  We present results from a spectroscopic Spitzer and Herschel
mid-to-far-infrared study of the circumbinary disk orbiting the evolved (age
~12-23 Myr) close binary T Tauri system V4046 Sgr. Spitzer IRS spectra show
emission lines of [Ne II], H_2 S(1), CO_2 and HCN, while Herschel PACS and
SPIRE spectra reveal emission from [O I], OH, and tentative detections of H_2O
and high-J transitions of CO. We measure [Ne III]/[Ne II] < 0.13, which is
comparable to other X-ray/EUV luminous T Tauri stars that lack jets. We use the
H_2 S(1) line luminosity to estimate the gas mass in the relatively warm
surface layers of the inner disk. The presence of [O I] emission suggests that
CO, H_2O, and/or OH is being photodissociated, and the lack of [C I] emission
suggests any excess C may be locked up in HCN, CN and other organic molecules.
Modeling of silicate dust grain emission features in the mid-infrared indicates
that the inner disk is composed mainly of large (r~5 um) amorphous pyroxene and
olivine grains (~86% by mass) with a relatively large proportion of crystalline
silicates. These results are consistent with other lines of evidence indicating
that planet building is ongoing in regions of the disk within ~30 AU of the
central, close binary.
