Search Publications
Multi-frequency variations of the Wolf-rayet system HD 193793 - I. Infrared, X-ray and radio observations.
van der Woerd, H.; van der Hucht, K. A.; Pollock, A. M. T. +3 more
Observations made of the Wolf-Rayet system HD 193793 over the 1979-1989 period in the radio, X-ray, and IR regions reveal great variations in all three regimes. The most complete coverage obtained was in the IR; attention is given to an IR outburst in 1985 during which the IR flux increased by as much as an order of magnitude over the course of se…
The ultra-compact broad emision line region in NGC 4151.
Perola, G. C.; Boksenberg, A.; Penston, M. V. +6 more
New observations of the UV continuum and emission lines of a Seyfert I galaxy are presented in which the time resolution is adequate to describe the character of variability. Using the IUE satellite, the nucleus of NGC 4151 was observed with a mean interval of 3.4 d during 2 months. The flux of the continuum and of most emission lines underwent la…
A model for the planetary nebula NGC 7027.
Middlemass, D.
Extensive photoionization modeling of NGC 7027 is presented using the most recent observations available. The effects of the differential extinction caused by the local dust cloud are considered and corrections are made to large-aperture line fluxes. Abundances are derived from a large number of collisionally excited and recombination emission lin…
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-…
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 …