Na. Tomov et al., Analysis of the U-band orbital variation of the symbiotic binary AG Draconis during quiescence, ASTRON ASTR, 364(2), 2000, pp. 557-562
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.