Search Publications
GK Per : X-ray observations in quiescence.
King, A. R.; Watson, M. G.; Norton, A. J.
Two X-ray observations of GK Per in quiescence made with Exosat are presented. The X-ray light curve obtained on both occasions shows clear evidence for the 351-s pulse period first discovered during an earlier outburst. The pulse profile in the first of the two quiescent observations is similar to that observed during outburst, albeit with lower …
Spectroscopy of the M 15 X-ray source : discovery of binary motion and an unusual systemic velocity.
Charles, P. A.; Hassall, B. J. M.; Naylor, T. +1 more
The authors present the first phase-resolved optical spectroscopy of AC 211, the optical counterpart of the X-ray source in the core of M15. The spectrum is dominated by the variable and complex He II λ4686 emission, but the authors have also found He I in absorption. By following the motion of He I λ4471 they have discovered the binary period to …
Variable low-energy absorption in the X-ray spectrum of ESO 103-G35.
Turner, T. J.; Warwick, R. S.; Pounds, K. A.
EXOSAT observations of the Seyfert 1.9 galaxy, ESO 103-G35, have revealed that this source has a heavily absorbed and variable low-energy X-ray spectrum. Specifically the inferred column density was observed to decrease from ~1.7x10^23^ to ~1.0x10^23^ cm^-2^ over a 90-day period. This variation is interpreted in terms of an X-ray absorbing screen …
Regular orbital variations in the ultraviolet resonance lines of YZ Cnc.
Verbunt, Frank; Drew, Janet E.
Observations with the International Ultraviolet Explorer of the dwarf nova YZ Cnc show regular orbital variations in the line profiles of the ultraviolet resonance lines. The P Cygni profile of the C IV λ1549 line changes drastically from absorption-dominated to emission-dominated, during the three observed orbits in each of two observation shifts…
Observations of three high-state eclipse egresses of Hercules X-1.
Fabian, A. C.; Tennant, A. F.; Day, C. S. R.
EXOSAT data from three high-state egresses of the pulsating X-ray binary Her X-1 are presented. Analysis of these data indicates that the extended atmosphere of the companion is the most likely explanation of the extent of the egresses. By fitting spectra taken from the egresses the authors find that the atmosphere has an exponential structure. If…
EXO 023432-5232.3 - an eclipsing AM Herculis binary.
Cropper, Mark; Bailey, Jeremy; Hough, J. H. +1 more
The authors report observations of the serendipitous EXOSAT source EXO 023432-5232.3 which confirm that the object is an AM Herculis type binary and show the presence of eclipses by the companion star. From high-speed photometry of the eclipses they deduce that the cyclotron emission region is less than one seventh the size of the white dwarf. Fro…
Quasi-periodic oscillations in the bright galactic bulge X-ray sourceGX 340+0.
van Paradijs, J.; van der Klis, M.; Lewin, W. H. G. +4 more
Quasi-periodic oscillations (QPOs) have been detected in the X-ray flux of the bright Galactic bulge X-ray source GX 340+0. The QPO, the associated red noise, and their relation to the spectral state of the source are described. The QPO behavior is found to be similar to that seen in Cyg X-2 and GX 5-1.
The excitation of SI emission lines in chromospheres of late-type giant stars.
Judge, P. G.
Constraints on the structure of the chromospheres of Alpha Boo, Alpha Tau, and Beta Gru derived from high-resolution IUE spectra are used to investigate the excitation mechanisms of emission lines of neutral sulfur, which are prominent in IUE spectra of late-type giant and supergiant stars. Observational data for the S I lines from other studies a…
Flare activity on UV Ceti : visible and IUE observations.
Bromage, G. E.; Dufton, P. L.; Keenan, F. P. +2 more
Simultaneous far-ultraviolet (IUE) spectroscopy and optical photometry and spectrophotometry of a flare on UV Ceti are reported. The flare reached ΔU = 2 mag but showed only modest enhancements in the IUE spectra. The optical spectrophotometry indicated broadened Balmer line profiles during the flare, with Hβ and Hγ clearly showing red wings (≡100…
The ultraviolet continuum of quasars -II. Continuum variability.
Wilson, R.; Gondhalekar, P. M.; O'Brien, P. T.
We present data on the variability of the ultraviolet continuum for a large sample of quasars observed with IUE. No variability was found on time- scales of days, but is common on time-scales of weeks to months. There is no correlation between the two-folding time-scale and luminosity, although the sampling rate is poor. For most of the quasars th…