The infrared variability and nature of symbiotic stars. V. Seven more systems.

Infrared variability and spectra show that the symbiotic systems (He2 - 106, He2 - 38, He2 -34) contain Mira variable components. The first two also show a longer term infrared variability. It is suggested that this is due to variable dust obscuration (as in R Aqr). The phenomenon is then too frequent for the dust clouds to be confined to the orbital planes of the binary systems. Seven Miras in symbiotics have known periods which range from 370 to 580 days, suggesting a greater frequency of long-period Miras in symbiotics than in the general field. Symbiotic Miras have dust excesses with colour temperatures near 1000K. Observations of four other symbiotic systems (Pe2 - 3, He2 - 87, H2- 5, AG Peg) are consistent with their containing non-variable or low amplitude M-type components.