Stellar Outburst Brings Water Snowline into View

A snow-line is the region of a protoplanetary disk at which a major volatile reaches its condensation temperature. They play a crucial role in disk evolution by promoting the rapid growth of ice-covered grains. Signatures of the carbon monoxide snow-line, at T ~ 20 deg K, have recently been imaged in the disks surrounding the pre-main-sequence stars TW Hydra and HD163296 at distances of ~ 30 AU from the star. But the water snow-line of a protoplanetary disk, at temperatures of more than 100 deg K, has not been seen, as it typically is less than 5 AU from solar-type stars. Water-ice is important because it regulates dust and planetesimal coagulation efficiency, and the formation of comets, ice giants, and the cores of gas giants. Cieza et al. present ALMA images at 0.03 arcsec resolution (12 AU) of the protoplanetary disk around V883 Ori, a 1.3 M_⊙ protostar undergoing a luminosity outburst owing to a temporary accretion rate increase. The authors find an intensity break corresponding to an abrupt optical depth change at ~ 42 AU, where the elevated disk temperature approaches water’s condensation point, and conclude that the outburst has moved the water snow-line. The spectral behavior across the snow-line confirms model predictions that dust fragmentation and the inhibition of grain growth at higher temperatures results in soaring grain number densities and optical depths. As most forming planetary systems are expected to experience outbursts caused by accretion, these results imply that highly dynamical water snow-lines must be considered when developing models of disk evolution and planet formation.

Image: Artist impression of the water snowline around the young star V883 Orionis, as observed with ALMA.  Credit: A. Angelich (NRAO/AUI/NSF).

Science Team: Lucas A. Cieza (Diego Portales), Simon Casassus, (Univ. de Chile), John Tobin (Leiden), Steven P. Bos, (Leiden), Jonathan P. Williams (Hawaii-Manoa), Sebastian Perez (Univ. de Chile), Zhaohuan Zhu (Princeton), Claudio Caceres (Univ. Valparaiso), Hector Canovas (Univ. Valparaiso), Michael M. Dunham (CfA), Antonio Hales (JAO), Jose L. Prieto (Diego Portales), David A. Principe, (Diego Portales), Matthias R. Schreiber (Valparaiso), Dary Ruiz-Rodriguez (Australian National Univ.), and Alice Zurlo (Diego Portales, Univ. de Chile).

Publication: Imaging the Water Snow-line During a Protostellar Outburst, 2016, Nature, 535, 258.