Search Publications
Simultaneous multifrequency observations of the Seyfert 1 galaxy NGC 4051 : constant optical-infrared emission observed during large-amplitude X-ray variability.
Done, C.; Fabian, A. C.; Wamsteker, W. +5 more
We report simultaneous infrared, optical, ultraviolet and X-ray observations of the low-luminosity Seyfert 1 galaxy, NGC 4051. A new method of reduction was developed to correct the optical flux for atmospheric variations due to seeing and extinction. The X-ray flux varied by factors of up to 2 on time-scales of tens of minutes whilst the optical …
Fast spectroscopic variations on rapidly rotating, cool dwarfs III. Masses of circumstellar absorbing clouds on AB Doradus.
Penston, M. V.; Collier Cameron, A.; Ehrenfreund, P. +5 more
We present new time-resolved Hα, Ca II H and K and Mg II h and k spectra of the rapidly rotating KO dwarf star AB Doradus (= HD 36705). The transient absorption features seen in the Hα line are also present in the Ca II and Mg II resonance lines. New techniques are developed for measuring the average strength of the line absorption along lines-of-…
The variable X-ray absorption and soft X-ray excess of the QSO MR 2251-178.
Pounds, K. A.; Stewart, G. C.; Pan, H. C.
We present the results from a programme of 15 EXOSAT observations in which we monitored the QSO MR2251 - 178. Over the period 1983 October-1984 December the hard X-ray flux varied by a factor of 2. While there is an overall correlation between the ME(2-10 keV) and LE(0.1-2 keV) fluxes the pattern of variability is such that it cannot be described …
The ephemeris of X 1822-371.
Hellier, Coel; Mason, Keith O.; Smale, Alan P. +1 more
From the analysis of eclipses observed with the HEAO-1, Einstein, Exosat and Ginga satellites, it is shown that the orbital period of X1822 - 371 is increasing on a time-scale of 2.9 million yr. The period change, one of only three determined amongst the LMXBs, is in the opposite sense to the expected evolutionary trend, but in the same sense as t…
Localization of one of the galactic centre X-ray burst sources.
Skinner, G. K.; Eyles, C. J.; Foster, A. J. +1 more
Observations of an X-ray burst which occurred during the Spacelab-2 observations of the Galactic Center region are reported, and it is shown that it originated in the more southerly component of a previously reported persistent X-ray object, now resolved into two sources separated by 3 arcmin. Present knowledge of the number and location of the Ga…
Ultraviolet variability of NGC 4151 : a study using principal component analysis.
Penston, M. V.; Snijders, M. A. J.; Mittaz, J. P. D.
In an attempt at a decomposition of the different sources of variation in the spectra of NGC 4151, we have carried out a principal component analysis of spectra, seeking the number and form of the significant linearly independent spectra that are needed to reconstruct the data within the errors. Methods are outlined with particular emphasis on the…
The mass ratio of nu SGR from ultraviolet radial velocities.
Jeffery, C. S.; Dudley, R. E.
The first positive determination of the secondary orbit of the hydrogen-deficient binary υ Sgr has been achieved by the application of cross-correlation methods to high-resolution ultraviolet (UV) spectra obtained with IUE. The mass ratio thus obtained (q = 0.63±0.01) and the consequent minimum mass for the primary (Mp sin3i/…
Ultraviolet spectra of a large sample of quasars - II. Variability ofLy-alpha and C IV emission lines.
Gondhalekar, P. M.
The analysis of spectra of 34 quasars observed more than once with IUE is presented. The Lyα + N V and C IV emission lines in the spectra of some quasars in this sample change in intensity over a short time-scale. This time-scale is comparable to the time-scale for change observed in the intensity of emission lines in the spectra of low-luminosity…
Time dependence of the UV resonance lines in the cataclysmic variables SU UMa, RX And and 0623+71.
Verbunt, Frank; Drew, Janet E.; Woods, A. John
IUE observations of the dwarf novae SU UMa and RX And, and of the nova-like variable 0623 + 71 are presented. At the time of observation, SU UMa and RX And were in outburst. All three systems show variability in the wind-formed UV resonance lines of N V 1240 A, Si IV 1397 A and C IV 1549 A on timescales of hours. The amplitude of variation is smal…
Spectrophotometry of the shell around AG Carinae.
Dufour, Reginald J.; Mitra, P. Mila
Spatially-resolved long-slit spectrophotometry are presented for two regions of the shell nebula around the P-Cygni variable star AG Carinae. The spectra cover the 3700-6800 A wavelength range. Emission-line diagnostics are used to derive extinction, electron temperatures, and densities for various positions in the nebula. The chemical abundances …