X-ray Modeling of Very Young Early Type Stars in the Orion Trapezium: Signatures of Magnetically Confined Plasmas and Evolutionary Implications

Abstract

We analyzed high resolution X-ray spectra in the wavelength range of 1.5 -- 25 A of three of its X-ray brightest members obtained with the High Energy Transmission Grating Spectrometer (HETGS) on-board the Chandra X-ray Observatory. The DEM derived from over 80 emission lines in the spectrum of Theta Ori C indicates three peaks located at 7.9 MK, 25 MK, and 66 MK. The emission measure varies over the 15.4 day wind period of the star. For the two phases observed, the low temperature emission remains stable, while the high temperature emission shows significant differences. The line widths seem to show a similar bifurcation, where we resolve some of the soft X-ray lines with velocities up to 850 km/s, whereas the bulk of the lines remain unresolved. None of the lines are resolved for Theta Ori A and E. The high temperature emissivity contributes to most of the total X-ray flux in all stars. The bulk of the X-ray emission cannot be produced by shock instabilities in a radiation driven wind and are likely the result of magnetic confinement in all three stars. The fact that all stars appear to be magnetic and are near zero age on the main sequence also raises the issue whether the Orion stars are simply different or whether young massive stars enter the main sequence carrying significant magnetic fields.