M. Badiali Istituto di Astrofisica Spaziale, CNR, Frascati (Roma), Italy
The HIPPARCOS astrometric satellite has observed a number of
symbiotic stars which are also known for being mapped at radio wavelengths. The
radio emission generally arises from matter ejected by the binary system, which is
made visible by the ionizing radiation of the system's hot component.
HIPPARCOS has provided the astrometric position (with milliarcsecond
precision), proper motion, and distance (or a lower limit to it) of a few symbiotic
stars. The most interesting results are those for CH Cygni and R Aquarii, for which
there is a significant displacement of the radio-continuum and optical position. The
position of the radio maser emission of R Aqr is also discussed.
We shall also report on the HIPPARCOS data for EG Andromedae, AG Draconis,
AG Pegasi, and other peculiar variables.