The dust-rich (D-type) symbiotic stars appear always to comprise a mira variable and a star of temperature ∼ 105 K which ionizes the mira’s circumstellar envelope. On timescales of decades they change little, save for the slow pulsation of the mira at infrared wavelengths. RX Puppis is a striking exception to this generalization, however, since it undergoes extraordinary changes.

RX Pup drifts between two extremes, exhibiting intermediate states. Table I summarises the known characteristics in the extreme states. Because of its variability, models of RX Pup are more highly constrained, giving us a chance to understand one of the D-type symbiotics.

Optical spectra of RX Pup from the Anglo-Australian Telescope. Tie breadth of the lines in 1976 may be due to lower spectral resolution.