Search Publications
The High-Luminosity BL Lacertae Object PKS 0823-22
Falomo, Renato
Simultaneous infrared, optical, and UV observations of the BL Lacertae object PKS 0823-22 are presented. The identification of the observed absorption doublet at λλ5341, 5355 with Mg II λλ2796, 2803 gives an absorption redshift z_abs_ = 0.910. At this redshift, the object is one of the most luminous of its class with M_V_ <~ -29.4. The spectral…
Detection of Trace Helium in G104-27, a 26,000 K DA White Dwarf
Wesemael, F.; Holberg, J. B.; Kidder, K. M.
The detection of the He I 4471 A feature in the moderately hot DA white dwarf G104 - 27 places this star within the rather sparse class of DAB white dwarfs. It does not appear possible, on the basis of the present data, to distinguish between a stratified and a homogeneously mixed atmosphere. While a stratified structure would be natural for a DA …
Small-Scale Structure in the Diffuse Interstellar Medium
Meyer, David M.
The initial results of a study to probe the small-scale structure in the diffuse interstellar medium (ISM) through IUE and optical observations of interstellar absorption lines toward both components of resolvable binary stars is reported. The binaries (Kappa CrA, 57 Aql, 59 And, HR 1609/10, 19 Lyn, and Theta Ser) observed with IUE have projected …
Simultaneous X-Ray, Ultraviolet, and Optical Observations of LMC X-3
Maraschi, L.; Tanzi, E. G.; Belloni, T. +7 more
The black hole candidate LMC X-3 was observed simultaneously at X- ray (Ginga), UV (IUE), and optical frequencies in 1988 January. The X- ray energy distribution is the superposition of a thermal component and a hard tail. The former component can be described equally well by a Comptonization spectrum or by a disk blackbody. In the latter picture,…
Ultraviolet Observations of NGC 205
Bertola, Francesco; Wilcots, Eric M.; Hodge, Paul +2 more
Low-resolution IUE observations of the dwarf elliptical galaxy NGC 205 show that the UV spectral energy distribution of the galaxy is relatively flat. Spectra centered on the nucleus and on a region north of the nucleus show evidence of recent "bursts" of star formation which contribute strongly to the UV spectral energy distribution. We fit the U…
EXOSAT Observations of Cygnus X-2 Continuum and Line Spectrum
Maraschi, L.; Tanzi, E. G.; Chiappetti, L. +7 more
An analysis of five Exosat observations of Cyg X-2, taken around a full binary orbit is presented. The data were obtained using all instrumentation (1000 lines/mm Transmission Grating Spectrometer, Channel Multiplier Array + filters, Medium-Energy experiment, and Gas Scintillation Proportional Counter) simultaneously, and span the full energy rang…
X-Ray and Ultraviolet Observations of the Seyfert Galaxy MCG 8-11-11
Maraschi, L.; Tanzi, E. G.; Chiappetti, L. +4 more
MCG 8-11-11 was observed in the 0.5-8 keV band with the EXOSAT observatory at 9 epochs in 1983-1986. Quasi-simultaneous UV observations were obtained in all but one case. The X-ray spectra are well fitted by absorbed power laws (N_H_ ~ 1.5 x 10^21^ cm^-2^, α_ph_ ~ 1.7). Small variations of the spectral shape are found with softening of the source …
An Evolving Relativistic Jet Model for the BL Lacertae Object Markarian 421
Kondo, Y.; Urry, C. M.; Hutter, D. J. +2 more
Coordinated observations of the nearby BL Lacertae object Mrk 421 obtained during 1980 May, 1984 January, and 1984 March are described. These observations give a time-frozen picture of the continuous spectrum of Mrk 421 at X-ray, ultraviolet, optical and radio wavelengths. The observed spectra have been fitted to an inhomogeneous relativistic jet …
A New Powerful Test for Periodic Pulsed Emission of High-Energy Photons
Swanepoel, J. W. H.; de Beer, C. F.
A novel stastistical test devised for detecting periodic pulsations in a series of photon arrival times is found to perform powerfully in the detection of multiple, narrow peaked light curve shapes against a uniform background, especially if the light curve has multiple peaks. The statistical test has been applied to observations of the first 1350…
Hot Degenerates in the MCT Survey. I. MCT 0130-1937, a New, Color-selected PG 1159 Object
Kepler, S. O.; Fontaine, G.; Wesemael, F. +4 more
In the course of a survey for high-latitude, UV excess objects in the Southern Hemisphere, a new white dwarf star belonging to the PG 1159 spectroscopic class was discovered. A variety of spectroscopic observations show this object to be similar to the prototype PG 1159 - 035 in exhibiting He II, C IV, and O VI features in its optical spectrum, as…