An unusual reservoir of water emission in the VV CrA A protoplanetary disk

Abstract

We present an analysis of an unusual pattern of water vapor emission from the $\sim$2 Myr-old low-mass binary system VV CrA, as observed in infrared spectra obtained with VLT-CRIRES, VLT-VISIR, and Spitzer-IRS. Each component of the binary shows emission from water vapor in both the L ($\sim 3\hat{I}¼$m) and N ($\sim 12\hat{I}¼$m) bands. The N-band and Spitzer spectra are similar to those previously observed from young stars with disks, and are consistent with emission from an extended protoplanetary disk. Conversely, the CRIRES L-band data of VV CrA A show an unusual spectrum, which requires the presence of a water reservoir with high temperature ($T\gtrsim 1500$ K), column density ($N_{H2O}\sim 3\times 10^{20}{\mathrm{cm}}^{-2}$), and turbulent broadening ($v\sim 10$ km s${}^{-1}$), but very small emitting area ($A\lesssim 0.005$ AU${}^2$). Similarity with previously observed water emission from V1331 Cyg (Doppmann et al. 2011) and SVS 13 (Carr et al. 2004) suggests that the presence of such a reservoir may be linked to evolutionary state, perhaps related to the presence of high accretion rates or winds. While the inner disk may harbor such a reservoir, simple Keplerian models do not match well with emitting line shapes, and alternative velocity fields must be considered. We also present a new idea, that the unusual emission could arise in a circumplanetary disk, embedded within the larger VV CrA A protoplanetary disk. Additional data are likely required to determine the true physical origin of this unusual spectral pattern.

32 pages, 17 figures, 5 appendix figures, 2 tables. Accepted for publication in ApJ