Search Publications
A study of ultraviolet spectra of dzeta Aurigae/VV Cephei systems. XI. 22 Vulpeculae : IUE observations of its extended chromosphere and wind with spatial resolution.
Reimers, D.; Schroeder, K. -P.
A set of 18 high resolution IUE spectra of chromospheric-eclipse phases of 22 Vulpeculae are analyzed by means of growth curves. A density model is presented and the upper limit of the electron density is determined. Si II UV mult. 2 wind resonance lines at several phases are modeled with a two-dimensional transfer code. It is found that although …
Intermediate resolution spectra of quasars with z>2.
Ulrich, M. -H.
20 quasars (optically selected) with redshifts in the range 2-2.7 have been observed with a spectral resolution of 7 A, for a statistical study of the properties of the emission lines and also to find interesting candidates for detailed studies. The distribution of the observed equivalent width (EW) of C IV is centered at 95 A and the distribution…
Properties of the components of the UZ Librae system.
Grewing, M.; Garrido, R.; Bianchi, L.
A reanalysis is conducted of the available photometric and spectroscopic data for the K-giant UZ Librae, including recent uvby photometry. The rotational period thus derived is close to, but not identical with the orbital period. Attention is given to UV spectra taken at different orbital/rotational phases. It is concluded that the overall propert…
Phase variations of 88 Herculis : do the UV observations confirm a connection between these variations and the changes of the phospheric parameters of the underlying star ?
Zorec, J.; Hoeflich, P.; Divan, L.
It is shown that the observed far-UV flux variation of 88 Herculis from 1976 to 1979 is lower than previously reported. The variation from 1979 to 1983 is difficult to confirm. The remaining flux changes cannot be attributed to changes in the stellar luminosity of the star. Furthermore, the constancies of the size and of the position-wavelength of…
Evidence for near-surface breezes on Comet P/Halley
Keller, H. U.; Thomas, N.
Halley Multicolor Camera (HMC) images taken of the nucleus of Comet P/Halley and its environment from on board ESA's spacecraft, Giotto, provide substantial evidence for flow of dust particles almost parallel to the surface at small cometocentric distances. This evidence is summarized and discussed with reference to other spacecraft experiments, g…
Stellar wind velocities and luminosities of O stars.
Stalio, R.; Bernabeu, G.; Magazzu, A.
Stellar wind velocities (v-edge not greater than v-infinity) for 110 O stars are calculated. The spectral types in the sample range from O3 through B0; all luminosity classes are represented. Stars from clusters and associations (extreme Population I) as well as field stars are considered. There is a weak evidence of higher v-edge for extreme Popu…
Rotational modulation and flares on RS Canum Venaticorum and BY Draconis stars. XII. Near-to-simultaneous high resolution UV and optical observations of II Pegasi during July 1984.
Doyle, J. G.; Byrne, P. B.; Marang, F. +4 more
Nearly simultaneous high resolution ground-based optical and IUE satellite UV spectroscopy and an optical light curve of the RS CVn star II Peg are presented. It is shown that the chromospheric and transition region radiative losses of the star in July 1984 are lower than previously recorded means. The flux in the Lyman-alpha line is estimated and…
An X-ray and optical study of the low-mass X-ray source 4U 1556-605.
Motch, C.; Beuermann, K.; Pakull, M. W. +1 more
Partly simultaneous EXOSAT and optical observations of the low-mass X-ray binary 4U 1556-605 are presented. X-ray flux variations of relatively small amplitude (about 20 percent) are accompanied by a significant hardening of the X-ray spectrum. This behavior is investigated in the framework of several currently proposed spectral models. The optica…
High resolution IUE observations of the flare star AD Leonis : implications for the MG II Wilson-Bappu effect.
Pettersen, B. R.; Ambruster, C. W.; Sundland, S. R.
The first high resolution IUE observations of the classical M dwarf flare star, AD Leonis is reported. For the Mg II h and k emission lines (2795 and 2803 A), no variation in the line strength, width, or flux is found in four spectra spanning 24 hr. The lines are broader in AD Leo than in AT Microscopii and AU Microscopii, the only other M dwarfs …
A study of the ultraviolet spectrum of VV Cephei.
Hack, M.; Engin, S.; Yilmaz, N.
The IUE images of the atmospheric eclipsing binary VV Cep (M 2 Ia e + B, P = 20.3 yr) were studied. The absorption and emission lines in the high-resolution spectra were identified. No interstellar absorption lines were detected despite the large degree of reddening. The comparison of the UV energy distribution of VV Cep after the end of the eclip…