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A. E. Glassgold, H. Shang, F.H. Shu (UCB), S. Lizano (UNAM)
Ambipolar diffusion and X-ray interactions have the potential to heat the inner part (or jet) of the X-wind. We have recalculated the ambipolar diffusion coupling coefficient for atomic regions (where H+ is the dominant ion) using recently calculated cross sections by Krstíc and Schultz and by others. The coefficient for hot regions (T \approx 104\, K) is an order of magnitude larger than the values used in the past because the short-range part of the H-H+ interaction (including exchange effects) is larger than previously assumed. Consequently ambipolar diffusion plays only a minor role in heating the inner part of the X-wind and very likely in YSO jets in general. We also find that X-ray heating is enhanced in atomic regions through the significant probability for populating excited levels of the H atom in collisions with X-ray induced secondary electrons (e.g., Dalgarno, Yan, and Liu 1999). The standard Lyman-alpha cooling must then be reduced by an amount that can be greater than direct collisional X-ray heating. The excess population in the n = 2 level leads to heating by collisional de-excitation in the presence of trapped Lyman-alpha line radiation. However, even with this enhancement, X-ray heating is usually less important than the main heating mechanism for the inner X-wind, which involves the dissipation of shock and turbulent energy. This research has been supported in part by the NSF.