Observational Signatures of Planets in Protoplanetary Disks I: Gaps Opened by Single and Multiple Young Planets in Disks

TL;DR

This study combines hydrodynamical and radiative transfer simulations to analyze how planets create observable gaps in protoplanetary disks, supporting the planet-origin hypothesis for transitional disk features.

Contribution

It provides detailed modeling of gap formation by single and multiple planets and compares simulated signatures with observations, advancing understanding of disk-planet interactions.

Findings

Single 0.2 MJ planets can produce deep mm gaps with minimal NIR features.

Multiple planets can create wide common gaps at both mm and NIR wavelengths.

NIR gap sizes are often smaller than mm gaps due to dust-gas coupling.

Abstract

It has been suggested that the gaps and cavities recently discovered in transitional disks are opened by planets. To explore this scenario, we combine two-dimensional two fluid (gas + particle) hydrodynamical calculations with three-dimensional Monte Carlo Radiative Transfer simulations, and study the observational signatures of gaps opened by one or several planets, making qualitative comparisons with observations. We find that a single planet as small as 0.2 MJ can produce a deep gap at millimeter (mm) wavelengths and almost no features at near-infrared (NIR) wavelengths, while multiple planets can open up a few *10 AU wide common gap at both wavelengths. Both the contrast ratio of the gaps and the wavelength dependence of the gap sizes are broadly consistent with data. We also confirm previous results that NIR gap sizes may be smaller than mm gap sizes due to dust-gas coupling and radiative transfer effects. When viewed at a moderate inclination angle, a physically circular on-centered gap could appear to be off-centered from the star due to shadowing. Planet-induced spiral arms are more apparent at NIR than at mm wavelengths. Overall, our results suggest that the planet-opening-gap scenario is a promising way to explain the origin of the transitional disks. Finally, inspired by the recent ALMA release of the image of the HL Tau disk, we show that multiple narrow gaps, well separated by bright rings, can be opened by 0.2 MJ planets soon after their formation in a relatively massive disk.