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ROSAT/XRT-PSPC observations and the ionizing continuum of Seyfert 1 galaxy MKN 478
Gondhalekar, P. M.; Kellett, B. J.; Matthews, L. +2 more
The ROSAT/XRT-PSPC observations of the Seyfert 1 galaxy Mrk 478 are presented. Together with the optical and ultraviolet spectra of this galaxy, obtained within 8 months of the X-ray observations, these new data are used to determine the continuum energy distribution (CED) of Mrk 478, from 1 micron to about 2.0 keV with a small break between 11.3 …
He II lines from cataclysmic variable winds.
Hoare, M. G.
We present the first quantitative examination of the contribution of the stellar winds in high accretion rate, non-magnetic cataclysmic variables to the He II λ1640 and λ4686 lines. The line profiles are simulated with the Sobolev approximation using level populations taken from previous NLTE calculations which matched the observed strengths of th…
Extreme-ultraviolet spectrophotometry of HD 15638 and HR 8210 (IK Peg).
Barstow, M. A.; Koester, D.; Holberg, J. B.
The main-sequence stars HR 8210 (1K Peg) and HD 15638 have both been found to have DA white dwarf companions by observations with the lUE satellite, following their discovery as bright EUV sources by the ROSA T Wide Field Camera. Accurate estimates of the temperature and surface gravity of each white dwarf, based on the lUE data, were oniy possibl…
A new hot DA white dwarf in a region of exceptionally low HI density.
Kepler, S. O.; Fontaine, G.; Barstow, M. A. +11 more
We report the discovery of the hot DA white dwarf RE 0457-281 which has the lowest line-of-sight neutral hydrogen column density yet measured. The star was found independently by the ROSAT EUV, Montreal-Cambridge-Tololo and Edinburgh-Cape surveys. With an effective temperature of 60700 K and very soft EUV spectrum, this white dwarf resembles the w…
Multifrequency monitoring of the Seyfert 1 galaxy NGC 4593 - I. Isolating the nuclear emission.
Glass, I. S.; Clavel, J.; Peterson, B. M. +4 more
We present data obtained within a Campaign to monitor spectral variations in the low-luminosity Seyfert 1 galaxy NGC 4593, at X-ray, ultraviolet, optical and near-IR (J, H, K and L) frequencies. The different `parasitic' contributions that contaminate the pure nuclear continuous emission have been isolated and modelled. The light from the composit…
Hysteresis in broad-line regions of active galactic nuclei.
van Groningen, E.; Wanders, I.; Perry, J. J.
The response of emission-line luminosities to changes in the observed continuum in active galaxies is commonly used for reverberation mapping (RM) of the emission-line region. The method assumes regularity in the continuum source and linearity in the line response to the continuum, and that the phase-space distribution of the line-emitting gas is …
Time variability in the UV resonance lines of the cataclysmic variables MU Cen, AH HER and QU Car.
Knigge, C.; Drew, J. E.; Hoare, M. G. +1 more
We present a time-variability study of the uV resonance lines Nv 1240, Si iv 1397 and C iv 1549 in the dwarf novae AH Her and MU Cen and the nova-like variable QU Car. The main findings are as follows. (i)Virtually no variation can be seen in our data for MU Cen. (ii) AH Her shows velocity shifting of its resonance lines, with semi-amplitudes rang…
Ultraviolet and Radio Observations of the Young Rapidly Rotating k0 Dwarf Star HD197890
Carpenter, K. G.; Robinson, R. D.; Slee, O. B. +2 more
We present the results of UV observations taken with the International Ultraviolet Explorer (IUE) satellite and microwave observations obtained with the Australia Telescope during an observing campaign of the rapidly rotating K0 dwarf star III) 197890, nicknamed `Speedy Mic'. This star was recently recognized as a powerful, transient EUV source by…
Detection of episodic mass outflow in the newly discovered hot DO white dwarf RE 0503-289.
Barstow, M. A.; Sion, E. M.
We report the unexpected detection of variable mass outflow from the very hot (Teff =70000 K), He-rich DOZ1 degenerate RE 0503-289. This detection is based upon our analysis of absorption-line core strength variations and blueward asymmetries in two lUE echelle high-dispersion images obtained 13 months apart. The oufflow has a terminal velocity of…
Classification of the HIPPARCOS Input Catalogue Using the Kohonen Network
Hernandez-Pajares, M.; Floris, J.
The unsupervised classification with respect to stellar populations of 106 000 of the 118 000 Hipparcos input catalogue stars is presented, in terms of angular position and velocity, apparent magnitude and spectral type. The classification is performed first by merging the real data with a small sample of synthetic stars, which are representative …