# On the planetary interpretation of multiple gaps and rings in protoplanetary disks seen by ALMA

## TL;DR

This paper compares locally isothermal and adiabatic simulations of protoplanetary disks, showing that the common isothermal approximation overestimates ring contrast and misplaces features, affecting planet mass estimates from ALMA observations.

## Contribution

It demonstrates that the locally isothermal approximation can misrepresent density wave dynamics and ring features, emphasizing the need for energy-conserving simulations in planet-disk interaction studies.

## Key findings

- Locally isothermal simulations overestimate ring contrast.
- Isothermal approximation misplaces ring and gap features.
- Adiabatic simulations provide more accurate disk structures.

## Abstract

It has been recently suggested that the multiple concentric rings and gaps discovered by ALMA in many protoplanetary disks may be produced by a single planet, as a result of the complex propagation and dissipation of the multiple spiral density waves it excites in the disk. Numerical efforts to verify this idea have largely utilized the so-called locally isothermal approximation with a prescribed disk temperature profile. However, in protoplanetary disks this approximation does not provide an accurate description of the density wave dynamics on scales of tens of au. Moreover, we show that locally isothermal simulations tend to overestimate the contrast of ring and gap features, as well as misrepresent their positions, when compared to simulations in which the energy equation is evolved explicitly. This outcome is caused by the non-conservation of the angular momentum flux of linear perturbations in locally isothermal disks. We demonstrate this effect using simulations of locally isothermal and adiabatic disks (with essentially identical temperature profiles) and show how the dust distributions, probed by mm wavelength observations, differ between the two cases. Locally isothermal simulations may thus underestimate the masses of planets responsible for the formation of multiple gaps and rings on scales of tens of au observed by ALMA. We suggest that caution should be exercised in using the locally isothermal simulations to explore planet-disk interaction, as well as in other studies of wave-like phenomena in astrophysical disks.