Search Publications
The Discovery of 0.2 HZ Quasi-periodic Oscillations in the X-Ray Flux of the Transient 42 Second Pulsar EXO 2030+374
Stella, L.; Parmar, A. N.; Angelini, L.
The discovery of about 0.2 Hz quasi-periodic oscillations (QPOs) in the 1-15 keV X-ray flux of the transient 42 s pulsar EXO 2030 + 375 is reported. The detection of QPOs in the power spectra of this pulsar was made possible by the application of a newly developed technique to decouple the power spectrum peaks. QPOs were detected during an outburs…
An EXOSAT X-Ray Observation of One Orbital Cycle of 4U 1700-37/HD 153919
Haberl, F.; White, N. E.; Kallman, T. R.
Exosat observations of close to one complete binary cycle of 4U 1700-37/HD 153919 are presented, and X-ray absorption variations are determined as a function of orbital phase in order to study the properties of the stellar wind of the companion HD 153919. The decrease noted in absorption between eclipse egress and phase 0.5 may be due to X-rays fr…
The Kinematics of Milky Way Halo Gas. I. Observations of Low-Ionization Species
Danly, Laura
Ultraviolet interstellar line day observed with the IUE toward 70 halo stars and four extragalactic sight lines are analyzed in a study of the large-scale kinematic properties of the Milky Way halo gas. The motions of the low-ionization gas is focused on. Large systematic velocities are found, and a pronounced asymmetry in the absorption character…
X-Ray Observations of the Starburst Galaxy M82
Pietsch, W.; Schaaf, R.; Kronberg, P. P. +2 more
We report here on long (~ 10^5^ s) X-ray observations of the starburst galaxy M82 with the European X-ray satellite EXOSAT. The observations with the low-energy imaging instrument confirm that there is extended X-ray emission from above and below the disk, with an overall extent perpendicular to the disk of almost 6' corresponding to 6 kpc. We pre…
A Soft X-Ray Survey of Hot White Dwarfs with EXOSAT
Heise, J.; Paerels, F. B. S.
Broadband multicolor soft X-ray photometry of 34 hot white dwarfs is presented, obtained with the Low Energy Imaging Telescopes on Exosat. By combining the soft X-ray fluxes with measurements of the stellar parameters in the UV and optical bands, photospheric He abundances for 16 of the 21 hot DA white dwarfs are derived. Supplemented by five star…
Emission-Line Variability of Fairall 9: Determination of the Size of the Broad-Line Region and the Direction of Gas Motion
Koratkar, Anuradha P.; Gaskell, C. Martin
A cross-correlation analysis has been performed on 118 IUE spectra of Fairall 9 available from 1978 to January 1987 to determine the size of the broad-line region and the average direction of gas motion. Analysis of the line flux shows that the C IV λ1549 emitting region is 124 +/- 39 light days from the central source and the Mg II λ2800 emitting…
UV Fluorescence of Molecular Hydrogen and Red Dust Emission in the Gamma Cassiopeiae Nebulae IC 63
Bohlin, Ralph C.; Witt, Adolf N.; Stecher, Theodore P. +1 more
Resonant fluorescence of molecular hydrogen has been observed in the reflection nebula IC 63 with the IUE satellite. Both the noncoherent resonant scattering and the dissociative continuum are shown to agree well with molecular theory. Extended red emission is also found in this nebula and may be physically related to the dissociation of H2.
Simultaneous X-Ray, Ultraviolet, and Optical Observations of the BL Lacertae Object PKS 2155-304
Maccagni, D.; Maraschi, L.; Tanzi, E. G. +6 more
X-ray observations of PKS 2155-304, performed at nine epochs in 1983-1985 with the EXOSAT satellite, are reported. The source was observed quasi-simultaneously in the far-UV with IUE, and in the optical and infrared with ESO telescopes. X-ray light curves with 400 s time resolution are derived. On two occasions the flux showed a rapid regular risi…
Two X-Ray--selected BL Lacertae Objects Observed with the HEAO 1 Scanning Modulation Collimator
Buckley, D. A. H.; Schwartz, D. A.; Tapia, S. +4 more
We have discovered two 16th magnitude BL Lac objects, H1101-232 and H1426+428, during an ongoing program to identify the optical counterparts of X-ray sources from the HEAO 1 survey. Each is a persistent and relatively bright X-ray source that was also detected by the Uhuru and Ariel 5 surveys. Our classifications are based on the combined observa…
Coronal Activity in F-, G-, and K-Type Stars. IV. Evidence for Expanding Loop Geometries in Stellar Coronae
Mewe, R.; Schrijver, C. J.; Lemen, J. R.
A detailed analysis is presented of X-ray spectra of Capella and of Sigma2 CrB. The spectra of both stars are compatible with coronae consisting of two different ensembles of static loops with different maximum temperatures and ratios of the cross sectional areas at the loop top and at the footpoint. The cool (5 MK) loop components in both stars s…