Annular substructures in the transition disks around LkCa 15 and J1610

Abstract

We present high-resolution millimeter continuum ALMA observations of the disks around the T Tauri stars LkCa 15 and 2MASS J16100501-2132318 (hereafter, J1610). These transition disks host dust-depleted inner regions, which have possibly been carved by massive planets, and they are of prime interest to the study of the imprints of planet-disk interactions. While at moderate angular resolution, they appear as a broad ring surrounding a cavity, the continuum emission resolves into multiple rings at a resolution of ~60 × 40 mas (~7.5 au for LkCa 15, ~6 au for J1610) and ~7 μJy beam−1 rms at 1.3 mm. In addition to a broad extended component, LkCa 15 and J1610 host three and two narrow rings, respectively, with two bright rings in LkCa 15 being radially resolved. LkCa 15 possibly hosts another faint ring close to the outer edge of the mm emission. The rings look marginally optically thick, with peak optical depths of ~0.5 (neglecting scattering), in agreement with high angular resolution observations of full disks. We performed hydrodynamical simulations with an embedded, sub-Jovian-mass planet and show that the observed multi-ringed substructure can be qualitatively explained as the outcome of the planet-disk interaction. We note, however, that the choice of the disk cooling timescale alone can significantly impact the resulting gas and dust distributions around the planet, leading to different numbers of rings and gaps and different spacings between them. We propose that the massive outer disk regions of transition disks are favorable places for planetesimals, and possibly second-generation planet formation of objects with a lower mass than the planets carving the inner cavity (typically few MJup), and that the annular substructures observed in LkCa 15 and J1610 may be indicative of planetary core formation within dust-rich pressure traps. Current observations are compatible with other mechanisms contributing to the origin of the observed substructures, in particular with regard to narrow rings generated (or facilitated) at the edge of the CO and N2 snowlines.

Probing inner and outer disk misalignments in transition disks

“…• ) and that is obtained from continuum ALMA observations (50.16 • ± 0.03 • ; Facchini et al 2020) and suggests that the outer disk is misaligned with respect to the star+inner disk system. Similarly, in DoAr 44, Bouvier et al (2020) find that the stellar inclination is i = 30 • ± 5 • in agreement with our estimate of the inner disk inclination.…”

A bright inner disk and structures in the transition disk around the very low-mass star CIDA 1

“…Recent observations with ALMA of several transition disks showed that what was known to be a wide ring around a cavity is actually a composition of several narrow rings (e.g., Pérez et al 2020;Facchini et al 2020). A couple of ideas have been proposed to explain these narrow rings.…”

“…Pérez et al (2020) suggested that a single migrating low-mass planet (10 M ⊕ ) in between these rings can explain the multiple rings and their separation, but this planet cannot explain the formation of the cavity itself. Facchini et al (2020) demonstrated that the appearance of one ring or multiple rings depends on the assumptions of the thermodynamics in hydrodynamical simulations where a planet is assumed to be embedded inside the cavity. Alternatively, low values of the disk viscosity, both in hydrodynamical simulations and dust evolution models, can change the appearance of the disk that is hosting a giant planet, spanning appearances that suggest a compact disk all the way to those suggesting multiple rings and gaps (e.g., de Juan Ovelar et al 2016;Bae et al 2018).…”

Puffed up Edges of Planet-opened Gaps in Protoplanetary Disks. I. hydrodynamic simulations

“…The origin of these rings are still being debated, although disk-planet interaction is frequently invoked (Dipierro et al 2015;Liu et al 2018;Muley et al 2019;Toci et al 2020;Pinte et al 2020). Here, a common approach is to first perform 2D disk-planet simulations, then construct a 3D dust distribution assuming a turbulent diffusion model (e.g., Equation 27; Dubrulle et al 1995), before producing a synthetic image via radiative transfer and comparing it with observations (e.g., Dong et al 2015;Jin et al 2016;Facchini et al 2020).…”