ELECTRON-ION EQUILIBRATION IN NONRADIATIVE SHOCKS ASSOCIATED WITH SN-1006

The ultraviolet spectrum of SN 1006 observed by the Hopkins Ultraviole t Telescope (HUT) is modeled to infer the degree of electron-ion equil ibration at the nonradiative shocks in the remnant. Such an approach i s possible since the spectrum has lines (He II lambda 1640) whose exci tation is dominated by electrons, and others (C IV lambda 1550, N V la mbda 1240, O VI lambda 1036) in which protons and other ions are more important, and the intensity ratio between these is sensitive to the e lectron-ion temperature ratio. We find substantially less than full eq uilibration, marginally consistent with existing plasma simulations bu t rather more suggestive of even lower equilibration than these studie s would predict. The more stringent limits on the electron temperature resulting from this allow a more accurate determination of the distan ce to SN 1006. Our result is 1.8 +/- 0.3 kpc.