Abstract
The authors have for the first time discovered the existence of two temperature components in the X-ray emission from planetary nebulae. The observed ROSAT PSPC spectrum of the Helix Nebula exhibits a strong peak at about 0.12 keV and a secondary peak at about 0.8 keV. The best model fit results in a temperature of T1 = 1.4×105K for the low-energy component, and a temperature T2 = 8.7×106K for the high-energy component, at hydrogen column density NH = 1.41×1020cm-2. The low-energy component can be attributed to the photosphere of the central star. The high-energy component may be caused by a stellar corona. An alternative explanation is that this hot component is due to plasma in a hot bubble predicted by the interacting wind model. A lower limit of the electron density in the hot plasma is about 10 cm-3.
