Search Publications
X-ray observations of the 50-min dipping source XB 1916-053.
Mason, Keith O.; Smale, Alan P.; White, Nick E. +1 more
Three EXOSAT observations of the low-mass X-ray binary XB 1916-053 have revealed extreme variability in the appearance of the dips, ranging from complete absence to two broad, deep dips per 50-min cycle. These dips are believed to result from the obscuration of the central X-ray source by azimuthal structure in the accretion disc. The X-ray spectr…
X-ray and ultraviolet observations of Markarian 421.
Bromage, G. E.; Warwick, R. S.; George, I. M.
We present the results of a detailed study of the BL Lacertae type object Markarian 421 (Mrk 421) based upon EXOSAT and IUE observations made during 1984 and 1985. In the X-ray band Mrk 421 exhibits significant variability on time-scales typically of the order of a day with a minimum e-folding time-scale, t_v_, of ~5x10^4^s. There is some indicati…
Far-ultraviolet absorption lines in active galaxies.
Ulrich, M. -H.
Attention is drawn to the far-ultraviolet absorption lines which have been discovered with IUE in a number of active nuclei. The properties of these lines are presented and discussed with emphasis on the following points: (i) the frequency of occurrence of far ultraviolet absorption lines (ii) a comparison between the properties of these lines and…
EXOSAT observations of variable coronal X-ray emission from the youngK dwarf AB Doradus (= HD 36705).
White, N. E.; Collier Cameron, A.; Bedford, D. K. +2 more
We present the results of a search for rotationally-modulated X-ray emission from the young KO dwarf AB Doradus, using the low- and medium-energy detectors on board the EXOSAT spacecraft. Two sets of observations were obtained, each covering all or nearly all of the 0.514 day rotation period of the star, in 1984 December and 1986 January. A single…
Spectral energy distributions of galaxies in high-redshift clusters. III. Abell 370 at z=0.37.
Ellis, Richard S.; Couch, Warrick J.; MacLaren, Iain
We have imaged the distant cluster Abell 370 (z=0.37) with a CCD- based intermediate pass-band multicolour system defined in earlier papers in this series. Our technique is to use such colours to classify faint galaxies in redshift and spectral class without recourse to spectroscopic data. We demonstrate from a new comparison of ~80 spectra gather…
Very extended ionized gas in radio galaxies - IV. PKS 2152-69.
Snijders, M. A. J.; di Serego Alighieri, S.; Fosbury, R. A. E. +5 more
Optical, radio and ultraviolet observations of the luminous southern radio elliptical galaxy PKS 2152-69 are presented. Narrow-band images and long-slit spectra reveal a system of low-ionization filaments extending out to a maximum radius of 20 arcsec (16kpc; H_0_=50 km s^-1_ Mpc^-1^ as used throughout this paper). To the north-east, however, a lu…
Observational evidence for mass loss from classical cepheids.
Deasy, H. P.
This paper examines the evidence for mass loss from classical Cepheid variables in the light of recent observational studies of infrared and ultraviolet emission from these objects. Mass-loss rates derived for several stars range between 10-10M_sun;yr-1 and 10-6M_sun;yr-1. The lower end of this range pro…
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 …