Search Publications
HD 159176: photospheric and wind-dominated light-curve analyses coupled to wind modelling
Pachoulakis, Ioannis
HD 159176 is a hot, massive, non-eclipsing binary with a small-amplitude ellipsoidal variability. The existing velocity solution determines the ratio of the stellar masses. In the present article these radial velocities, coupled with one optical and two UV light curves derived from IUE images in bandpasses devoid of stellar wind lines, are solved …
The binary Cepheid W Sgr.
Cottrell, P. L.; Albrow, M. D.
High-resolution spectra have been obtained over a seven-year period for the 7.6 d binary Cepheid W Sgr. Radial velocities measured from these spectra have been combined with those measured with the CORAVEL radial velocity spectrometer and a new orbital solution obtained with the parameters P = 1603 d, K = 1.90 km s-1, e = 0.42. Velociti…
The origin of the correlation between the UV and X-rays in NGC 4151
Zdziarski, Andrzej A.; Magdziarz, Pawel
We propose that the UV/X-ray correlation observed in NGC 4151 by EXOSAT and IUE is due to re-emission of the X-ray flux absorbed by cold clouds in the line of sight. This transmission model satisfies the energy balance, provides a good fit to the X-ray and UV data, and predicts no Compton reflection of X-rays (as observed). Alternatively, the corr…
The narrow variable components of CIV in NGC 4151 from 1981 to 1987
Ulrich, M. -H.
The nucleus of the Seyfert 1 galaxy NGC 4151 undergoes large-amplitude variations and occasionally passes through deep minimum states lasting up to a few months. Two narrow emission lines, L_1 and L_2, variable in intensity on a time-scale of a few days were discovered during International Ultra-violet Explorer (IUE) campaigns at low states in 198…
Further optical and UV spectroscopy of stars in the direction of the Riegel & Crutcher cold cloud
Hambly, N. C.; Bates, B.; Kemp, S. N.
Further optical and UV spectral data are presented for four stars in the direction of the Riegel & Crutcher cold cloud. Two of the stars lie close in position to the area covered by our previous optical, UV and radio studies near l=10 deg, while the other two stars lie near l=15 deg. The stars range in distance from about 140 pc to 1.5 kpc. Th…
A paradigm revisited: the accretion disc in AGNs and quasars
Gondhalekar, P. M.; Kellett, B. J.; Rouillon-Foley, C.
A statistical comparison of model spectra of a thin bare accretion disc plus power-law and observations of over 400 active galactic nuclei (AGNs) and quasars are presented. This comparison is not limited to the optical/ultraviolet region of the observed spectra, as has often been the case in the past, but is extended over the entire ~4 eV to ~2 ke…
The UV O I triplet and H Lyman β pumping in the ζ Aurigae star HR 6902.
Marshall, K. P.
The radiative transfer code MULTI has been used, in conjunction with a model photosphere and chromosphere for the primary star of the ζ Aur system HR 6902, and a 14-level oxygen atomic model which incorporates up-to-date atomic data, to investigate the rôle of photoexcitation and hydrogen Lyman β pumping in the UV O I resonance triplet at 1302.168…