Search Publications
Dramatic X-ray variability in the narrow emission line galaxy NGC 7314.
Turner, T. J.
EXOSAT observations of the narrow emission line galaxy NGC 7314 have shown remarkable variability in the 2 - 10 keV band of the medium energy (ME) detectors. The most obvious feature in the ME light curve is a factor of 4 increase in the count rate over 5000 s, with some evidence for a softening of the spectrum as the source brightened. The lack o…
Delta Andromedae (K3III) : an IRAS source with an unusual ultraviolet spectrum.
Judge, P. G.; Jordan, C.; Rowan-Robinson, M.
The IRAS survey has revealed anomalous cool infrared emission from a number of otherwise apparently normal K stars. IUE spectra of the brightest of these stars, Delta And, which is a spectroscopic binary and optical standard K3 III star, is obtained. The IUE spectra show the unexpected presence of C IV in emission, implying hot material (about 100…
Non-radial pulsations in the extreme helium star HD 160641.
Jeffery, C. S.; Kilkenny, D.; Lynas-Gray, A. E. +1 more
Mean periods of 0.35±0.01, 0.71±0.05, 1.12±0.13 and 1.77±0.34 day are identified from separately analysed photometric observations (obtained in 1979 and 1982) of the extreme helium star HD 160641. Radial velocities were obtained simultaneously with photometry on three nights in 1982. Optical variations are not accompanied by detectable colour chan…
Observations of a partial X-ray eclipse in the long-period low mass X-ray binary 2S 0921-630.
Branduardi-Raymont, G.; Mason, K. O.; Cordova, F. A. +1 more
A partial eclipse of the X-ray flux from 2S 0921-630 has been recorded for the first time, using the EXOSAT satellite. The time of the X-ray eclipse agrees with an extrapolation of the ephemeris of optical dips in 2S 0921-630, strongly supporting the hypothesis that 2S 0921-630 is an eclipsing binary with a period of just over 9 day. The X-ray ecl…
An EXOSAT observation of the bursting X-ray transient 4U 1608-52.
Stella, L.; White, N. E.; Barr, P. +1 more
An EXOSAT observation of the transient X-ray burster 4U 1608-52 detected the source in a low state. The spectrum of the persistent emission is a power law with a photon index of 1.9 similar to that from other X-ray burst sources. During the 5.5 hr exposure a double-peaked type I burst was seen. A detailed spectral analysis shows this to be caused …
The stellar winds of early-type stars in the Small Magellanic Cloud.
Prinja, Raman K.
Low-resolution IUE spectra are used to investigate stellar winds of early-type stars in the Small Magellanic Cloud (SMC). Model profiles are used to fit well developed P Cygni doublets noted in 25 main-sequence, giant, and supergiant stars. Terminal velocities in the SMC are found to be, generally, up to a factor of 2 lower relative to galactic O …
A pulse timing study of the X-ray pulsar 4U 1145-619.
Warwick, R. S.; Cook, M. C.
EXOSAT observations of the X-ray pulsar 4U1145-619, which is known to exhibit X-ray outbursts on an apparently regular 187-day cycle, have revealed a rapid decrease in the pulse period during the outburst states, whereas on longer time-scales the pulse period is found to be stable. The X-ray luminosity is too low, even during outburst, to account …
EXOSAT observations of the X-ray source in M 15.
Fabian, A. C.; Tennant, A. F.; Redfern, R. M. +2 more
The results from two long Exosat observations of the X-ray source in the globular cluster M15 (NC 7078), totalling approximately 1 d and separated by 100 d, are reported. Variability is detected on timescales down to 250 s, but no variations attributable to an eclipse were observed, which is surprising in view of the large fluctuations reported by…
Power spectra, with application to EXOSAT data.
Tennant, A. F.
It is shown how an instrumental effect, coupled with the on-board computer sampling, affects the pulse-height analysis data obtained from Exosat, and analytic expressions are developed to remove these effects from the data for the case of small source variability. In the method, the expectation of the power spectrum is the Fourier transform of the…
X-ray spectrum of sigma Geminorum : an RS Canum Venaticorum type binary.
Singh, K. P.; Westergaard, N. J.; Schnopper, H. W. +4 more
The binary system Sigma Gem has been observed on three occasions during 1984 November 17-21 with the medium-energy and the low-energy detectors on the Exosat Observatory. Spectral analysis of the data obtained over the energy range of 0.05-6.0 keV shows evidence for a bimodal temperature distribution of emission measure in an optically thin therma…