Search Publications
Boundary-layer temperatures in high accretion rate cataclysmic variables.
Drew, Janet E.; Hoare, Melvin G.
The Zanstra method is used to derive limits on boundary-layer temperatures in eclipsing dwarf novae during outburst and nova-like variables, using the observed He II 1640 and 4686 A recombination lines. It is assumed that all the emission is produced in the wind rather than the accretion disk. This method constrains the boundary-layer temperatures…
Two early-type POST AGB stars at high galactic latitudes.
Dufton, P. L.; Keenan, F. P.; Conlon, E. S. +1 more
Two high galactic latitude B-type stars, PHL 1580 and PHL 174, originally identified as distant early-type objects from low-resolution spectroscopy and photometry are re-analyzed using high-resolution spectra. The results of LTE and non-LTE model atmosphere analyses reveal general metal underabundances relative to solar values of typically 0.6 and…
Quasar H-beta profiles and discs.
Penston, M. V.; Perez, E.; Jackson, N.
We present high signal-to-noise spectra of the Hβ region of eight radio-loud quasars in an investigation seeking evidence for the emission of this line from a disc. Although we do not find the double-humped profile expected in simple versions of the disc hypothesis, we do find shoulders in the profile expected in a modified form of this idea. A mo…
SI II emission line diagnostics.
Judge, P. G.; Carpenter, K. G.; Harper, G. M.
The present study compares ratios of Si II UV emission lines in a variety of objects with computations based on recently published collisional data of Dufton and Kingston (1991). A high-quality spectrum of Alpha Tau (K5 III) obtained by Carpenter et al. (1991) is analyzed using the G270M mode of the GHRS on the HST, in addition to high-dispersion …
The SI II intercombination multiplet in late-type stars.
Dufton, P. L.; Keenan, F. P.; Byrne, P. B. +3 more
New atomic data are used to calculate the relative intensities of transitions within the Si II 3s(2)3p(2)P-3s3p(2) 4P intercombination multiplet for plasma parameters appropriate to late-type stellar atmospheres. These ratios are found to be significantly different from those of Dufton and Kingston, (1991), principally due to changes in the radiat…
IUE observations of the quasar 3C263 constrain the ionizing photon luminosity of decaying dark matter.
Fabian, A. C.; Naylor, T.; Sciama, D. W.
Dark matter which produces hydrogen-ionizing photons on a time-scale of 2x1023s has been shown by Sciama to explain many problems in astronomy and cosmology. Clusters of galaxies composed of such dark matter will be luminous sources of ionizing photons. The authors report here the results of a search for an otherwise unidentified, exten…
Ultraviolet observations of the long-period dwarf nova DX And in outburst.
Woods, J. A.; Drew, J. E.; Hoare, M. G.
Ultraviolet observations of the little-studied dwarf nova, DX And, are presented. The observations were made with the International Ultraviolet Explorer satellite during the late stages of a rise to outburst maximum in November 1989. The spectra indicate a low orbital inclination angle and show clear signs of substantial interstellar reddening. Th…
Ultraviolet emission-line variability in 3C273.
Harries, T. J.; O'Brien, P. T.
Evidence is presented for correlated variability between the ultraviolet continuum and the Lyα emission line in the luminous quasar 3C273. Using IUE data covering a period of ~ 1000 d, Lyα varied by 15 per cent whilst the continuum varied by a factor of 2. A time series analysis gives a lag for Lyα relative to the ultraviolet continuum of 74 +/- 3…
On the magnetic energy density in the X-ray emission of active galactic nuclei.
Ghisellini, G.; Fabian, A. C.; Celotti, A.
We estimate upper limits on the magnetic energy density in the compact X-ray emission region of the Seyfert galaxies NGC 4051 and NGC 6814 and the quasars 3C273, 3C279 and H1821 + 643 using synchrotron self-Compton theory. The size of the emission region is obtained from the X-ray variability time-scale, and the electron density from the assumptio…
The variable broad emission line spectrum of 4C 37.43.
Gondhalekar, P. M.; O'Brien, P. T.
The results of a short campaign to monitor the quasar 4C37.43 using the International Ultraviolet Explorer (IUE) satellite are presented. Combining these data with archive data we find clear evidence for ultraviolet continuum and Ly α emission line variability. Most of the Ly α variability occurs in the wings of the line. The C IV λ1549 line may v…