A Multi-ringed, Modestly Inclined Protoplanetary Disk around AA Tau

Abstract

AA Tau is the archetype for a class of stars with a peculiar periodic photometric variability thought to be related to a warped inner disk structure with a nearly edge-on viewing geometry. We present high resolution (∼0 2) ALMA observations of the 0.87 and 1.3mm dust continuum emission from the disk around AA Tau. These data reveal an evenly spaced three-ringed emission structure, with distinct peaks at 0 34, 0 66, and 0 99, all viewed at a modest inclination of 59°.1±0°.3 (decidedly not edge-on). In addition to this ringed substructure, we find nonaxisymmetric features, including a "bridge" of emission that connects opposite sides of the innermost ring. We speculate on the nature of this "bridge" in light of accompanying observations of HCO + and 13 CO (J=3-2) line emission. The HCO + emission is bright interior to the innermost dust ring, with a projected velocity field that appears rotated with respect to the resolved disk geometry, indicating the presence of a warp or inward radial flow. We suggest that the continuum bridge and HCO + line kinematics could originate from gap-crossing accretion streams, which may be responsible for the long-duration dimming of optical light from AA Tau.

Spiral Arms in Disks: Planets or Gravitational Instability?

“…More graphically, high-resolution submillimeter continuum images of disks made with ALMA commonly show stunning rings and gaps (ALMA Partnership et al 2015;Andrews et al 2016;Cieza et al 2016Cieza et al , 2017Isella et al 2016;Loomis et al 2017;Dipierro et al 2018;Fedele et al 2018;Huang et al 2018), structures that signal that disk solids have grown beyond centimeter sizes and possibly into planetary-mass objects (e.g., Dipierro et al 2015;Dong et al 2015cDong et al , 2017a). These results exclaim that disks are highly evolved and call into question disk mass estimates made under the usual assumption of simple, unevolved, optically thin disks.…”

A UV-to-NIR Study of Molecular Gas in the Dust Cavity around RY Lupi

“…1±0°. 3 for the outermost dust rings (Loomis et al 2017), compared to the 75°that was previously determined from scattered light measurements (O'Sullivan et al 2005). The warp model is no longer able to explain the dimming events in this system if the inner disk is also at this lower inclination, so it is proposed instead that the inner disk is misaligned and closer to edge-on.…”

Protoplanetary Disks in ρ Ophiuchus as Seen from ALMA

“…Such gaps in the millimeter emission from the disk have been directly imaged previously in the young Class I/II object HL Tau (ALMA Partnership et al 2015) and the nearby older Class II TW Hya (Andrews et al 2016;Nomura et al 2016), as well as in the higher-mass Herbig Ae stars HD 163296 (Isella et al 2016) and HD 169142 (Fedele et al 2017). Modeling of ALMA continuum data at 0.87 and 1.3 mm of the young Class II star AA Tau also suggests multiple gaps in this star's disk (Loomis et al 2017). The leading candidates for how the gaps open are either that a forming protoplanet/gas-giant core gravitationally torques material around it, effectively repelling some disk material away from it (Lin & Papaloizou 1986), or through enhanced grain growth due to pressure bumps caused by planets (Birnstiel et al 2010).…”