A Combined Spitzer and Herschel Infrared Study of Gas and Dust in the Circumbinary Disk Orbiting V4046 Sgr

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 InfraRed Spectrograph spectra show emission lines of [Ne ii], H₂ S(1), CO₂, and HCN, while Herschel Photodetector Array Camera and Spectrometer and Spectral and Photometric Imaging Receiver spectra reveal emission from [O i], OH, and tentative detections of H₂O 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 H₂ 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, H₂O, 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 μm) 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.