Resolved Images of Large Cavities in Protoplanetary Transition Disks

Abstract

Circumstellar disks are thought to experience a rapid "transition" phase in their evolution that can have a considerable impact on the formation and early development of planetary systems. We present new and archival high angular resolution (0. ′′ 3 ≈ 40-75 AU) Submillimeter Array (SMA) observations of the 880 µm (340 GHz) dust continuum emission from 12 such transition disks in nearby star-forming regions. In each case, we directly resolve a dust-depleted disk cavity around the central star. Using two-dimensional Monte Carlo radiative transfer calculations, we interpret these dust disk structures in a homogeneous, parametric model framework by reproducing their SMA continuum visibilities and spectral energy distributions. The cavities in these disks are large (R cav = 15-73 AU) and substantially depleted of small (∼µm-sized) dust grains, although their mass contents are still uncertain. The structures of the remnant material at larger radii are comparable to normal disks. We demonstrate that these large cavities are relatively common among the millimeter-bright disk population, comprising at least 1 in 5 (20%) of the disks in the bright half (and ≥26% of the upper quartile) of the millimeter luminosity (disk mass) distribution. Utilizing these results, we assess some of the physical mechanisms proposed to account for transition disk structures. As has been shown before, photoevaporation models do not produce the large cavity sizes, accretion rates, and disk masses representative of this sample. It would be difficult to achieve a sufficient decrease of the dust optical depths in these cavities by particle growth alone: substantial growth (to meter sizes or beyond) must occur in large (tens of AU) regions of low turbulence without also producing an abundance of small particles. Given those challenges, we suggest instead that the observations are most commensurate with dynamical clearing due to tidal interactions with low-mass companions -young brown dwarfs or giant planets on long-period orbits. Subject headings: circumstellar matter -protoplanetary disks -planet-disk interactions -planets and satellites: formation -submillimeter: planetary systems

The long-term evolution of photoevaporating transition discs with giant planets

“…The process depends sensitively on the mass of the planet and accretion rate; if this is too small, this effect is not strong enough, and the small dust will flow in the gap. This is consistent with several existing observations, which show a hole at mm wavelength, but have the SED of a primordial disc (Andrews et al 2011). …”

“…If all discs go through the transition disc phase, this implies that this phase must be short-lived (of order of 10 5 years), implying that disc evolution observes a "two-time scale behaviour". Transition discs have also been imaged by sub-mm interferometers (Piétu et al 2006;Brown et al 2009;Andrews et al 2011;Isella et al 2012), confirming the presence of huge (tens of AU) cavities in the mm-dust.…”

Slowly-growing gap-opening planets trigger weaker vortices

“…Aside from the discrepancy with observed disc masses (Andrews et al 2011), this very high surface density is incompatible with the assumption of a low-disc viscosity, because it corresponds to a disc with a small Toomre Q. For the passive irradiated disc profile from Chiang & Goldreich (1997) [see their equation (14a)] with…”

The Depletion of Water During Dispersal of Planet-Forming Disk Regions

“…Evidence is growing that there is at least one mode of disk dispersal, working from the inside out. Observations of a wavelength-dependent decrease in infrared excesses (e.g., Skrutskie et al 1990;Haisch et al 2001;Espaillat et al 2012;Ribas et al 2015), or spatially resolved cavities in continuum dust emission (e.g., Andrews et al 2011;van der Marel et al 2016), indicate that dust grains in the inner disk regions are depleted before those at larger radii. Disks that show these properties have been proposed to be in a transition phase ("transitional disks") toward their dispersal (e.g., Strom et al 1989;Skrutskie et al 1990;Takeuchi & Artymowicz 2001).…”