The infrared variability and nature of symbiotic stars.

Results are presented for broadband JHKL infrared photometry of three symbiotic star systems containing an M-type giant (RW Hya, SY Mus, AG Peg), three symbiotic systems exhibiting emission attributed to heated dust (RX Pup, RR Tel, PK 280-2.1 deg), and the VV Cephei system FR Sct. No clear evidence is found for IR variability in the systems without dust emission, and the red component of FR Sct is suggested to be a supergiant. For the systems exhibiting dust emission, IR variations are detected whose amplitude decreases with increasing wavelength. It is proposed that the symbiotic stars without extensive dust emission contain normal nonvariable M giants, while the systems with dust emission contain Mira variables. The possibility is considered that mass transfer in symbiotic systems containing Miras could be accomplished via accretion of a strong stellar wind flowing from the Mira component to the collapsed component.