Search Publications

The UV variability of BF Cygni.

Gonzalez-Riestra, R.; Cassatella, A.; Fernandez-Castro, T.

BF Cygni is one of the symbiotic systems in which orbital effects are better seen. The UV continuum and emission lines undergo large variations, in good agreement with the predictions of optical photometry. The strong changes in the shape of the ultraviolet continuum suggest the existence of a strongly wavelength dependent opacity. At least at som…

Ultraviolet Colors as Age Indicators for LMC Clusters

Freeman, K. C.; Meurer, Gerhardt R.; Cacciari, C.

Empirical correlations are found between log ages (logτ) intrinsic ultraviolet colors C(18 - 31)_0_ and C(25 - 31)_0_ for 27 LMC clusters, where log τ is on the uniform age scale of Elson correlations as age indicators for LMC clusters and other stellar populations are discussed. The results are partially based on a new calibration of log τ vs the…

IUE and Einstein Survey of Late-Type Giant and Supergiant Stars and the Dividing Line

Maggio, A.; Vaiana, G. S.; Haisch, Bernhard M. +2 more

Results are presented on an IUE UV survey of 255 late-type G, K, and M stars, complementing the Maggio et al. (1990) Einstein X-ray survey of 380 late-type stars. The large data sample of X-ray and UV detections make it possible to examine the activity relationship between the X-ray and the UV emissions. The results confirm previous finding of a t…

Lyman-alpha and MG II H and K fluxes in a sample of dwarf M stars.

Doyle, J. G.; Byrne, P. B.; Panagi, P.

Ly-alpha and Mg II fluxes are given for a group of M dwarfs. The Ly-alpha and Mg II lines were extracted from low resolution spectra taken with the IUE satellite. The Ly-alpha line is shown to be an important source of radiative losses in dMe chromospheres, being at least a factor of two more important than Mg II. Overall it contributes approximat…

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…