Search Publications
HZ Her: the nature and origin of the emission lines.
Howarth, I. D.; Wilson, B.
The line spectrum of HZ Her/Her X-1 is investigated in highand low-dispersion IUE spectroscopy. It is noted that while velocity considerations discredit the classical sites of mission, which are the primary star's X-ray heated photosphere, accretion stream, and disk, they support an origin in discrete blobs of material orbiting at the rim of the a…
IUE observations of X-ray selected Seyfert galaxies.
Willis, A. J.; Wilson, R.; Barr, P.
Results are presented for 1150-3150 A spectrophotometry of six type I Seyfert galaxies - NGC 5548, Markarian 79, Markarian 279, Markarian 506, Markarian 376, and 3C 390.3. It is found that the continuous flux distribution can be represented by a single power law in four of these objects, with spectral indices between + 0.2 and - 3.1, while NGC 554…
The conspicuous absence of normal graphite grains in the Small Magellanic Cloud.
Bromage, G. E.; Nandy, K.
The simplest dust model that accurately predicts the normal Galactic interstellar extinction, also fits the normal SMC curve derived from visible and IUE observations. Only one parameter value is different: the usual graphite contribution is at least a factor of 7 weaker in the SMC. Some possible explanations are discussed.
The old-nova GK Per (1901). III. Accretion disc models.
Bianchini, A.; Sabadin, F.
The UV spectrum of the old-nova GK Per (1901) at quiescence greatly differs from those of the other observed old-novae. In spite of the presence of high excitation emission lines, the UV to visual continuum energy distribution is peaked at ≡3600 Å, whereas for most old-novae it steeply rises towards shorter wavelengths. The authors have constructe…
Zinc as a tracer of metallicity in the interstellar medium.
Bromage, G. E.; Blades, J. C.; Harris, A. W.
The relative gas-phase abundance of zinc in the interstellar medium has been studied using high-resolution spectra from the IUE data bank of early-type stars with distances of up to 3 kpc. The chosen sight-lines all have measured N(H) values derived from Copernicus observations. Results show that in the H column density range of 5×1019 …
Models of the planetary nebulae IC 2003, NGC 3242, 6210 and 7009 : constraints on the ionizing radiation of the central star.
Koeppen, J.
Using ultraviolet, optical, and infrared emission line data, ionization models for four planetary nebulae are constructed. In the fitting procedure, we place emphasis on [O III] λ500.9 nm and [O III] λ436.3 nm to reproduce both the ionization and thermal balance in the O++ zone. The ratios C IV λ155.0 nm/C III] λ190.8 nm, N IV] λ148.7 n…
Ultraviolet spectroscopy of LSI +61 303.
Howarth, I. D.
New IUE low-resolution spectroscopy of the X-ray/radio source LSI+61°303 is presented and discussed, and previously reported data critically reassessed. There is no strong evidence for continuum variability; in particular, eight spectra covering the 1200-1950 Å region show a scatter of only ≡3 per cent. There is some variability in the emission li…
X-ray and UV observations of the BL Lacertae object 3C 66A.
Maccagni, D.; Maraschi, L.; Tanzi, E. G. +2 more
The energy distribution of the BL Lac object 3C 66A has been investigated in the soft X-ray range by means of repeated observations with the Einstein Observatory and in the UV range by means of the IUE satellite. The available optical photometry from 1979 to 1981 is reported. 3C 66A is characterized by violent X-ray activity over a time scale of 6…
Three low-redshift quasars with absorption systems: IUE andoptical observations.
Kunth, D.; Bergeron, J.
The authors have discovered the first two cases of narrow absorption systems with an absorption redshift equal to the emission redshift (Δv ⪉ 500 km s-1) in the low-redshift quasars PKS 1912-54 (zem = 0.401) and PKS 2135-14 (zem = 0.200). They also confirm the existence of a sharp absorption system (zab …
The circumstellar dust of MU Cephei.
Martin, P. G.; Rogers, C.; Crabtree, D. R.
An accurate solution to the equation of transfer in spherical geometry (including an anisotropic phase function) is used to model IUE observations of the circumstellar extinction of Mu Cep. Some grain materials can thus be eliminated from consideration while others can be restricted in grain size (and envelope optical depth). Further discriminatio…