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In-situ observations of a bi-modal ion distribution in the outer coma of comet P/Halley
Thomsen, M. F.; Wilken, B.; Feldman, W. C. +2 more
Observations obtained by the Johnstone Plasma Analyzer on the Giotto fly-by of comet Halley showed a fairly sudden decrease in the count rate of energetic (≡30 keV) water-group ions inside about 5×105km from the nucleus. This decrease was accompanied by the appearance of a new water-group ion population at slightly lower energies (<1…
A 25 min modulation from the vicinity of the unusually soft X-ray source X 0142+614.
White, N. E.; Branduardi-Raymont, G.; Giommi, P. +5 more
The results of three Exosat observations of X0142+614 made in August 1984 and November and December 1985 are reported. A 25-min coherent modulation was detected during the first observation, but not during the following two. The modulation peak-to-peak amplitude was 55 percent between 3 and 8 keV and less than 1 percent between 1 and 3 keV. The 1-…
Waves in the magnetic field and solar wind flow outside the bow shock at comet P/Halley
Johnstone, A.; Glassmeier, K.; Acuna, M. +2 more
The existence of hydromagnetic waves in the mass-loaded solar wind upstream from the bow shock of a comet is well-established both for comet Giacobini-Zinner and for comet Halley. Whereas previous reports have been concerned either with the magnetic field observations or with plasma observations, here the authors combine observations of the magnet…
Solar Wind Flow Through the Comet p/ Halley Bow Shock
Coates, A. J.; Winningham, J. D.; Thomsen, M. F. +7 more
The bow shock of a comet is formed by the interaction of three different particle populations; solar wind ions, cometary ions and electrons. We follow the behaviour of the solar wind protons through the Giotto inbound shock crossing at comet P/Halley. A foreshock boundary is seen at ∼1.4 106 km where the level of solar wind fluctuations…
Chromospheric MG II H and K emissions free of interstellar contamination : velocity structure in late-type dwarfs and giants.
Molaro, P.; Beckman, J. E.; Foing, B. H. +3 more
The authors have used high resolution IUE spectra from their own studies and from the archive to examine the Mg II h and k chromospheric emission cores of a sample of late-type dwarfs and giants. Sharp photospheric absorptions were used to provide a velocity rest-frame with respect to each stellar photosphere with the IUE-limited precision of ±4 k…
Studies of Hot B Subdwarfs. V. Continuing Investigation of the C, N, and SI Abundance Patterns in the Atmospheres of sdB Stars
Fontaine, G.; Wesemael, F.; Lamontagne, R.
High-dispersion ultraviolet observations of two hot, hydrogen-rich subdwarfs have been obtained with the IUE observatory and are presented. These data are analyzed with model atmosphere techniques, and element abundances for C, N, and Si are derived. Both PG 0342 + 026 (Te = 21,800 K) and PG 1104 + 243 (Te = 27,200 K) display abundances of these i…
A comparison of coronal X-ray emission observed with the Einstein andEXOSAT observatories.
Schmitt, J. H. M. M.; Monsignori-Fossi, B. C.; Pallavicini, R. +1 more
The present Einstein and Exosat observatories' star coronal X-ray emission data are subjected to a spectral analysis which employs the Raymond and Smith (1977) and Landini and Fossi (1984) computer codes to calculate X-ray emission from optically thin plasmas that are in collisional equilibrium. It is found that the derived coronal parameters depe…
Implications of the UV observations of SN 1987A.
Panagia, N.; Fransson, C.; Grewing, M. +2 more
The implications of the UV observations of SN 1987A are discussed. The authors conclude that the UV spectrum is not a distinguishing feature between Type I and II supernovae. There is therefore no contradiction with the optical observations. Instead it is proposed that the differences in the UV properties are to be sought in the varying degree of …
Multi-frequency observations of the 1985 outburst of RS ophiuchi
Snijders, M. A. J.
The 1985 outburst of the bright, recurrent nova RS Oph was almost simultaneously observed at X-ray, UV, optical, IR and radio frequencies at many epochs. The abundances in the ejected shell and the development of the bolometric luminosity as a function of time suggest that the cause of the outburst is a nuclear runaway on a massive white dwarf.
An activity-rotation relationship in F-M dwarfs from MG II H and K flux.
Doyle, J. G.
Mg II h and k fluxes are given for late-type dwarfs whose rotation periods are known. A good correlation between an activity parameter Rhk (represented by the ratio of Mg II h and k luminosity to bolometric luminosity) versus the Rossby-number is found for main-sequence stars F to late M. Both single and binary stars are found to follow…