Search Publications
Ultraviolet and Visual Wavelength Spectroscopy of Gas around Eta Carinae
Davidson, K.; Gull, T. R.; Dufour, R. J. +1 more
Observational results of η Carinae are reported, especially spectroscopy of the outer 'S condensation' supplemented by data on the homunculus and its core. Theoretical calculations of atmosphere/wind models and of the shock-heated S condensation are needed for a proper analysis of the data, but some simplified results are discussed. The helium abu…
Cometary Grain Scattering versus Wavelength, or, ``What Color Is Comet Dust?''
Jewitt, David; Meech, Karen J.
Optical and near-infrared observations of comets are combined in a systematic study of the wavelength dependence of the scattering from cometary grains. The normalized rate of change of the reflectivity of cometary grains with respect to the wavelength of observations decreases as the wavelength increases. The observed wavelength dependence of the…
New Results on the X-Ray Emission and Its Correlation with the Ultraviolet in NGC 4151
Piro, L.; Perola, G. C.; Altamore, A. +8 more
Results from observations of the Seyfert galaxy NGC 4151 obtained with Exosat (0.1-25 keV) and IUE (1200-3000 A) during November 1983, and between December 1984 and January 1985, are presented. The stability of the flux during large-scale variations in the UV and X-ray regions suggests that the soft X-ray excess noted by Holt et al. (1980) represe…
Rotational period of comet Halley
Schleicher, D. G.; Millis, R. L.
The rotational period of the nucleus of comet Halley is a basic datum which must be accurately known if the vast collection of observations of this comet recently obtained from spacecraft and ground-based observatories are to be correctly interpreted. Sekanina and Larson, who have studied the morphology of the comet's coma, find a period near 2.2 …
Narrow Absorption Components and Variability in Ultraviolet P Cygni Profiles of Early-Type Stars
Howarth, I. D.; Prinja, R. K.
An extensive set of velocity and column density measurements of both narrow absorption components and 'underlying' P Cygni profiles is presented for a sample of 21 main-sequence, giant, and supergiant stars with spectral types B1-O4, selected as having at least one of the NV, Si IV, and CIV resonance doublets unsaturated. To study variability char…
The Giotto encounter with comet Halley
Reinhard, R.
The Giotto spacecraft encountered comet Halley on 14 March 1986, approaching to within ~600km of the nucleus. Its scientific payload comprised ten hardware experiments: a narrow-angle camera, three mass spectrometers (for neutrals, ions and dust), various dust detectors a photopolarimeter and a set of plasma experiments. All experiments performed …
Dwarf novae in outburst : modelling the observations.
Verbunt, F.; Pringle, J. E.; Wade, R. A.
Time-dependent accretion-disk models are constructed and used to calculate theoretical spectra in order to try and fit the ultraviolet and optical observations of outbursts of the two dwarf novae VW Hydri and CN Orionis. It is found that the behavior on the rise to outburst is the strongest discriminator between theoretical models. The mass-transf…
Spectroscopic Studies of Wolf-Rayet Stars. III. The WC Subclass
Conti, P. S.; Massey, P.; Torres, A. V.
Wolf-Rayet (W-R) stars, which are the descendants of massive O-type stars, can be subdivided into three groups depending on their spectral appearance. These groups include the nitrogen class (WN), the carbon class (WC), and the oxygen class (WO). The present paper is concerned with the WC stars. The assignment of WC subtypes has been based on visu…
The Evolution of Radiation-dominated Stars. I. Nonrotating Supermassive Stars
Woosley, S. E.; Fuller, G. M.; Weaver, T. A.
The evolution of nonrotating supermassive stars (M approximately equal to or greater than 5 x 10 to the 4th solar masses) is examined in detail using the results of hydrodynamic calculations which include post-Newtonian approximations to general relativistic gravity, an equation of state which includes electron-positron pairs, and all relevant nuc…
EXOSAT Observations of the 35 Day Cycle of Hercules X-1: Evidence for Neutron Star Precession
Pietsch, W.; Kahabka, P.; Truemper, J. +2 more
Her X-1 was observed with Exosat throughout a 35 day cycle at about 4 day sampling intervals. These measurements include, for the first time, an accurate determination of the 1.24 s pulse profiles during the short-on state at the middle of the 35 day cycle. The data show a large change in the pulse profiles between the main and short-on states, su…