Search Publications
Model atmospheres for Vega.
Castelli, F.; Kurucz, R. L.
We compared blanketed Local Thermodynamic Equilibrium (LTE) models for Vega computed both with the opacity distribution function (ODF) method and the opacity-sampling (OS) method. In the ODF case we used the ATLAS9 code with the new opacity data from Kurucz (1992). Model parameters for Vega depend on the amount of reddening and on the helium abund…
Interstellar oxygen, nitrogen and neon in the heliosphere
Geiss, J.; Galvin, A. B.; Mall, U. +3 more
Oxygen, nitrogen and neon pick-up ions of interstellar origin were detected for the first time with the Solar Wind Ion Spectrometer (SWICS) on board Ulysses. The interstellar origin of these ions is established by the following criteria: (a) they are singly charged, (b) they have the broad velocity distributions characteristic of pick-up ions, wit…
HST-GHRS observations of β Pictoris: additional evidence for infalling comets
Deleuil, M.; Feldman, P. D.; Moos, H. W. +9 more
Variable redshifted absorption features observed in the spectrum of β Pictoris have been attributed to comet-like bodies falling towards the star. The high quality data obtained in December 1992 at the unprecedented resolution and sensitivity of the GHRS reinforces the model that both the changes in spectral line shapes as well as the very presenc…
Spectral and correlated timing behaviour of GX5-1.
van Paradijs, J.; van der Klis, M.; Lewin, W. H. G. +4 more
We have analyzed the X-ray spectral and fast timing behaviour of the Z-source GX5-1 using X-ray colour-colour diagrams (CDs), hardness-intensity diagrams (HIDs) and power spectra. We used all EXOSAT ME data on GX5-1, a total of seven observations during 1983-1985. We detect, for the first time in GX5-1, secular motion of the well known "Z" pattern…
Is there primordial gas in IZw 18 ?
Kunth, D.; Sargent, W. L. W.; Lequeux, J. +1 more
The dwarf emission line galaxy IZw 18 has one of the lowest known O/H abundance ratios (O/H = 1.75 10^-5^) deduced from its emission lines. Its two main emission patches are associated with two extended HI clouds with very high column densities (N(HI) = 10^22^ H atoms cm^-2^). We have obtained spectra of the northwest emission region with the GHRS…
Temperatures and luminosities of symbiotic novae.
Murset, Urs; Nussbaumer, Harry
Symbiotic novae occur in double star systems, where mass lost by a red giant is accumulated by wind accretion onto a wite dwarf. When a critical mass has been reached, a nova-like outburst of long duration sets in, the outbursts lasts many dozons of years. We determine the evolution of luminosity and temperature during the outburst. We find slowly…
A study of the luminous blue variable candidate He 3-519 and its surrounding nebula.
Crowther, P. A.; Smith, L. J.; Prinja, R. K.
He 3-519 is 20 min away from the well-known Luminous Blue Variable (LBV) AG Car and is surrounded by a ring nebula 1 min diameter. In this paper, we present the first detailed study of He 3-519 and its surrounding nebula based on high resolution spectra obtained at the Anglo-Australian Telescope (AAT) with the University College London (UCL) echel…
GHRS observations of Sirius-A I. Interstellar clouds toward Sirius and Local Cloud ionization
Bertaux, J. L.; Ferlet, R.; Vidal-Madjar, A. +2 more
Echelle spectra of Sirius-A have been obtained with the Goddard High-Resolution Spectrograph (GHRS) on board the Hubble Space Telescope (HST). Interstellar absorption lines of iron and magnesium clearly show for the first time the presence of two distinct interstellar clouds between the Sun and Sirius at 2.7pc. Their projected heliocentric velocit…
Simultaneous observations of Seyfert 1 galaxies with IUE, ROSAT and GINGA
Walter, R.; Wamsteker, W.; Courvoisier, T. J. -L. +4 more
Simultaneous observations of 8 Seyfert 1 type active galactic nuclei (Fairall-9, Mrk 590, NGC 4051, 3C 273, NGC 5548, Mrk 841, Q1821+643 and 3C 390.3) obtained with IUE, ROSAT and, for 5 targets, with Ginga are presented and analysed with the aim to describe the ultraviolet to soft X-ray spectral component in these sources. The unobservable far ul…
Element abundances of classical novae.
Starrfield, S.; Drechsel, H.; Andrea, J.
Physical conditions and element abundances in the optically thin shells of 11 classical novae with outbursts between 1978 and 1989 were determined from an analysis of UV and optical spectra obtained during the nebular stage. Eight novae were studied on the basis of new optical and UV spectra: PW Vul (1984), QU Vul (1984), V842 Cen (1986), V827 Her…