Search Publications
The discovery of a hot companion to the K-type supergiant HD 4817.
Cassatella, A.; Smolinski, J.
The discovery, through observations with the International Ultraviolet Explorer, of a B5 main sequence companion to the cool supergiant star HD 4817 (K2Ib-II) is reported. The object might be a new member of the Zeta Aur class. The UV observations indicate that HD 4817 is quite heavily reddened (E/B - V/ = 0.52) and that its distance is 1030 +/-80…
The soft X-ray variability of NGC 5548.
Kaastra, J. S.
The soft X-ray variability of NGC 5548 is studied using EXOSAT's low energy telescope in conjunction with the channel multiplyer array (CMA). For the first time, the pulse height distribution of the CMA data is used to infer information on the spectral variability. The spectrum of NGC 5548 consists of a hard power law and a soft component. During …
Variability in the noise properties of Cygnus X-1.
Belloni, T.; Hasinger, G.
The aperiodic variability in the X-ray emission of Cyg X-1 is examined from 13 Exosat observations covering the period July 1983 - October 1985, by means of broad band 0.001-100 H3 power spectra. The total rms fractional variations in the range 0.016-14 Hz is between 28 and 38 percent. The power distribution is flat below a characteristic break fr…
Observations of Cygnus X-2 with IUE : ultraviolet results from a multiwavelength campaign.
Raymond, J. C.; Hasinger, G.; Verbunt, F. +3 more
IUE observations of Cyg X-2 obtained during June and October 1988 are reported and analyzed, with reference to data from simultaneous X-ray and radio observations and the predictions of theoretical models. The results are presented in extensive tables and graphs and characterized in detail. The UV flux is shown to increase monotonically as the X-r…
An atlas of aperiodic variability in HMXB.
Belloni, T.; Hasinger, G.
From EXOSAT archive data of 14 X-ray binaries (12 high mass X-ray binaries and 2 low mass X-ray binaries) broad band power spectra and color- color diagrams are produced. The aperiodic (noise) variability of the sources is studied. All the X-ray pulsars present in the sample show strong noise components in the emission, with a fractional variabili…
X-ray emission from solar neighbourhood flare stars : a comprehensivesurvey of EXOSAT results.
Tagliaferri, G.; Stella, L.; Pallavicini, R.
Exosat Observatory observations of flare stars pertaining to 25 separate sources are examined. The Exosat instrumentation is described, and a data sample is presented. Quiescent and flaring emissions from UV Ceti-type flare stars as observed with a low-energy experiment on Exosat are discussed, and the results of the timing analysis of the low-ene…
Planetary nebulae with a high degree of ionization : NGC 2242 and NGC 4361.
Pena, M.; Torres-Peimbert, S.; Peimbert, M.
New observations in the 3400 - 7500 A range are presented for NGC 2242 and NGC 4361, and new IUE observations are presented for NGC 2242. The physical conditions and chemical composition for these nebulae are derived. The ionization structure of both PN are very similar, the PN are very optically thin to Lyman continuum photons, and more than 90 p…
Hot sublumous stars at high galactic latitudes. II. Physical parameters and distances of 37 sdB stars.
de Boer, K. S.; Heber, U.; Moehler, S.
Spectra and photometry of 37 subdwarf B stars mainly selected from Green et al. (1986), are analyzed to derive effective temperatures, surface gravities and helium abundances. Effective temperatures lie between 23,500 K and 32,000 K with values for log g between 4.5 and 5.6. The helium abundances vary between 0.03 and about 6 percent (number fract…
Multi-wavelength observations of 3C 273. II. 1986-1988.
Bouchet, P.; Falomo, R.; Walter, R. +9 more
Multi wavelength observations of 3C273 started in 1983. Since then data have been obtained from the radio end of the spectrum to the X-rays at more or less regular intervals. The sampling of the radio, near IR, visible and UV domains has greatly improved since 1985 and 1986, allowing useful cross-correlation analysis of the different components. A…
Abundances from B stars of the Magellanic Clouds.
Stahl, O.; Wolf, B.; Reitermann, A. +1 more
Model atmosphere analyses of two B giants, NGC 1818/D 12 and NGC 330/3, which are probably members of blue globular clusters of the LMC and SMC, respectively, are carried out. The analyses are based on CASPEC spectrograms (resolution ~20.000 S/N >/~ 50), on IUE low dispersion spectrograms (both SWP and LWP) and on UBVRI photometry. The analysis…