Search Publications
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…
Optical, IUE, and ROSAT Observations of the Eclipsing Nova-like Variable V347 Puppis (LB 1800)
Raymond, John C.; Buckley, David A. H.; Mauche, Christopher W. +5 more
Using time-resolved optical spectroscopy and UBVRI and high-speed photometry obtained at Mount Stromlo Observatory, Mount John University Observatory, and the South African Astronomical Observatory; International Ultraviolet Explorer (IUE) ultraviolet spectroscopy; and Roentgen Satellite (ROSAT) survey X-ray fluxes, we present a study of the accre…
Interstellar and Intergalactic Magnesium and Sodium Absorption toward SN 1993J
Bowen, David V.; Meyer, David M.; Roth, Katherine C. +1 more
We present echelle-resolution (FWHM ~ 5 km s^-1^) HST observations of Mg II, Mg I, and ground-based observations of Na I absorption toward SN 1993J which exploded in M81. We detect individual absorption components spanning a total velocity range of -163 < ν_sun_ < +225 km s^-1^. The components are grouped into three subcomplexes, representin…
GHRS Spectroscopy of Individual Stars in R136a
Hubeny, Ivan; Heap, Sara R.; Malumuth, Eliot M. +3 more
The installation of the Corrective Optics Space Telescope Axial Replacement (COSTAR) Instrument on the Hubble Space Telescope (HST) makes it possible to observe stars in very crowded regions with high spatial and spectral purity. To demonstrate this capability, we have used the Goddard High Resolution Spectrograph (GHRS) to obtain spectra of two s…
ROSAT Observations of Cataclysmic Variables: A Search for the Boundary Layer Emission
Raymond, J. C.; Vrtilek, S. D.; Patterson, J. +1 more
Many cataclysmic variables (CVs) and low-mass X-ray binaries show He II line emission at wavelength 1640 and wavelength 4686. As recombination lines of an ion requiring 55 eV for ionization, these lines cannot be attributed to gravitational heating in the disk but could be due to reprocessed 55-280 eV X-rays which may be produced in a boundary lay…
Classical Cepheids with Terminal Age Main-Sequence Companions: Constraints on Evolution
Evans, Nancy Remage
Eight binaries containing a Cepheid and a hot companion evolved beyond the ZAMS are studied using IUE spectra. The spectral types of these TAMS (terminal age main-sequence) companions are determined from the spectra and absolute magnitudes are determined from the magnitude difference between the two stars and the absolute magnitude of the Cepheid.…