Upper limits to coronal line emission from X-ray detected T Tauri stars.

Abstract

High dispersion AAT spectrograms of the two T Tauri stars, GW Orionis and T Tauri, are used to set upper limits to the intensities of the coronal emission forbidden line of Fe XIV at 5303 A. Comparison made with the intensities of chromospheric and the transition-region emission lines, and of the X-ray flux, shows that in GW Ori the Fe XIV forbidden line is fainter than might have been expected by comparison with the sun. Overall differences in temperature structure in the wind regions of the different stars are apparent. For example, in RU Lupi, the corona is very weak compared to the chromosphere and transition region. A crude model is fitted to the emission measures, giving the overall behavior of density and temperature with height in the chromospheres and transition regions. Three possible explanations for the weakness of the coronal lines are presented, of which variability is perhaps the most likely.