Analysis of the U-band orbital variation of the symbiotic binary AG Draconis during quiescence

The photometric U orbital variations of the symbiotic binary AG Dra, caused by occultation of a bright gaseous region by the K giant in this system, a re used to derive the emission from the circumbinary nebula, that is suppos ed to be generated by the cool giant's wind. Assuming spherical symmetry an d constant expansion velocity for the wind, and that the giant has the same intrinsic continuum energy distribution of alpha Boo, we derive a cool gia nt's radius of 28 divided by 32 R. and a distance of 1560 divided by 1810 p c. We conclude that the cool giant does not fill its Roche lobe, which is c ontrasting with the intense, accretion powered X-ray emission.