MAGNETICALLY CONTROLLED CIRCUMSTELLAR MATTER IN THE HELIUM-STRONG STARS

This paper reports the observation and interpretation of the ultraviolet spectrum variations of nine heliumstrong stars: HD 36485, 37017, 37479, 37776, 58260, 60344, 64740, 96446, and 133518. A unified model is developed to account for the observed correlation among three stellar properties: the line profile characteristics of the C IV and Si IV resonance doublets, the variations in the strength of these lines, and the inferred magnetic field geometry. We propose that circumstellar plasma is trapped in the stellar magnetosphere near the magnetic equator or is channeled to form jetlike outflows from the magnetic polar regions. These results, together with those of our previous study of the helium-weak sn stars, show that both helium-weak and helium-strong stars can possess magnetospherically trapped plasma, notwithstanding their different photo-spheric properties. We also present new results for radii and temperatures of the helium-strong stars in Ori OB 1 and for HD 64740 from low-dispersion IUE spectra.