Line formation of cool carbon star chromospheres

Based on adopted photospheric plus chromospheric models, we generate synthetic fluxes of the C II (UV 0.01) and both fluxes and profiles for the Mg II (UV 1) lines in both complete (CRD) and partial (PRD) redistribution and compare them to IUE spectra of the carbon star TX Psc. Non-LTE calculations with the program, PANDORA are made for H, C, Na, Mg, and Ca. For CRD and a well constrained chromospheric model, the best fit to the Mg II line profiles gives a flux in the C II lines (produced surprisingly, at the same depth as the Mg II lines) 2.6 times too great and produces too much emission in the Mg II line wings. PRD in the Mg II h and k lines in an expanding chromosphere with an adjusted temperature structure produces the observed Mg II emission. The reduction in temperature produces C II fluxes that match the IUE low resolution spectra