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

TL;DR

This study combines Spitzer and Herschel infrared observations to analyze the gas and dust composition of the evolved circumbinary disk around V4046 Sgr, revealing ongoing planet formation processes within 30 AU.

Contribution

It provides a comprehensive infrared spectral analysis of the V4046 Sgr disk, highlighting its gas and dust properties and evidence of planet-building activity in an evolved binary system.

Findings

Detection of multiple gas emission lines indicating active photodissociation.

Presence of large amorphous and crystalline silicate grains in the inner disk.

Evidence of ongoing planet formation within ~30 AU.

Abstract

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.