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Abstract

In addition, comparing the spectral type and luminosity of θ¹ Ori C with the recent calibrations of P. Massey et al. (ApJ, 628, 986 [2005]) and F. Martins et al. (ApJ, 628, 986 [2005]) suggests that θ¹ Ori C is an O5.5 V star with radius R~10.6 R_solar and effective temperature T_eff~40,000 K. This new calibration makes θ¹ Ori C larger and cooler than both the ``hot'' and ``cool'' models in Table 3 of our original paper.

In the revised Figure 13 below, we show the corrected PRISMSPECT line ratios for Mg XI, Si XIII, and S XV as a function of u=R_*/R for T_eff=40,000 K. Also shown are the predictions from the analytic parametrization of G. R. Blumenthal et al. (ApJ, 628, 986 [2005]). For Mg XI and Si XIII, we further show the predictions based on the R₀ values of D. Porquet et al. (ApJ, 628, 986 [2005]). The hatched regions in Figure 13 represent the 1 σ upper and lower bounds on f/i from the HETG data and u=R_*/R from the PRISMSPECT model. Although the three f/i ratios yield different bounds on the formation radius, there is a range of radii, 1.7<R/R_*<2.1, that is consistent with all three measured f/i ratios. Using G. R. Blumenthal et al. (ApJ, 628, 986 [2005]) (Fig. 13, solid lines), the range of radii is 1.6<R/R_*<2.0. The net effect of the corrected model and lower effective temperature is to place the X-ray-emitting plasma at a slightly larger radius than reported originally.

Figure 5c added here is a gray-scale image of emission measure per unit volume from the 375 ks snapshot of the MHD simulation shown in the upper and lower panels of Figure 5 of the original paper. Overlaid on the emission-measure map is a T=10⁶ K contour. The new Figure 5c shows that the X-rays in the magnetically channeled wind shock (MCWS) model are formed over a range of radii, with an effective emission radius R~2R_*, consistent with the revised f/i ratio calculations.

Thus, the only remaining discrepancy between the HETG data and the MCWS model is the overall X-ray variability, 1-L^min_X/L^max_X~0.33. If the X-rays are produced, on average, at R~2R_*, then occultation of an X-ray torus by the photosphere would produce a ~17% dip in visible X-ray luminosity at phase 0.5, only about half the observed drop. We suggest that the remaining absorption must occur in the dense gas in the magnetic equatorial plane. To test this idea, future absorption models will need to properly account for the ionization of the outflowing circumstellar plasma.

M. R. G. and D. H. C. would like to thank Swarthmore College students Micah Walter-Range for uncovering the PRISMSPECT modeling error and Steve St. Vincent for producing Figure 5c.

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