4.3. Double Stars and Symbiotic Stars ( ~ 1010 km; ~ 10-3 pc)
Binary (double-star) systems hold important clues to stellar magnetism. RS Canum Venaticorum shows optical light variations which differ from the orbital period, thus implying the presence of starspots and associated magnetic fields on one star of this system. Others show the presence of polarized radio emission from synchrotron electrons trapped in a magnetic field. The presence of a strong magnetic field in a close binary system can modify the standard structure of the system.
Symbiotic stars are interacting binary stars, with an orbital period of years to decades. One of the two stars in interaction is a late-type red giant star or a Mira variable star, emitting a stellar wind that goes around the system (circumbinary gas). The other star in the interaction is a source of ionization for a circumbinary wind. Typical values for the circumstellar gas are: electron density n ~ 107 cm-3, electron temperature ~ 15000 K, dust temperature ~ 460 K, size ~ 100 AU ( 1.5 × 1010 km), so the nebular mass ~ 10-6 M (Schulte-Ladbeck 1988). Significant mass loss is occurring from the red giant star, with a portion of that neutral gas being ionized by a hot star somewhere in the wind - there is radio emission from the ionized gas (Seaquist et al. 1984). Here most of the variation in intensity and polarization may be due to asymmetric mass loss and asymmetric dust distribution and dust/molecule scattering (Moffat 1988), not to aligned dust in magnetic fields.