Changes in IUE postmaximum spectra of the Mira variable chi Cygni.

International Ultraviolet Explorer long-wavelength (2500 - 3350 A) spectra of the long-period variable chi Cygni were obtained at phases phi = 0.04, 0.18, and 0.22 following the 1979 light maximum. Low spectral resolution was used except for the last phase studied where a high resolution spectrum was secured. At phase 0.04, the Fe II (V1) emission lines are outstanding features together with absorption lines as the Fe I (V9) lines. The Mg II h and k emission doublet is absent: instead an absorption feature appeared suggesting re-absorption by an outer layer. Two months later, at phi = 0.18, other emission lines appeared in the low resolution spectrum as the Mg II doublet and the Fe II (UVI) lines. Their high resolution asymmetric profiles (at phase 0.22) are discussed. These observations are interpreted on the basis of a shock wave model.