Search Publications
Hubble Space Telescope Imaging of Super--Star Clusters in NGC 1569 and NGC 1705
O'Connell, Robert W.; Gallagher, John S., III; Hunter, Deidre A.
We examine the structural properties of three super-star clusters in the nearby, H I-rich galaxies NGC 1569 and NGC 1705. The clusters, which have total absolute V magnitudes between - 13.3 and - 14.1, appear to be point sources on ground-based images but are partially resolved in new images obtained with the Hubble Space Telescope (HST) Planetary…
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…
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 …
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 …
Discovery of Cepheids in IC 4182: Absolute Peak Brightness of SN IA 1937C and the Value of H 0
Panagia, N.; Saha, A.; Labhardt, Lukas +4 more
Repeated imaging of a field in the Sdm galaxy IC 4182 with the Wide Field Camera of the Hubble Space Telescope has led to the discovery of 28 Cepheid variables. The distance modulus to this galaxy, derived from the Cepheids, is (m - M) = 28.36 +/- 0.09, and the absolute magnitude at peak brightness of the Type Ia supernova SN 1937C which appeared …
The 1993 Multiwavelength Campaign on 3C 279: The Radio to Gamma-Ray Energy Distribution in Low State
Maraschi, L.; Ghisellini, G.; Pian, E. +27 more
Simultaneous observations of 3C 279 at radio, millimeter, near- infrared, optical, ultraviolet (with IUE) and X-ray (with ROSAT) wavelengths were obtained in 1992 December-1993 January, during a three week pointing at the source by the Compton Gamma Ray Observatory. The blazar was in a quiescent or "low" state during this period. Comparing the mul…
Evolution of Lyman-Limit Absorption Systems over the Redshift Range 0.40 < Z < 4.69
Irwin, M. J.; McMahon, R. G.; Storrie-Lombardi, L. J. +1 more
We present the results of a study of 15 z > 4.2 QSOs that extend statistical studies of Lyman-limit absorption line systems [N(H I) >= 1.6 x 10^17^ cm^-2^] to the highest redshifts currently possible. This data set has been combined with homogeneous data sets of low-redshift Hubble Space Telescope observations and intermediate- redshift grou…
A Spectroscopic Analysis of DAO and Hot DA White Dwarfs: The Implications of the Presence of Helium and the Nature of DAO Stars
Fontaine, G.; Bergeron, P.; Wesemael, F. +4 more
A comprehensive study of optical spectrophotometry of DAO white dwarfs is presented. A detailed analysis of the He II lambda 4686 line profiles demonstrates conclusively that the chemical composition in the atmospheres of DAO stars is not stratified, except in one object (PG 1305-017). On the other hand, line profiles calculated from models with h…
M Dwarfs, Microlensing, and the Mass Budget of the Galaxy
Gould, Andrew; Bahcall, John N.; Kirhakos, Sofia +1 more
We show that faint red stars do not contribute significantly to the mass budget of the Galaxy or to microlensing statistics. Our results are obtained by analyzing two long exposures of a high-latitude field taken with the Wide Field Camera on the newly repaired {\it Hubble Space Telescope}. Stars are easily distinguished from galaxies essentially …