title: Ringed Structures of the HD 163296 Protoplanetary Disk Revealed by ALMA.
abstract: We present Atacama Large Millimeter and Submillimeter Array observations of the protoplanetary disk around the Herbig Ae star HD 163296 that trace the spatial distribution of millimeter-sized particles and cold molecular gas on spatial scales as small as 25 astronomical units (A.U.). The image of the disk recorded in the 1.3 mm continuum emission reveals three dark concentric rings that indicate the presence of dust depleted gaps at about 60, 100, and 160 A.U. from the central star. The maps of the ^{12}CO, ^{13}CO, and C^{18}O J=2-1 emission do not show such structures but reveal a change in the slope of the radial intensity profile across the positions of the dark rings in the continuum image. By comparing the observations with theoretical models for the disk emission, we find that the density of CO molecules is reduced inside the middle and outer dust gaps. However, in the inner ring there is no evidence of CO depletion. From the measurements of the dust and gas densities, we deduce that the gas-to-dust ratio varies across the disk and, in particular, it increases by at least a factor 5 within the inner dust gap compared to adjacent regions of the disk. The depletion of both dust and gas suggests that the middle and outer rings could be due to the gravitational torque exerted by two Saturn-mass planets orbiting at 100 and 160 A.U. from the star. On the other hand, the inner dust gap could result from dust accumulation at the edge of a magnetorotational instability dead zone, or from dust opacity variations at the edge of the CO frost line. Observations of the dust emission at higher angular resolution and of molecules that probe dense gas are required to establish more precisely the origins of the dark rings observed in the HD 163296 disk.
authors.affiliation: Department of Physics and Astronomy, Rice University, 6100 Main Street, MS-108, Houston, Texas 77005, USA.
authors.forename: Andrea
authors.initials: A
authors.lastname: Isella
authors.affiliation: INAF/Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy.
authors.forename: Greta
authors.initials: G
authors.lastname: Guidi
authors.affiliation: INAF/Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy.|ESO, Karl Schwarzschild str. 2, 85748 Garching bei Mnchen, Germany.
authors.forename: Leonardo
authors.initials: L
authors.lastname: Testi
authors.affiliation: Department of Physics and Astronomy, Rice University, 6100 Main Street, MS-108, Houston, Texas 77005, USA.|Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
authors.forename: Shangfei
authors.initials: S
authors.lastname: Liu
authors.affiliation: Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
authors.forename: Hui
authors.initials: H
authors.lastname: Li
authors.affiliation: Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
authors.forename: Shengtai
authors.initials: S
authors.lastname: Li
authors.affiliation: Department of Physics and Astronomy, Rice University, 6100 Main Street, MS-108, Houston, Texas 77005, USA.
authors.forename: Erik
authors.initials: E
authors.lastname: Weaver
authors.affiliation: Department of Physics and Astronomy, Rice University, 6100 Main Street, MS-108, Houston, Texas 77005, USA.
authors.forename: Yann
authors.initials: Y
authors.lastname: Boehler
authors.affiliation: Joint ALMA Observatory (JAO), Alonso de Cordova 3107 Vitacura, Santiago de Chile, Chile.
authors.forename: John M
authors.initials: JM
authors.lastname: Carperter
authors.affiliation: Joint ALMA Observatory (JAO), Alonso de Cordova 3107 Vitacura, Santiago de Chile, Chile.
authors.forename: Itziar
authors.initials: I
authors.lastname: De Gregorio-Monsalvo
authors.affiliation: Scientific Support Office, Directorate of Science, European Space Research and Technology Centre (ESA/ESTEC), Keplerlaan 1, 2201 AZ Noordwijk, Netherlands.
authors.forename: Carlo F
authors.initials: CF
authors.lastname: Manara
authors.affiliation: INAF/Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy.|School of Cosmic Physics, Dublin Institute for Advanced Studies, 31 Fitzwilliams Place, 2 Dublin, Ireland.
authors.forename: Antonella
authors.initials: A
authors.lastname: Natta
authors.affiliation: Max-Planck-Institut fr Radioastronomie Bonn, auf dem Hgel 69, D-53121 Bonn, Germany.
authors.forename: Laura M
authors.initials: LM
authors.lastname: Pérez
authors.affiliation: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA.
authors.forename: Luca
authors.initials: L
authors.lastname: Ricci
authors.affiliation: Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, California 91125, USA.
authors.forename: Anneila
authors.initials: A
authors.lastname: Sargent
authors.affiliation: ESO, Karl Schwarzschild str. 2, 85748 Garching bei Mnchen, Germany.
authors.forename: Marco
authors.initials: M
authors.lastname: Tazzari
authors.affiliation: Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA.
authors.forename: Neal
authors.initials: N
authors.lastname: Turner