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Wide-band X-ray observations of MK 501.
Ubertini, P.; Bazzano, A.; Brunner, H. +3 more
The BL Lacertae object MK 501 was observed by EXOSAT on 25 July 1984 for 3.65 hours. The data from the low energy (LE) and medium energy (ME) instruments suggest a single power law spectrum over the energy range 0.04 - 8 keV with a photon index of 2.5±0.1, an intensity at 1 keV of 0.022±0.003 photons/cm2s keV and a column density consis…
The historical record for Sirius: evidence for a white-dwarf thermonuclear runaway?
Sion, Edward M.; Kondo, Yoji; Bruhweiler, Frederick C.
Schlosser and Bergmann1 recently presented evidence that in medieval times Sirius was a bright red star, rather than the present bluish-white star, from which they have suggested that Sirius B is a recently born white dwarf. However, their model poses severe evolutionary problems. We present the results of our attempts to detect possibl…
A soft X-ray observation of ω Centauri with EXOSAT.
van Paradijs, J.; Jansen, F.; Verbunt, F. +2 more
In an observation with the LE1 CMA detector of the EXOSAT observatory the authors have detected two of the X-ray sources previously discovered in the globular cluster ω Cen with the IPC detector on board of the Einstein satellite. They give improved positions for these two sources. On the basis of comparison of the EXOSAT and Einstein count rates …
Rapid X-Ray and Optical Variability in the X-Ray--selected BL Lacertae Object 1E 1402.3+0416
Giommi, Paolo; Barr, Paul; Gioia, Isabella M. +4 more
Results from X-ray and optical observations of the X-ray-discovered BL Lac object 1E 1402.3 + 0416 are presented, where the X-ray measurements were carried out with the Channel Multiplier Array (CMA) and Medium Energy experiment (ME) detectors on board Exosat. These measurements revealed an intensity decrease by a factor of two on a time scale of …
The Unusual Ultraviolet Variability of the QSO 3C 232
Kafatos, M.; Bruhweiler, F. C.; Sofia, U. J.
After examining ultraviolet IUE spectra of 18 QSOs with z greater than 0.35, it is found that one object, 3C 232 (z = 0.533), stands out as exhibiting higly unusual spectral and continuum variability. The H I-Ly-alpha shows at a factor of two decrease in a day. The magnitude of the UV continuum variability is reminiscent of that seen in the optica…
HD 32918 : Ultraviolet spectrum and optical behaviour.
Grewing, M.; Bianchi, L.; Cassatella, A.
The first ultraviolet observations of HD 32918, a southern member of the FK Comae class, are presented. The observations were taken with the IUE satellite at two phases of the optical light curve, with simultaneous photometric coverage over more than one cycle in order to monitor the activity state of the star. The star shows very strong UV emissi…
The symbiotic star BX Monocerotis.
Altamore, A.; Rossi, C.; Friedjung, M. +4 more
The nature of BX Mon, a peculiar star characterized by a composite spectrum and very long period photometric variability, has been investigated. The star has been included in an extensive program of ESO observations of emission line stars. New results are discussed based on coordinated optical (IDS) and infrared observations made in February 1983,…
The MG II emission in a sample of regular-period RS CVn systems.
Fernandez-Figueroa, M. J.; de Castro, E.; Sedano, J. L.
The authors have studied a sample of ten RS CVn systems by means of IUE high resolution long wavelength spectra. A general trend toward decreasing chromospheric activity (Rhk) for slower rotating stars has been found. Considering the Rhk values and their relation with structural parameters (Teff, log g, log Pr…
A search for rotational modulation of the ultraviolet spectra of psi3 Piscium and 31 Comae Berenices.
Simon, T.
IUE observations were made daily over a 7 day interval to search for rotational variability in the ultraviolet emission lines of two rapidly rotating, early G giants, ψ3Psc and 31 Com. No evidence was found to suggest that the chromospheric and transition-region lines of these stars, or their ultraviolet continua near 1725 Å, are modula…
On the X-Ray and Ultraviolet Spectrum of the High-Redshift Quasar 3C 446
Tagliaferri, G.; Garilli, B.
Existing IUE and Einstein observations of the high-redshift (z = 1.414) quasar 3C 446 have been analyzed. In the UV the continuum is characterized by a steep slope. The lack of signal shortward of 2300 Å is probably due to the Lyman continuum absorption at the source. The X-ray spectrum shows the "universal" slope of active galactic nuclei coupled…