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A.E. Wehrle (Interferometry Science Center, Caltech and Jet Propulsion Laboratory), M.J. Creech-Eakman (Jet Propulsion Laboratory)
The intereacting binary star Z Andromedae contains a white dwarf and red giant embedded in an ionized envelope (binary period of 759 days). It is heavily observed as the archetype of symbiotic stars. An envelope of gas and dust is thought to be the origin of optical emission lines as well as Raman scattering; the red giant ejects the material and the white dwarf ionizes it. Thermal bremstraahlung from the shell is detected in the radio at the 1-mJy level at cm wavelengths. Additional periodicity in the stellar system's brightness occurs when accreting mass falls onto the white dwarf and the resulting thermonuclear reactions cause quasiperiodic oscillations. We observed the star during its recent outburst with the Palomar Testbed Interferometer for three reasons: first, new instrumentation always reveals something new about archetypes; second, to measure the possibly non-spherical angular diameter of the red giant in the system; and third, to see if it is a suitable target for comparing the radio, near-infrared, and optical positions, as is done for reference-frame-tie objects.
This work is funded by the NASA Origins Program through JPL and Caltech. We thank the PTI Collaboration members.
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.