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The ultraviolet and X-ray spectrum of NGC 5548 : evidence for thermal Comptonization and geometrical variations.
Walter, R.; Courvoisier, T. J. -L.
Ultraviolet, soft and hard X-ray observations of NGC 5548 performed by IUE and EXOSAT give us a clear picture for the geometry of the emitting source. This picture is provided by the correlations observed between the large variations of the ultraviolet continuum, of the soft and hard X-ray fluxes, of the hard X-ray powerlaw index and of the equiva…
Studies of H i and D i in the Local Interstellar Medium
Moos, H. W.; Murthy, J.; Linsky, J. L. +3 more
High-dispersion IUE spectra are presented of the hydrogen Ly-alpha chromospheric emission line of two nearby late-type stars, Capella and Lambda And. Both interstellar H I and D I Ly-alpha absorption can be seen against the chromospheric line, and the density, velocity dispersion, and bulk velocity of the gas in those lines of sight are derived. L…
High-Latitude SPOT and Plage Activity on the Rapidly Rotating M Dwarf Star Gliese 890
Young, Arthur; Skumanich, Andrew; MacGregor, Keith B. +1 more
Simultaneous time-resolved observations in broadband photometry and in H-alpha and near-UV spectroscopy are presented of Gliese 890, a single M dwarf of the BY Draconis type with the shortest known period of rotation among field stars of its type. The continuum light curves exhibit modulations characteristic of the presence of localized dark spot …
The variable ultraviolet absorption lines inthe Seyfert 1 galaxy NGC 3516.
Ulrich, M. H.; Walter, R.; Buson, L. M. +1 more
The ultraviolet spectrum of the Seyfert 1 galaxy NGC 3516 shows several intrinsic variable absorption lines. We analyze the properties of the CIV absorption profile, using IUE observations performed between 1978 and 1989. With certain assumptions which are supported by the observations and spelled out in the text, we are able to successfully model…
The Discovery of Strong Neutral Atomic Carbon Absorption Lines in the Spectrum of the DAQZ5 White Dwarf in the Ultra--Short-Period Dwarf Nova WZ Sagittae during Quiescence
Szkody, Paula; Sion, Edward M.; Leckenby, Henry J.
X-ray spectral variations in NGC 4151.
Perola, G. C.; Fiore, F.; Romano, M.
In their analysis of the EXOSAT ME data on the Seyfert NGC 4151, Yaqoob, Warwick & Pounds found that the observed tendency of the spectrum to soften as the X-ray flux increases is due to variations in the absorbing column, which are anti-correlated with the source intensity, thus favouring a 'warm absorber' model. In this paper a re-analysis o…
Rotational modulation and flares on RS Canum Venaticorum and BY Draconis-type stars. XIV. Phasen eclipse and flare observations of YY Geminorum by EXOSAT and IUE.
Schmitt, J. H. M. M.; Rodono, M.; Haisch, B. M. +1 more
The eclipsing spectroscopic binary YY Geminorum has been observed at optical, ultraviolet, and X-ray wavelengths for rotational modulation, eclipse variability, and flaring. The epoch T(phi = 0) = JD 2425698.3561, and the phase P = 0.81428224 d. The quiescent level of Mg II emission is remarkably steady during the three-year observing interval, wi…
An X-ray flare observed from van Biesbroeck 8.
Tagliaferri, G.; Doyle, J. G.; Giommi, P.
An X-ray flare was detected on the previously unknown flare-star van Biesbroeck 8 ( = Gl 644 C). The total energy of the event in the 0.05-2 keV energy range was 8 x 10 to the 31st erg/s with a mean luminosity of 1.8 x 10 to 28th erg/s. This implies an emission measure of about 6 x 10 to the 50th/cu cm, and adopting a simple loop model an electron…
Interpretation of the inner coma observations of comet P/Halley by the Halley Multicolour Camera.
Keller, H. U.; Thomas, N.
The brightness dependence with distance of the inner coma of comet P/Halley, as observed by the Halley Multicolour Camera on board Giotto, shows 3 distinct regions. From about 400 - 2000 km from the nucleus, deviations from a z-1 law are evident where z is the distance from the nucleus centre. Fountain model calculations indicate that s…
Coronal X-ray emission from the short-period eclipsing binary XY UMa.
Jeffries, R. D.; Bedford, D. K.; Vilhu, O. +1 more
XY UMa, a close binary showing photospheric and chromospheric activity, has been observed with Exosat through 1.26 orbital cycles, with supporting optical photometry. The G2-5 V primary star is found to be responsible for the observed soft X-ray flux, which shows a clear primary eclipse. The X-ray-emitting coronal plasma is modeled to have two com…