Search Publications
The Ly-alpha and C IV lines in 10 low-redshift active galactic nuclei/quasars.
Buson, L. M.; Ulrich, M. -H.
We analyze the properties of the Ly α and C IV lines in 10 active galaxy nuclei/quasars with z < 0.2, for which relatively high quality spectra can be found in the first installment of the IUE "Uniform Low Dispersion Archives". A simple profile fitting of Ly α and of C IV with 2 gaussian components of different widths leads to the following res…
Simultaneous observations of the symbiotic star BF Cygni.
Gonzalez-Riestra, R.; Cassatella, A.; Fernandez-Castro, T. +1 more
Simultaneous ultraviolet/optical spectrophotometry and infrared photometry for the low excitation symbiotic star BF Cygni are presented. The analysis of the data suggests that three different components are present in the UV to IR energy distribution. A hot subdwarf with R = 0.48 solar radius and T not less than 60,000 K if the distance is 2.3 kpc…
Constraints on the inner accretion flow of 4U /MXB 1636-53 (V 801 Arae) from a comparison of X-ray burst and persistent emission.
van Paradijs, J.; Wijers, R. A. M. J.; Lewin, W. H. G. +4 more
A detailed analysis is presented of the importance of Comptonization in burst and persistent spectra of the low-mass X-ray binary 4U/MXB 1636-53, and from this analysis it is inferred that the inner accretion flow is geometrically thin. It is found that burst spectra of 1636-53 are very nearly Planckian in shape; from an upper limit to a high-ener…
The bimodal spectral and QPO-behaviour of GX 17+2.
Hasinger, G.; Truemper, J.; Langmeier, A.
The spectral and temporal analysis of Exosat observations of the bright galactic bulge source GX 17+2 is presented. The source shows a bimodal spectral and temporal behavior. High-frequency (24-28 Hz) quasi-periodic oscillations (QPO) are found on the horizontal branch of the H-I-diagram. There is evidence for a second harmonic at 50 Hz. QPOs with…
EXOSAT observations of three DA white dwarfs.
Beuermann, K.; Giommi, P.; Koester, D. +3 more
Exosat broad band filter observations, optical and IUE spectra, are presented for three DA white dwarfs. One source is a previously known Hyades white dwarf, the other two are new DA detected by Exosat. The results are consistent with previous observations of other DA white dwarfs and indicate that an absorber other than hydrogen (most probably he…
IUE observations of GL 644 AB (=Wolf 630) in the wavelength region 1150-1950 A, in June 1981.
Doyle, J. G.; Mathioudakis, M.
IUE short wavelength observations of the flare star Gl 644, obtained in June 1981 are presented. A flare was detected in one of the spectra as a strong increase in C IV, He II, and continuum fluxes. The electron density of the flaring plasma, determined using line ratio techniques, is 4 x 10 to the 10th/cu cm, which is an increase by a factor of 2…
Deviation from the Wilson-Bappu relationship in faint red dwarf stars.
Carlsson, M.; Engvold, O.; Elgaroy, O.
New observations of the Mg II h and k lines on red dwarf stars have been carried out with the International Ultraviolet Explorer observatory. It is found that several of the dwarf stars in the sample have Mg II h and k lines which are narrower than expected from the Wilson-Bappu relationship, that is established for stars brighter than M(v) about …
Activity in late-type stars. VI. Optical photometry and UV spectroscopy of the active dMe star, FK Aquarii in late 1983.
Lyons, M. A.; Butler, C. J.; Byrne, P. B.
Optical photometry and UV spectroscopy are reported for the flare/BY Dra star FK Aqr from 1983. These data are used to derive the rate of optical energy release in U-band flaring and compare it to four previous epochs. No conclusive evidence of any variation in this rate over an 8-yr interval has been found. No measurable BY Dra variations were pr…
WW Horologii : revised period and X-ray light curve.
Tagliaferri, G.; Beuermann, K.; Giommi, P. +2 more
An improved orbital period of the eclipsing AM Herculis binary WW Hor is reported, which allows the relative phasing of 1983 EXOSAT X-ray and the 1986-89 optical light curves to be established. It is found that X-rays and optical cyclotron continuum are produced by the same accreting pole on the magnetic white dwarf. In 1984, WW Hor was not detect…
The ultraviolet spectrum of solar analogs.
Altamore, A.; Rossi, C.; Rossi, L. +1 more
The ultraviolet high resolution IUE spectrum between 2600 and 3200 A of a sample of stars classified as solar analogs by Hardorp (1982 and references therein), including the southern solar twin HR 2290, is studied. A list of Fe II absorption line identifications and equivalent widths in the considered spectral region is presented. An analysis of t…