Search Publications
HM Sagittae : the evolution of a symbiotic nova.
Vogel, M.; Nussbaumer, H.
HM Sge was discovered in 1975, when it became a symbiotic nova. HM Sge is still evolving. Since its discovery, significant spectral changes have taken place in the ultraviolet, the radio, as well as in the visual wavelength ranges. Here, IUE observations from 1982 to 1989 are reported. The implications of the available spectral information since t…
Observations of the new luminous blue variable R 110 of the Large Magellanic Cloud during an F star-phase.
Stahl, O.; Wolf, B.; Cassatella, A. +2 more
The LMC star R 110 has increased its visual brightness by about 0.5 mag in the last ten years. During its brightest observed phase in January and February 1989, we obtained UBVRI and JHK photometry, low dispersion spectroscopy with IUE, and high dispersion spectroscopy in the optical with CASPEC and in the satellite UV with IUE. During the brighte…
The Fe V/Fe VI ionization structure in WNE Wolf-Rayet winds.
Koenigsberger, G.
An analysis of the phase-dependent intensity variations of the Fe IV, V, and VI pseudocontinua in four WNE binary systems having different orbital separations is used to obtain information regarding the ionization and velocity structures of the wind of the WR component. The ratio of Fe VI/Fe V decreases in strength as a function of distance from t…
The UV spectrum as a signature of the lambda Bootis character.
Gerbaldi, M.; Faraggiana, R.; Boehm, C.
The spectra of all the stars previously classified as Lambda Bootis stars and observed by the IUE satellite at low resolution, in the short wavelength range, are analyzed. The usefulness of this spectral range for classifying the Lambda Boo stars is shown; the UV criteria used to distinguish the Lambda Boo stars from other metal-deficient stars ar…
The UV variability of BF Cygni.
Gonzalez-Riestra, R.; Cassatella, A.; Fernandez-Castro, T.
BF Cygni is one of the symbiotic systems in which orbital effects are better seen. The UV continuum and emission lines undergo large variations, in good agreement with the predictions of optical photometry. The strong changes in the shape of the ultraviolet continuum suggest the existence of a strongly wavelength dependent opacity. At least at som…
Lyman-alpha and MG II H and K fluxes in a sample of dwarf M stars.
Doyle, J. G.; Byrne, P. B.; Panagi, P.
Ly-alpha and Mg II fluxes are given for a group of M dwarfs. The Ly-alpha and Mg II lines were extracted from low resolution spectra taken with the IUE satellite. The Ly-alpha line is shown to be an important source of radiative losses in dMe chromospheres, being at least a factor of two more important than Mg II. Overall it contributes approximat…
The ultraviolet and X-ray spectrum of NGC 5548 : evidence for thermal Comptonization and geometrical variations.
Walter, R.; Courvoisier, T. J. -L.
Ultraviolet, soft and hard X-ray observations of NGC 5548 performed by IUE and EXOSAT give us a clear picture for the geometry of the emitting source. This picture is provided by the correlations observed between the large variations of the ultraviolet continuum, of the soft and hard X-ray fluxes, of the hard X-ray powerlaw index and of the equiva…
The variable ultraviolet absorption lines inthe Seyfert 1 galaxy NGC 3516.
Ulrich, M. H.; Walter, R.; Buson, L. M. +1 more
The ultraviolet spectrum of the Seyfert 1 galaxy NGC 3516 shows several intrinsic variable absorption lines. We analyze the properties of the CIV absorption profile, using IUE observations performed between 1978 and 1989. With certain assumptions which are supported by the observations and spelled out in the text, we are able to successfully model…
Rotational modulation and flares on RS Canum Venaticorum and BY Draconis-type stars. XIV. Phasen eclipse and flare observations of YY Geminorum by EXOSAT and IUE.
Schmitt, J. H. M. M.; Rodono, M.; Haisch, B. M. +1 more
The eclipsing spectroscopic binary YY Geminorum has been observed at optical, ultraviolet, and X-ray wavelengths for rotational modulation, eclipse variability, and flaring. The epoch T(phi = 0) = JD 2425698.3561, and the phase P = 0.81428224 d. The quiescent level of Mg II emission is remarkably steady during the three-year observing interval, wi…
An X-ray flare observed from van Biesbroeck 8.
Tagliaferri, G.; Doyle, J. G.; Giommi, P.
An X-ray flare was detected on the previously unknown flare-star van Biesbroeck 8 ( = Gl 644 C). The total energy of the event in the 0.05-2 keV energy range was 8 x 10 to the 31st erg/s with a mean luminosity of 1.8 x 10 to 28th erg/s. This implies an emission measure of about 6 x 10 to the 50th/cu cm, and adopting a simple loop model an electron…