Search Publications
On the nature of rapid X-ray variability in active galactic nuclei.
McHardy, I. M.; Lehto, H. J.; Green, A. R.
We systematically analyse all (110) EXOSAT AGN medium-energy light curves of length greater than 20 ks to search for and quantify their flux variability. We also perform extensive simulations to quantify the selection effects (such as the source brightness or the length of observation) that might prevent the detection of variability. We quantify v…
ROSAT studies of the composition and structure of DA white dwarf atmospheres.
Barstow, M. A.; Koester, D.; Sansom, A. E. +7 more
We present here a detailed study of a sample of hot I)A white dwarfs detected in the EUV and soft X-ray bands by ROSAT during its all-sky survey. The survey data are combined with additional ROSAT pointed-phase observations, earlier EXOSAT results and the available optically determined effective temperatures and gravities. We show that the spectra…
Further probing of the X-ray source in NGC 4151 : new constraints on the nuclear geometry.
Sokoloski, J. L.; Yamauchi, M.; Warwick, R. S. +4 more
We report on the results of new Ginga observations of the archetypal Seyfert galaxy, NGC 4151, performed over an 18-month period between early 1990 and mid-1991. The present programme complements earlier extensive monitoring of this source in the medium-energy X-ray band by both EXOSAT and Ginga to give a combined data set of some 36 separate obse…
New light on UU Sagittae.
Pollacco, D. L.; Bell, S. A.
New V- and I-band CCD photometry and medium-resolution spectroscopy are used to derive the masses and radii accurate to less than 10 percent for the individual components of the eclipsing central star of the planetary nebula Abell 63 - UU Sge. Emission lines from the secondary component and He II and N V absorption features from the primary compon…
New detections of Ly-alpha emission in young galaxies.
Terlevich, Roberto; Terlevich, Elena; Diaz, Angeles I. +1 more
We report IUE observations of two extremely low-metallicity H II galaxies. Ly α emission was detected in both galaxies. Our results confirm previous findings that young or unevolved galaxies exhibit weak or absent Ly α emission combined with a strong UV continuum, and that the Ly α/Hβ ratio and metal content are correlated in the sense that the lo…
On the nature of the blue light in central cluster galaxies.
Fabian, A. C.; Crawford, C. S.
An excess blue component of light, extended over the innermost few kpc, is observed in several central cluster galaxies. Using a combination of blue optical spectra and IUE data, we show that the spectrum of the excess blue light is consistent with both star formation dominated by the light of B5 stars, and power-law spectra with slopes between λ^…
X-ray orbital modulations in intermediate polars.
Hellier, Coel; Mason, Keith O.; Garlick, Mark A.
A systematic search of the EXOSAT observations of intermediate polars has revealed that a majority of systems show orbital-cycle X-ray modulations. The modulations are irregular, have the characteristic energy dependence of photoelectric absorption and, where it can be determined, have minima preferentially at orbital phase about 0.8. We remark on…
A detailed X-ray and radio study of the supernova remnant W 44.
Angelini, Lorella; Jones, L. R.; Smith, A.
We analyze EXOSAT and Einstein Observatory X-ray spectra, an Einstein X-ray image, and a detailed VLA radio map of the SNR W44. The diffuse soft X-ray emission, which is only observed from the interior of the SNR, is shown to be largely of thermal origin. The absence of soft X-ray emission from the shell can be explained by the measured line-of-si…
The soft X-ray excesses of high-luminosity AGN.
Saxton, R. D.; Turner, M. J. L.; Ohashi, T. +3 more
LE and ME spectra of 12 quasars from the EXOSAT data base have been analysed in a search for soft excesses. We have been able to quantify the soft excesses more accurately by using spectral indices for the ME taken from the much more sensitive Ginga observations of the same quasars. Eight quasars show a significant soft excess and the remaining fo…
IK Peg : a nearby, short-period, Sirius-like system.
Stickland, D. J.; Kellett, B. J.; Wonnacott, D.
The system IK Peg has been known to be a binary for over 60 years but the secondary has never been identified. The detection of this system in the British Wide Field Camera All-Sky Survey in the EUV has enabled the secondary to be positively identified as a white dwarf. Fits to EUV survey data, the first IUE spectrum, and archival X-ray data indic…