What is the Mass of a Gap-Opening Planet?

TL;DR

This study develops a method to estimate the masses of planets opening gaps in protoplanetary disks by analyzing observed gap properties through hydrodynamics and radiative transfer simulations, providing a way to infer planet characteristics from disk images.

Contribution

It introduces a quantitative approach linking observed gap features to planet mass and disk properties, improving planet mass estimates from disk observations.

Findings

Derived correlations between gas surface density gaps and observed disk gaps.

Estimated planet masses in observed disks are roughly between 0.1-1 Jupiter masses.

Provided a method to constrain disk scale height and planet mass using imaging data.

Abstract

High contrast imaging instruments such as GPI and SPHERE are discovering gap structures in protoplanetary disks at an ever faster pace. Some of these gaps may be opened by planets forming in the disks. In order to constrain planet formation models using disk observations, it is crucial to find a robust way to quantitatively back out the properties of the gap-opening planets, in particular their masses, from the observed gap properties, such as their depths and widths. Combing 2D and 3D hydrodynamics simulations with 3D radiative transfer simulations, we investigate the morphology of planet-opened gaps in near-infrared scattered light images. Quantitatively, we obtain correlations that directly link intrinsic gap depths and widths in the gas surface density to observed depths and widths in images of disks at modest inclinations under finite angular resolution. Subsequently, the properties of the surface density gaps enable us to derive the disk scale height at the location of the gap $h$, and to constrain the quantity $M_{\rm p}^2/\alpha$, where $M_{\rm p}$ is the mass of the gap-opening planet and $\alpha$ characterizes the viscosity in the gap. As examples, we examine the gaps recently imaged by VLT/SPHERE, Gemini/GPI, and Subaru/HiCIAO in HD 97048, TW Hya, HD 169142, LkCa 15, and RX J1615.3-3255. Scale heights of the disks and possible masses of the gap-opening planets are derived assuming each gap is opened by a single planet. Assuming $\alpha=10^{-3}$, the derived planet mass in all cases are roughly between 0.1-1 $M_{\rm J}$.