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The rapidly oscillating AP stars as a test of stellar chromospheric heating mechanisms.
Sonneborn, G.; Shore, S. N.; Brown, D. N. +1 more
The discovery of a new class of magnetic stars, the rapidly pulsating Ap stars, provides an unprecedented tool for the study of Alfvénic heating in the outer atmospheres of main sequence stars. In this note, the authors point out that detection of rotationally modulated chromospheric emission line fluxes, especially the Ca II, Mg II, and C IV line…
X-ray and UV observations of omega Centauri with EXOSAT.
Koch-Miramond, L.; Auriere, M.
The globular cluster ω Cen has been observed on two occasions, 6 months apart, with the Channel Multiplier Array on board EXOSAT, in the energy band 0.02 keV - 2.5 keV. The aim of the present investigation is to study the diffuse emission as well as the point sources discovered in the X-ray range with the EINSTEIN satellite (Hartwick et al., 1982)…
A subdwarf's startling stellar wind.
Howarth, Ian D.
Selected observations of the subdwarf HD 128220B are presented to illustrate several remarkable properties of its stellar wind. The N V resonance doublet shows a typical P Cygni profile, but the C IV doublet shows a highly structured, strongly variable absorption profile with up to nine discrete velocity components present at any one time. Velocit…
Giotto Observations of Comet Halley Dust
Zarnecki, J. C.; McDonnell, J. A. M.; Chakaveh, S. C. +3 more
Measurements of the dust environment of Comet P/Halley by the dust experiments on the Giotto and Vega spacecraft are discussed, as well as some aspects of the dust modelling that was carried out before the spacecraft encounters with the comet. These data have highlighted certain shortcomings in the models. For example, significant fluxes of grains…
The Giotto mission to Comet Halley
Reinhard, R.
Studies of calcium emission stars. I. HD 158393, a giant star in a binary system.
Lloyd Evans, T.; Balona, L. A.; Fekel, Francis C.
HD 158393 is a giant star of spectral type late G or early K which has moderately strong Ca II H and K emission cores. UBVRIJHK photometry and IUE spectra reveal a companion of type F0 - F2, luminosity class IV or V. Radial velocity data yield an orbit with a period of 31 day. The K and F stars have nearly equal mass, with a minimum value of 1.7 M…
X-Ray Emission from Non-Magnetic Cataclysmic Variables
van der Woerd, H.
EXOSAT observations of a large sample of non-magnetic cataclysmic variables have led to the detection of VW Hyi and OY Car as strong soft X-ray sources during superoutburst. The spectral characteristics of the X-ray emission of these SU Uma systems are compared. It is proposed that both systems have, besides a cool, optically thick boundary layer,…
Line blanketed model atmospheres of Ap-stars. VI. HD 221568.
Muthsam, H.; Stepien, K.
Visual and UV spectroscopic observations of HD 221568 together with line blanketed model atmospheres show that the star has an effective temperature of 10300K if log g = 3.7 is assumed. The temperature may be lower by about 100K in the phase of reddest B-V. Models with variable chemical composition are not able to reproduce observed light variatio…
The Upstream Region Foreshock and Bow Shock Wave at Comet p/ Halley from Plasma Electron Measurements
Anderson, K. A.; Reme, H.; Korth, A. +7 more
We survey the plasma electron parameters from a distance 2.7 × 106 km from the comet nucleus to the bow shock wave at about 1.1 × 106 km and somewhat beyond. We describe the features of the electron foreshock lying outside the shock to a distance of about 230,000 km. It is a region of intense solar wind-comet plasma interacti…
A Simultaneous X-Ray and Optical Study of Tt-Arietis
Stecklum, B.; Toth, I.; Richter, G. A. +21 more
Prelimary results of an extended program of coordinated X-ray and optical observations of TT Ari are presented. The object was observed on August 21/22 1985 both in X-rays (EXOSAT) and optical range, about 100 days after the return to the active state. The first detailed simultaneous study of TT Ari in active state indicates the presence of strong…