Search Publications
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…
Additional Constraints on Circumstellar Disks in the Trapezium Cluster
Stauffer, John R.; Prosser, Charles F.; Hartmann, Lee +1 more
We discuss the new constraints on the population of compact ionized sources in the Trapezium Cluster thought to arise from the ionization by the central OB stars of circumstellar disks around low-mass pre-main sequence stars. We present new Hubble Space Telescope (HST) Planetary Camera observations of two of these candidate disk sources, resolving…
RE 1738+665: the hottest DA white dwarf detected by ROSAT.
Barstow, M. A.; Koester, D.; Sansom, A. E. +6 more
One of the most important results of the ROSAT all-sky X-ray and EUV surveys has been the discovery of a large number of previously uncatalogued white dwarfs. One of these, RE 1738+665, is found to be the hottest hydrogen-rich DA white dwarf detected, with a temperature of 88000 K and log g =7.8, lying significantly above the 70000-K observational…
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…
Lower chromospheric activity in low activity M dwarfs
Doyle, J. G.; Mathioudakis, M.; Houdebine, E. R. +1 more
Four low activity dM(e) stars Gl 105B, Gl 643, Gl 813 and Gl 821 were observed spectroscopically in the optical and ultraviolet regions. Despite relatively long integrations, only one of the four had detectable Ca II K&H emission, Gl 821, which had an observed flux of 9 10^-15^ erg/cm2/s, giving a surface flux of only 0.8 10^4^ erg/cm2/s. Simi…
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…
Analysis of ROSAT pointed observations of 15 hot DA white dwarfs.
Wolff, B.; Jordan, S.; Koester, D. +1 more
We present the results of pointed observations of hot white dwarfs with the ROSAT PSPC detector, and through the P1 filter of the Wide Field Camera. Model atmospheres containing hydrogen and helium, either homogeneously mixed or chemically stratified, are used to analyze the new data together with observations of the same objects by EXOSAT and the…