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.

The Kinematics and Excitation of Infrared Water Vapor Emission from Planet-forming Disks: Results from Spectrally Resolved Surveys and Guidelines for JWST Spectra

“…Other studies analyzed small samples of high-resolution spectra from the ground, mostly biased toward highly accreting disks that had been observed with Spitzer to have strong water emission; these spectra provided first kinematic information on the water emission but were very limited in sensitivity and by strong telluric absorption (Pontoppidan et al 2010b;Salyk et al 2019) and, in the case of the 2.9 μm water band, by absorption in stellar photospheres (Banzatti et al 2017). The properties of water emission as observed in different samples and different wavelengths have ranged from high temperatures in very optically thick regions in the L band (T ≈ 1500 K and N ≈ 10 20 cm −2 , found in only three disks so far; Carr et al 2004;Doppmann et al 2011;Salyk et al 2022), to moderate temperatures and opacity in a narrow window in the N band (T ≈ 500-700 K and N ≈ 10 18 cm −2 ; Najita et al 2018;Salyk et al 2019), down to cooler temperatures at mid-and farinfrared wavelengths (300-600 K; Salyk et al 2011b;Riviere-Marichalar et al 2012;Liu et al 2019). Apart from those analyzing Spitzer spectra, previous results were always based on small samples of 1-10 bright sources.…”

“…Water rovibrational emission spectra at 2.9-2.98 μm are included as observed with CRIRES (Kaeufl et al 2004) Brown et al 2013). The water spectra were obtained for ≈50% of the sample in that survey (35 out of 69 disks, mostly T Tauri stars) and were presented and analyzed in Banzatti et al (2017), except for the very different spectrum with a much larger number of high-excitation lines observed in VV CrA S, which is published in Salyk et al (2022). Additional spectra for 11 Herbig Ae/Be stars were presented in Fedele et al (2011).…”

CORINOS. I. JWST/MIRI Spectroscopy and Imaging of a Class 0 Protostar IRAS 15398–3359

“…At mid-infrared wavelengths, rotationally excited H 2 lines and ionic forbidden lines trace the shocked gas and jets in outflow cavities (e.g., Lahuis et al 2010). Furthermore, rovibrational CO lines and water vapor emission at ∼4-6 μm highlight the shocked gas at the base of outflows and/or at the disk surface, constraining the physical conditions of outflows and disks (e.g., Herczeg et al 2011;Salyk et al 2022).…”