title: Imaging the water snow-line during a protostellar outburst.
abstract: A snow-line is the region of a protoplanetary disk at which a major volatile, such as water or carbon monoxide, reaches its condensation temperature. Snow-lines play a crucial role in disk evolution by promoting the rapid growth of ice-covered grains. Signatures of the carbon monoxide snow-line (at temperatures of around 20 kelvin) have recently been imaged in the disks surrounding the pre-main-sequence stars TW Hydra and HD163296 (refs 3, 10), at distances of about 30 astronomical units (au) from the star. But the water snow-line of a protoplanetary disk (at temperatures of more than 100 kelvin) has not hitherto been seen, as it generally lies very close to the star (less than 5 au away for solar-type stars). Water-ice is important because it regulates the efficiency of dust and planetesimal coagulation, and the formation of comets, ice giants and the cores of gas giants. Here we report images at 0.03-arcsec resolution (12 au) of the protoplanetary disk around V883 Ori, a protostar of 1.3 solar masses that is undergoing an outburst in luminosity arising from a temporary increase in the accretion rate. We find an intensity break corresponding to an abrupt change in the optical depth at about 42 au, where the elevated disk temperature approaches the condensation point of water, from which we conclude that the outburst has moved the water snow-line. The spectral behaviour across the snow-line confirms recent model predictions: dust fragmentation and the inhibition of grain growth at higher temperatures results in soaring grain number densities and optical depths. As most planetary systems are expected to experience outbursts caused by accretion during their formation, our results imply that highly dynamical water snow-lines must be considered when developing models of disk evolution and planet formation.
authors.affiliation: Núcleo de Astronomía, Facultad de Ingeniería, Universidad Diego Portales, Av. Ejercito 441, Santiago 8370191, Chile.|Millenium Nucleus 'Protoplanetary Disks in ALMA Early Science', Av. Ejercito 441, Santiago 8370191, Chile.
authors.forename: Lucas A
authors.initials: LA
authors.lastname: Cieza
authors.affiliation: Millenium Nucleus 'Protoplanetary Disks in ALMA Early Science', Av. Ejercito 441, Santiago 8370191, Chile.|Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago 8330015, Chile.
authors.forename: Simon
authors.initials: S
authors.lastname: Casassus
authors.affiliation: Leiden Observatory, Leiden University, PO Box 9513, 2300RA Leiden, The Netherlands.
authors.forename: John
authors.initials: J
authors.lastname: Tobin
authors.affiliation: Leiden Observatory, Leiden University, PO Box 9513, 2300RA Leiden, The Netherlands.
authors.forename: Steven P
authors.initials: SP
authors.lastname: Bos
authors.affiliation: Institute for Astronomy, University of Hawaii at Manoa, Woodlawn Drive, Honolulu, Hawaii 96822, USA.
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Williams
authors.affiliation: Millenium Nucleus 'Protoplanetary Disks in ALMA Early Science', Av. Ejercito 441, Santiago 8370191, Chile.|Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago 8330015, Chile.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Perez
authors.affiliation: Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Peyton Hall, Princeton, New Jersey 08544, USA.
authors.forename: Zhaohuan
authors.initials: Z
authors.lastname: Zhu
authors.affiliation: Millenium Nucleus 'Protoplanetary Disks in ALMA Early Science', Av. Ejercito 441, Santiago 8370191, Chile.|Departamento de Física y Astronomía, Universidad Valparaiso, Av. Gran Bretaña 111, Valparaiso 2373195, Chile.
authors.forename: Claudio
authors.initials: C
authors.lastname: Caceres
authors.affiliation: Millenium Nucleus 'Protoplanetary Disks in ALMA Early Science', Av. Ejercito 441, Santiago 8370191, Chile.|Departamento de Física y Astronomía, Universidad Valparaiso, Av. Gran Bretaña 111, Valparaiso 2373195, Chile.
authors.forename: Hector
authors.initials: H
authors.lastname: Canovas
authors.affiliation: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA.
authors.forename: Michael M
authors.initials: MM
authors.lastname: Dunham
authors.affiliation: Joint ALMA Observatory, Alonso de Córdova 3107, Vitacura, Santiago 7630355, Chile.
authors.forename: Antonio
authors.initials: A
authors.lastname: Hales
authors.affiliation: Núcleo de Astronomía, Facultad de Ingeniería, Universidad Diego Portales, Av. Ejercito 441, Santiago 8370191, Chile.|Millennium Institute of Astrophysics, Av. Vicuña Mackenna 4860, Macul, Santiago 7820436, Chile.
authors.forename: Jose L
authors.initials: JL
authors.lastname: Prieto
authors.affiliation: Núcleo de Astronomía, Facultad de Ingeniería, Universidad Diego Portales, Av. Ejercito 441, Santiago 8370191, Chile.|Millenium Nucleus 'Protoplanetary Disks in ALMA Early Science', Av. Ejercito 441, Santiago 8370191, Chile.
authors.forename: David A
authors.initials: DA
authors.lastname: Principe
authors.affiliation: Millenium Nucleus 'Protoplanetary Disks in ALMA Early Science', Av. Ejercito 441, Santiago 8370191, Chile.|Departamento de Física y Astronomía, Universidad Valparaiso, Av. Gran Bretaña 111, Valparaiso 2373195, Chile.
authors.forename: Matthias R
authors.initials: MR
authors.lastname: Schreiber
authors.affiliation: Research School of Astronomy and Astrophysics, Australian National University, Canberra, Australian Capital Territory 2611, Australia.
authors.forename: Dary
authors.initials: D
authors.lastname: Ruiz-Rodriguez
authors.affiliation: Núcleo de Astronomía, Facultad de Ingeniería, Universidad Diego Portales, Av. Ejercito 441, Santiago 8370191, Chile.|Millenium Nucleus 'Protoplanetary Disks in ALMA Early Science', Av. Ejercito 441, Santiago 8370191, Chile.|Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago 8330015, Chile.
authors.forename: Alice
authors.initials: A
authors.lastname: Zurlo