local Thermodynamic Equilibrium (LTE) models for Vega computed both with the opacity distribution function (ODF) method and the opacity-sampling (OS) method. In the ODF case we used the ATLAS9 code with the new opacity data from Kurucz (1992). Model parameters for Vega depend on the amount of reddening and on the helium abund…
Ulysses field and plasma observations of magnetic holes in the solar wind and their relation to mirror-mode structures
Goldstein, Bruce E.; Neugebauer, Marcia; Smith, Edward J. +3 more
The term ``magnetic hole'' has been used to denote intervals when the magnitude of the interplanetary magnetic field drops to a few tenths, or less, of its ambient value for a time that corresponds to a linear dimension of tens to a few hundreds of proton gyro-radii. Data obtained by the Ulysses magnetometer and solar wind analyzer have been combi…
Steps toward Determination of the Size and Structure of the Broad-Line Region in Active Galactic Nuclei. V. Variability of the Ultraviolet Continuum and Emission Lines of NGC 3783
Altieri, B.; Mazeh, T.; Shull, J. M. +61 more
We report on the results of intensive ultraviolet spectral monitoring of the Seyfert 1 galaxy NGC 3783. The nucleus of NGC 3783 was observed with the International Ultraviolet Explorer satellite on a regular basis for a total of 7 months, once every 4 days for the first 172 days and once every other day for the final 50 days. Significant variabili…
The Balmer-dominated Northeast Limb of the Cygnus Loop Supernova Remnant
Blair, William P.; Raymond, John C.; Hester, J. Jeff
We present a comprehensive investigation of the Balmar-dominated northeast limb of the Cygnus Loop supernova remnant. Data presented include H alpha (O III), and X-ray images, UV and visible spectrophotometry, and high-resolution spectroscopy. The two relatively bright Balmer-dominated filaments visible on the POSS prints are seen to be part of a …