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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…
Soft and hard X-ray variability from the accretion disk of NGC 5548.
Kaastra, J. S.; Barr, P.
EXOSAT observations of the Seyfert galaxy NGC 5548 confirm previous detections of a soft X-ray excess above a power law component. Both components show correlated variability on a typical time scale of half a day. There is evidence for a delay of the hard X-rays with respect to the soft X-rays of 1-2h. The spectral data can be explained in terms o…
Magnetic structure in cool stars. XVI. Emissions from the outer atmospheres of M-type dwarfs.
Mewe, R.; Rutten, R. G. M.; Schrijver, C. J. +2 more
Consideration is given to emission from the outer atmospheres of M-type dwarfs in several spectral lines originating from the chromosphere, the transition-region, and the soft X-ray emission from the corona. It is shown that M-type dwarfs systematically deviate from relations between flux densities in soft X-rays and chromospheric and transition-r…
The circumstellar gas around beta Pictoris. VIII. Evidence for a clumpy structure of the infalling gas.
Ferlet, R.; Vidal-Madjar, A.; Beust, H. +1 more
In a recent paper, the variable and redshifted circumstellar lines of ionized elements in the UV spectrum of Beta Pictoris were studied. The Al III doublet has been investigated, using both archival and recent IUE spectra of Beta Pic. This larger set of data is used to derive some general characteristics of the variable Al III lines. In particular…
High-Resolution Observations of Interstellar NA i and CA II Absorption Lines toward the Scorpius OB1 Association
Barlow, M. J.; Blades, J. C.; Crawford, I. A.
Observations of Na I and Ca II in absorption toward 22 stars in the Sco OB1 region, obtained at resolution R = 100,000 with a coude echelle spectrograph and 3.3-m camera on the 1.9-m telescope at Mt. Stromlo Observatory during 1986, are reported. The data are presented in extensive tables and graphs and analyzed in detail. Features discussed inclu…