Search Publications
The nature of the X-ray spectrum of VW Hydri.
Verbunt, Frank; van Teeseling, Andre; Heise, John
We analyze the EXOSAT data of the October 1984 superoutburst of the dwarf nova VW Hydri. We use the upper limit to the flux at 650 A, measured by VOYAGER, to argue that the spectral component that dominates at 1000 A does not significantly contribute to the counts in any of the EXOSAT filters. This is confirmed by analysis of a flux-ratio diagram,…
Activity in late-type stars. VIII. The nature of the dM(e) or "zero" H-alpha stars.
Byrne, P. B.
We present the results of ultraviolet spectroscopy of three M dwarf stars which, according to Stauffer & Hartmann (1986), have no Hα, either in absorption or emission, in their visible spectra. Using chromospheric and transition region emission line fluxes derived from these spectra, we demonstrate that these stars undergo lower rates of chrom…
HIPPARCOS link with Carte du Ciel triple images.
Tucholke, H. -J.; Brosche, P.; Guibert, J. +3 more
This study for the first time investigates the possibility of deriving astrometric positions for bright stars on Carte du Ciel (CdC) plates, whose triple images are not separable. The field from the Bonn Hipparcos Extragalactic Link Programme with the BL Lac object OJ 287 has been selected. The triple images on the CdC plate were modelled by three…
IUE observations of X-ray nova MUSCAE 1991 during outburst.
Shrader, C. R.; Gonzalez-Riestra, R.
We report on a series of ultraviolet spectroscopic observations made with the lUE satellite, which sampled critical outburst stages of the soft X-ray transient Nova Muscae 1991. Continuum light curves, and multi-epoch line analysis are presented. The λλ1500-3300 continuum fits approximately the "canonical" fv∝ν1/3 power law e…
Studies of narrow polar rings around E galaxies. II. The UV spectrum of AM 2020-504.
Buson, Lucio; Arnaboldi, Magda; Longo, Giuseppe +2 more
Four ultraviolet (UV) full-shift spectra secured with the IUE satellite have been used to test the accretion scenario for the still unexplored class of the "narrow" polar ring (PR) galaxies. The UV energy distribution in the λλ 1200 - 3300 A range for the "prototype" of this class, the system AM 2020-504, is found to be different from the UV emiss…
Imaging and spectroscopy of Abell 63 (UU Sge).
Pottasch, S. R.; Walsh, J. R.; Walton, N. A.
UU Sge, the eclipsing binary central star of the low- surface-brightness planetary nebula (PN) Abell 63, has been observed spectroscopically in the visible throughout its 11.2 hour period and especially during the minimum. A determination of the spectral types of the components of the binary system has been made. The primary hot central star is an…
An extended correlation between the Balmer and soft X-ray emission from solar and stellar flares.
Butler, C. J.
The integrated soft X-ray (8-12 Å) fluxes for solar flares, given by Thomas & Teske (1971), have been scaled to the equivalent EXOSAT (0.04-2.0 keV) fluxes using spectra obtained from a variety of rocket-based experiments and a model by Mewe for a 1.5 keV plasma. The data show good agreement with the soft X-ray-Hγ correlation established earli…
The spectral variability of the gamma-ray emission from Geminga and VELA and its implications.
Grenier, I. A.; Hermsen, W.; Henriksen, R. N.
The gamma-ray emissions from Geminga and from the Interpeak 1 component of the Vela pulsar were analyzed in order to compare their spectral properties between 50 MeV and 5 GeV and to study their variability between 1975 and 1982 using the COS-B data. The stability of both sources above about 200 and 300 MeV, respectively, retaining an E exp -2.0 +…
Variability and emission mechanism in Seyfert 1 galaxies : a near-infrared outburst in NGC 4051.
Hunt, L. K.; Del Zanna, G.; Wamsteker, W. +6 more
In the course of a 2.2 micron monitoring programme of nearby Seyfert 1 galaxies, we have detected an outburst in NGC 4051 in which the source flared and dimmed by more than a factor of 2 in 6 months. The UV flux, although sparsely sampled, is less variable than the near infrared. The available data suggest that dust reprocessing of the UV radiatio…
ROSAT-pointed observations of two gamma-ray burst error boxes.
Hurley, K.; Motch, C.; Kouveliotou, C. +3 more
We present ROSAT observations of two gamma-ray burst error boxes and of one possible optical transient source. No point sources were detected and a comparison is made with previous observations of the same objects (Boer et al. 1988, 1991). We interpret the data in the context of gamma-ray burst models that invoke galactic neutron stars. Although r…