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 ∼2 Myr old low-mass binary system VV CrA, as observed in IR spectra obtained with VLT-CRIRES, VLT-VISIR, and Spitzer-IRS. Each component of the binary shows emission from water vapor in both the L (∼3 μm) and N (∼12 μm) 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 ≳ 1500 K), column density (N_(H2O) ∼ 3 × 10²⁰ cm⁻²), and turbulent broadening (v ∼ 10 km s⁻¹) but very small emitting area (A ≲ 0.005 au²). Similarity to previously observed water emission from V1331 Cyg and SVS 13 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.