Search Publications
Elemental abundances for a sample of southern galactic planetary nebulae.
Barlow, M. J.; Kingsburgh, R. L.
We present spectrophotometric observations of a sample of 80 southern galactic planetary nebulae (PN), and derive elemental abundances for 68 objects, supplementing the optical observations with Uv data in 25 cases. We define Type I PN as those objects that have experienced envelope-burning conversion to nitrogen of dredged- up primary carbon. Suc…
Thick tori around active galactic nuclei: a comparison of model predictions with observations of the infrared continuum and silicate features.
Danese, L.; Granato, G. L.
The continuum expected from active galactic nuclei (AGN) surrounded by thick tori is compared to the data available for a sample of optically selected Seyfert 1 galaxies. The optical and near-IR nuclear fluxes have previously been derived for these objects, and hence the spectral energy distributions (SEDs) of their active nuclei can be analysed. …
Terminal velocities of Wolf-Rayet winds from infrared He I lines.
Williams, P. M.; Eenens, P. R. J.
We have observed 1- and 2- im spectra covering the He i 2s-2p triplet and singlet lines in a sample of Wolf-Rayet stars. Most of the He ilines have P Cygni profiles, which are fitted using the SEI (Sobolev with exact integration) method to derive terminal velocities. From our observations of 41 stars, the He i velocities are only about 70 per cent…
A preliminary analysis of the planetary nebula central star V477 Lyrae.
Pollacco, D. L.; Bell, S. A.
We present a preliminary analysis of V477 Lyr, the eclipsing central star of Abell 46. Medium-resolution spectroscopy has been obtained, providing radial-velocity measurements for both components for the first time. New V-band charge coupled devices (CCD) photometry has also been obtained and the first full light-curve analysis is presented. The s…
A ROSAT survey of hot DA white dwarfs in non-interacting binary systems.
Barstow, M. A.; Koester, D.; Holberg, J. B. +3 more
A number of new non-interacting binary systems comprising a white dwarf plus a normal stellar companion have been discovered by the ROSA T X-ray and EUV sky surveys. We discuss the identification of nine of these objects, determine the temperatures and gravities of the white dwarfs, and compare their atmospheric compositions with the population of…
The spectrum of the planetary nebula NGC 6572.
Feibelman, W. A.; Hyung, S.; Aller, L. H.
A detailed, high-spectral-resolution study of the spectrum of the planetary nebula NGC 6572 is made for the optical region 365 to 1005 nm, using the Hamilton echelle spectrograph of Lick Observatory, and for the ultraviolet (UV) spectral region 125 to 320 rIm with the high-dispersion mode of the International Ultraviolet Explorer (lUE) satellite. …
RE 1738+665: the hottest DA white dwarf detected by ROSAT.
Barstow, M. A.; Koester, D.; Sansom, A. E. +6 more
One of the most important results of the ROSAT all-sky X-ray and EUV surveys has been the discovery of a large number of previously uncatalogued white dwarfs. One of these, RE 1738+665, is found to be the hottest hydrogen-rich DA white dwarf detected, with a temperature of 88000 K and log g =7.8, lying significantly above the 70000-K observational…
The nature of the newly discovered DO white dwarf RE 0503-289.
Werner, K.; Barstow, M. A.; Holberg, J. B. +2 more
We report the discovery of a hot DO white dwarf, RE 0503 - 289, which lies in a region of very low interstellar H I density. It lies within 1 deg of the hot DA white dwarf RE 0457 - 281 which we have reported as having the lowest directly measured H I column. A follow-up observation made using the Voyager 2 UV spectrometer reveals a strong continu…
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…