Dust Density Distribution and Imaging Analysis of Different Ice Lines in Protoplanetary Disks

Abstract

Recent high angular resolution observations of protoplanetary disks at different wavelengths have revealed several kinds of structures, including multiple bright and dark rings. Embedded planets are the most used explanation for such structures, but there are alternative models capable of shaping the dust in rings as it has been observed. We assume a disk around a Herbig star and investigate the effect that ice lines have on the dust evolution, following the growth, fragmentation, and dynamics of multiple dust size particles, covering from 1 μm to 2 m sized objects. We use simplified prescriptions of the fragmentation velocity threshold, which is assumed to change radially at the location of one, two, or three ice lines. We assume changes at the radial location of main volatiles, specifically H 2 O, CO 2 , and NH 3 . Radiative transfer calculations are done using the resulting dust density distributions in order to compare with current multiwavelength observations. We find that the structures in the dust density profiles and radial intensities at different wavelengths strongly depend on the disk viscosity. A clear gap of emission can be formed between ice lines and be surrounded by ring-like structures, in particular between the H 2 O and CO 2 (or CO). The gaps are expected to be shallower and narrower at millimeter emission than at near-infrared, opposite to model predictions of particle trapping. In our models, the total gas surface density is not expected to show strong variations, in contrast to other gap-forming scenarios such as embedded giant planets or radial variations of the disk viscosity.

Self-induced dust traps around snow lines in protoplanetary discs

“…We also should not find large grains exterior to the CO snow line because grains are not allowed to grow there. This is consistent with what Pinilla et al (2017) found in their model II for α = 10 −2 (the closest to our model), where dust growth only happens between the water ice line and the CO 2 line. However, as they do not take back-reaction into account on the gas evolution, they do not see any decoupling of the dust with respect to the gas, as opposed to us.…”

“…This means that when CO freezes-out on the surface of grains, it weakens them. This has been proposed by Pinilla et al (2017), where they chose to assimilate the behaviour of CO 2 -covered grains with that of silicates, i.e. that their fragmentation velocity is of the order of 1 m s −1 .…”

A Multifrequency ALMA Characterization of Substructures in the GM Aur Protoplanetary Disk

“…While the N 2 H + distribution may suggest an association between the dust substructures and snowlines, the appearance of the GM Aur disk in scattered light does not. Models from Pinilla et al (2017) indicate that snowline-induced dust substructures should be deeper and wider in near-infrared scattered light images compared to millimeter/sub-millimeter images. However, no clear substructures are observed in the Subaru HiCIAO H−band polarized intensity image of GM Aur from Oh et al (2016).…”

The Circumstellar Disk HD 169142: Gas, Dust, and Planets Acting in Concert?*

“…Ice lines of different volatile species can significantly affect the dynamics of dust evolution processes including growth and fragmentation, which in turn has an effect on the observational appearance of rings and gaps at different wavelengths (Pinilla et al 2017). The freeze-out temperatures of the main volatiles, such as water (H 2 O), ammonia (NH 3 ), carbon dioxide (CO 2 ), and carbon monoxide (CO), are estimated to have average values of ∼142, ∼80, ∼66, and ∼26 K, respectively (Zhang et al 2015).…”

“…Various mechanisms have been proposed in the literature that can be assigned to three main categories: structures caused by fluid dynamics, dust evolution effects, and planet-disk perturbations. More precisely, these possibilities include zonal flows from magneto-rotational instability (e.g., Simon & Armitage 2014;Béthune et al 2016), gap/bump structures in the surface density close to the dead-zone outer edge (e.g., Flock et al 2015;Pinilla et al 2016;Ruge et al 2016), efficient particle growth at condensation fronts near ice lines or a depletion of solid material between ice lines (Zhang et al 2015;Pinilla et al 2017;Stammler et al 2017), aggregate sintering zones (Okuzumi et al 2016), secular gravitational instabilities (Youdin 2011;Takahashi & Inutsuka 2014), or planet-disk interactions (e.g., Zhu et al 2011Zhu et al , 2012Dong et al 2015Dong et al , 2016Rosotti et al 2016). Finally, dips or dark regions can be interpreted as shadows by inner disk material (e.g., Marino et al 2015;Pinilla et al 2015b;Stolker et al 2016;Canovas et al 2017).…”