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P.R. Young, A.K. Dupree, S.J. Kenyon (Harvard-Smithsonian Center for Astrophysics), B. Espey (Space Telescope Science Institute), T.B. Ake (Department of Physics & Astronomy, The Johns Hopkins University and Computer Sciences Corporation)
AG Draconis (BD+67\circ922) is a yellow symbiotic star, consisting of a K0--K3 giant and hot compact object, thought to be a white dwarf. The hot star photoionizes the wind of the giant, giving a dense nebula rich in ionized species. The system undergoes increases in brightness by up to 3 magnitudes at irregular intervals, a phenomenon thought to be due to the triggering of nuclear burning on the hot star after the accretion of a critical mass of material from the giant wind.
The Far Ultraviolet Spectroscopic Explorer (FUSE) satellite observed AG Dra in March 2000 during a quiescent period. The spectrum covered the range 905--1187\,Å\ at a spectral resolution of ~15--20,000, and exhibits a number of emission lines from highly-ionised species, a continuum from the hot star, and absorption lines from the interstellar medium. The \ion{O}{6} \lambda\lambda1032, 1038 emission lines dominate the spectrum, with the \lambda1032 line showing evidence of a warm wind. Other species identified include \ion{Ne}{5}, \ion{Ne}{6}, \ion{S}{4}, \ion{S}{6} and the \ion{He}{2} Balmer lines. These lines help constrain the radiation field experienced by the nebula, and also the degree of extinction along the line of sight to AG Dra.
Measurements of the absorption lines of molecular hydrogen and the atomic species are used to infer properties of the interstellar medium in the direction of AG Dra.
FUSE is a NASA \emph{Origins} mission operated by the Johns Hopkins University. Funding for this work is provided through NASA contract NAS-532985.