Search Publications
The luminous quasar HS 1700+6416 and the shape of the "big bump" below 500 A.
Clavel, J.; Reimers, D.; Wamsteker, W. +5 more
In the course of the Hamburg quasar survey a bright (V = 16.1) high redshift (z = 2.72) quasar has been discovered. Follow-up optical high (0.4 A) and low (6 A) resolution spectrophotometry together with IUE observations are presented. With a luminosity at λ_rest_ = 1450 A, L_1450_ = 6 x 10^32^ erg s^-1^ Hz^-1^, HS1700+6416 is the second most lumi…
The flux and spectral variability of NGC 6814 as observed with EXOSAT.
Branduardi-Raymont, G.; Mittaz, J. P. D.
We present five EXOSAT observations of the Seyfert galaxy NGC 6814 which were carried out over the period 1983 September to 1985 October at intervals of a few months to a year. Over these time-scales the soft X-ray (0.02-2.5 keV) flux of NGC 6814 varies by large factors, decreasing by over and order of magnitude in the first 9 months; this is foun…
EXOSAT observations of the X-ray burst source 4U 1608-52.
van Paradijs, J.; Lewin, W. H. G.; Tan, J. +2 more
The results of an analysis of two Exosat observations (July 1984, May 1986) of the highly variable X-ray burst source 4U 1608-52 are presented. During both observations the persistent X-ray flux was low (quiescence), and the persistent X-ray spectrum could be well fitted with a power-law model, with approximately the same index, but a somewhat dif…
UV Fluorescence of Molecular Hydrogen and Red Dust Emission in the Gamma Cassiopeiae Nebulae IC 63
Bohlin, Ralph C.; Witt, Adolf N.; Stecher, Theodore P. +1 more
Resonant fluorescence of molecular hydrogen has been observed in the reflection nebula IC 63 with the IUE satellite. Both the noncoherent resonant scattering and the dissociative continuum are shown to agree well with molecular theory. Extended red emission is also found in this nebula and may be physically related to the dissociation of H2.
Ultraviolet observations of stellar winds in Be and 'normal' B non-supergiant stars.
Prinja, Raman K.
Model profile fits to high-resolution IUE C IV, Si IV, and Si III spectra are used to produce a homogeneous set of wind-velocity and column-density measurements for 40 early-type Be stars and 40 nonemission, nonsupergiant B stars. The mass-loss characteristics in the Be and normal B stars are compared. Results on stellar wind morphology, velocitie…
Non-LTE analysis of extremly helium-rich stars. I. The hot sdO stars LSE 153, 259 and 263.
Husfeld, D.; Butler, K.; Heber, U. +1 more
Results of a non-LTE fine analysis based mainly on high-resolution CASPEC spectra for three extremely helium-rich sdO stars are discussed in order to explain hydrogen deficiency in single stars. High temperature (Teff = 70,000 to 75,000 K) and a position in the log Teff - log g diagram were found close to the Eddington limit. Various abundance est…
Simultaneous X-Ray, Ultraviolet, and Optical Observations of the BL Lacertae Object PKS 2155-304
Maccagni, D.; Maraschi, L.; Tanzi, E. G. +6 more
X-ray observations of PKS 2155-304, performed at nine epochs in 1983-1985 with the EXOSAT satellite, are reported. The source was observed quasi-simultaneously in the far-UV with IUE, and in the optical and infrared with ESO telescopes. X-ray light curves with 400 s time resolution are derived. On two occasions the flux showed a rapid regular risi…
Two X-Ray--selected BL Lacertae Objects Observed with the HEAO 1 Scanning Modulation Collimator
Buckley, D. A. H.; Schwartz, D. A.; Tapia, S. +4 more
We have discovered two 16th magnitude BL Lac objects, H1101-232 and H1426+428, during an ongoing program to identify the optical counterparts of X-ray sources from the HEAO 1 survey. Each is a persistent and relatively bright X-ray source that was also detected by the Uhuru and Ariel 5 surveys. Our classifications are based on the combined observa…
On the Nature of the Symbiotic Star BF Cygni
Kenyon, S. J.; Mikolajewska, J.; Mikolajewski, M.
Optical and ultraviolet spectroscopy of the symbiotic binary BF Cyg obtained during 1979-1988 is discussed. This system consists of a low-mass M5 giant filling about 50 percent of its tidal volume and a hot, luminous compact object similar to the central star of a planetary nebula. The binary is embedded in an asymmetric nebula which includes a sm…
Coronal Activity in F-, G-, and K-Type Stars. IV. Evidence for Expanding Loop Geometries in Stellar Coronae
Mewe, R.; Schrijver, C. J.; Lemen, J. R.
A detailed analysis is presented of X-ray spectra of Capella and of Sigma2 CrB. The spectra of both stars are compatible with coronae consisting of two different ensembles of static loops with different maximum temperatures and ratios of the cross sectional areas at the loop top and at the footpoint. The cool (5 MK) loop components in both stars s…