Abstract
We present non-LTE calculations for the ionization equilibrium of C I tailored to match the HgMn star χ Lupi. Comparisons are made with the UV C I lines observed using the Hubble Space Telescope's Goddard High Resolution Spectrograph, as well as with Voyager far-ultraviolet (FUV) measurements of the flux between 1040 and 1200 Å, where C I is the dominant continuum opacity source. The non-LTE models do provide better fits to most C I line profiles than do the LTE models, but the expected increase in the FUV continuum flux due to the non-LTE underpopulation of the lower levels of carbon is largely masked by uncertainties in the Voyager data and in the FUV line blanketing. Realistic modeling of the C I ionization equilibrium required including the FUV opacity from the predicted lines of iron-group elements, and to this end the non-LTE model atmosphere program TLUSTY was modified to include opacity distribution functions of Kurucz as a fixed-opacity source. This modified code will be useful for studying non-LTE effects in other ions in χ Lupi and similar stars.
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