Search Publications
Remarkable Long-Term Changes in the Small Magellanic Cloud Wolf-Rayet System HD 5980
Koenigsberger, G.; Auer, L. H.; Moffat, A. F. J. +3 more
In this paper we report the remarkable changes which occurred in the Small Magellanic Cloud W-R system HD5980 = AB5 between 1978 and 1991. Within this timescale, there has been a systematic enhancement (by factors of 2-10 depending on the line) in the equivalent widths of all emission lines, and a change in the relative strengths of N III, N IV, a…
Eclipse Mapping of the Accreting Magnetic White Dwarf in DP Leonis with HST
Holberg, J. B.; Liebert, James; Schmidt, Gary D. +1 more
We present time-resolved ultraviolet spectrophotometry of the AM Her system DP Leo (E1114+182), obtained with the Faint Object Spectrograph on the Hubble Space Telescope (HST) in 1991 October. During this period, the binary was in a low-activity state. Complementary optical spectrophotometry and spectopolarimetry were obtained in 1991 October and …
Ultraviolet Interstellar Polarization Observed with the Hubble Space Telescope
Martin, P. G.; Walsh, J. R.; Nandy, K. +9 more
We have used the Faint Object Spectrograph of the Hubble Space Telescope to observe interstellar linear polarization from 1300 to 3300 A in two stars with well-studied interstellar polarization at visible wavelenths. The wavelength dependence of linear polarization declines smoothly with decreasing wavelength and is devoid of structure associated …
Spectral Energy Distributions of the Brightest Palomar-Green Quasars at Intermediate Redshifts
Tripp, Todd M.; Green, Richard F.; Bechtold, Jill
We have combined low-dispersion International Ultraviolet Explorer (IUE) spectra with the optical/near-IR spectrophotometry of Neugebauer et al. (1987) in order to study the spectral energy distributions of seven of the brightest Palomar-Green quasars at intermediate redshifts (0.9 <= z_em_ <= 1.5). Some of these PG quasars are barely detect…
High-Resolution Optical and UV Observations of the Centers of NGC 1316 and NGC 3998 with the Hubble Space Telescope
Fabbiano, G.; Trinchieri, G.; Fassnacht, C.
B and UV high-resolution images obtained with the HST FOC reveal centrally increasing surface brightness and UV-bright point sources at the nuclei of the early-type galaxies NGC 1316 and NGC 3998. Model fitting of the surface brightness distribution does not exclude a central flattening, which could however be the result of extinction and/or of im…
The Near-Infrared--Optical--Ultraviolet Emission of BL Lacertae Objects
Pian, E.; Falomo, R.; Treves, A. +1 more
Near-infrared, optical, and ultraviolet quasi-simultaneous observations of 11 BL Lacertae objects are reported. For all but one source the dereddened spectral flux distribution in the (8 x 10^13^)-(2 x 10^15^) Hz frequency range can be described by a single power law f_v_ is proportional to ν^-α^ with average spectral index <a> = 0.88 +/- 0.…
Line Profile Variations from Atmospheric Eclipses: Constraints on the Wind Structure in Wolf-Rayet Stars
Koenigsberger, G.; Auer, L. H.
Binary systems in which one of the components has a stellar wind may present a phenomenon known as 'wind' or 'atmospheric eclipse', in which that wind occults the luminous disk of the companion. The enhanced absorption profile, relative to the spectrum at uneclipsed orbital phases, can be be modeled to yield constraints on the spatial structure of…
Star Formation in NGC 4449: MAMA-Detector UV Imagery and Fabry-Perot Balmer-Line Imagery
Hill, Robert S.; Smith, Andrew M.; Bruhweiler, Fred C. +4 more
Using far-ultraviolet (FUV) and Balmer-line imagery, we investigate the star formation history of 22 large OB complexes in the Magellanic irregular galaxy NGC 4449. The FUV luminosity of NGC 4449 is comparable to those of late-type spirals and is greater than that of the LMC by 2.4 mag, indicating substantial star formation in the last 10^8^ yr. F…
Rapid Searches for Counterparts of GRB 930131
Schaefer, Bradley E.; Coe, M. J.; Ricker, George R. +39 more
A fading counterpart to a gamma-ray burst (GRB) would appear as a point source inside a GRB error region soon after the burst which dims on a timescale from minutes to days. The favorable circumstances of the burst GRB 930131 allowed for an international campaign to search for fading counterparts starting 6.8 hr after the burst. We report observat…
GD 323: New Observations and Analysis of the Prototype DAB White Dwarf
Koester, D.; Saffer, Rex A.; Liebert, James
In this paper we present new spectroscopic observations of very high quality of the hybrid DAB white dwarf GD 323. GD 323 shows both hydrogen and helium lines and is located at an effective temperature (approximately equals 28,750 K), which places it at the hot end of the DB sequence just below the empirical DB gap. With recent results for the rel…