Search Publications
Revised chemical models of ζ Oph based on HST data
Williams, D. A.; Wagenblast, R.
Hubble Space Telescope observations by Savage, Cardelli and Sofia (1992) and Cardelliet al. (1993) have led to improved gas phase abundances for many elements in the diffuse cloud towards the star ζ Oph. Most remarkably, it was found that oxygen is much more strongly depleted than previousCopernicus observations indicated. As a consequence, chemic…
Detection of langmuir solitons: implications for type III burst emission mechanisms at 2ω PE
Goldstein, M. L.; Stone, R. G.; Thejappa, G.
We present the experimental verification of existing theoretical models of emission mechanisms of solar type III bursts at the second harmonic of the plasma frequency, ωpe. This study is based on the detection of Langmuir and envelope solitons by the Ulysses spacecraft inside three type III burst source regions. We show that the oscilla…
UV Observations of the Symbiotic Star EG And
Pereira, Claudio Bastos
EG And is a S-type symbiotic star. Here is present UV observations made by IUE from 1978 to 1991. From these observations the electronic density and the electronic temperature were obtained. The size of He II emitting region was estimated as 7.3R⊙. Line and continuum variations confirm the binary nature of EG And.
Winds of Luminous OB Stars
Howarth, Ian D.; Prinja, Raman K.
We review the historical development of observations of mass loss from hot, luminous stars, and sketch the physical principles underlying the theory of radiatively-driven stellar winds. The theory makes predictions which are shown to be in general accord with the data. We summarize recent results, primarily from the IUE satellite, which demonstrat…
The Broad Emission Line Region in AGNs and Quasars: The Impact of Variability Studies
Gondhalekar, P. M.; O'Brien, P. T.; Goad, M. R.
Coordinated observations of variability of the continuum and the emission-line luminosities (reverberation mapping) in AGNs and quasars have fundamentally altered our understanding of the broad-line regions in active galaxies. The constraints these observations impose on the models of the BLRs have been demonstrated here by an attempt to model the…
Recent observations of the WR central star of the planetary nebula LMC-N66
Peña, Miriam; Maza, Jose; Peimbert, Manuel +2 more
The recent evolution of the central star of the planetary nebula LMC-N66 is presented. Before 1987, it showed a weak continuum with aTeff≥120 000 K andLbol≈25 000L⊙ and in a few years it developed strong WR features (P Cygni line profiles in N v at 124.0 nm and C IV at 155.0 nm, wide HeII emission, etc.) typical of…
UV survey of δ Scuti stars: Final results and open problems
Pasinetti Fracassini, Laura E.; Pastori, Livio
The results obtained from our IUE observations of some δ Scuti stars and in particular 71 Tau and 69 Tau are reviewed. 71 Tau is the second brightest X-ray source of the Hyades cluster; on the contrary 69 Tau, very similar to 71 Tau in the optical range, does not show X emissions. The complex and in somewhat controversial scenario obtained from th…
A multi-layered backpropagation artificial neural network algorithm for UV spectral classification
Gupta, Ranjan; Mukherjee, Soma; Bhattacharya, Ujjwal +2 more
In this paper we present an application of an artificial neural network model based on a multi-layered backpropagation algorithm for spectral classification of UV data from the International Ultraviolet Explorer (IUE) low dispersion spectra reference atlas. The model used is similar to that of von Hippel et al. (1994), and is found to reduce the c…
Hubble Space Telescope observations of Magellanic cloud planetary nebulae: Stellar winds
Vassiliadis, Emanuel
Narrow-band [OIII] 500.7 nm images and ultraviolet spectrophotometry are obtained for ≈20 planetary nebulae (PNe) in the Magellanic Clouds using the Hubble Space Telescope (HST). Four objects show P Cygni-like features in the ultraviolet HST data, and/or broad emission complexes near the HeII 468.6 nm and CIV 580.6 nm lines in ground-based spectra…
The case of the fastest stellar wind in central stars of planetary nebulae
Perinotto, Mario; Patriarchi, Patrizio
An exceptionally fast wind (8500 km/s) was suggested to occur in the central star of the planetary nebula K1-16, belonging to the class of the PG 1159 H-deficient pre-white dwarfs. To ascertain the reality of such a fast wind this star has been observed with the HST telescope using the GHRS in the zone of theCIV 155.0 nm doublet. The HST data and …