# An Inner Disk in the Large Gap of the Transition Disk SR 24S

## TL;DR

This study uses high-resolution ALMA observations at 2.75 mm to reveal an inner disk within the large gap of the SR 24S transition disk, supporting the planet formation scenario over other mechanisms.

## Contribution

It provides the first detailed analysis of the inner disk at 2.75 mm and constrains the properties of potential planets responsible for the disk's gap.

## Key findings

- Detection of an inner disk at 2.75 mm within the large gap.
- Photoevaporation and dead zone mechanisms are unlikely to explain the cavity.
- Constraints on planet mass and disk viscosity suggest a single planet of less than 5 Jupiter masses.

## Abstract

We report new Atacama Large Millimeter/sub-millimeter Array (ALMA) Band 3 observations at 2.75 mm of the TD around SR 24S with an angular resolution of $\sim$0.11''$\times$ 0.09'' and a peak signal-to-noise ratio of $\sim24$. We detect an inner disk and a mostly symmetric ring-like structure that peaks at $\sim$0.32'', that is $\sim$37 au at a distance of $\sim$114.4 pc. The full width at half maximum of this ring is $\sim$28 au. We analyze the observed structures by fitting the dust continuum visibilities using different models for the intensity profile, and compare with previous ALMA observations of the same disk at 0.45 mm and 1.30 mm. We qualitatively compare the results of these fits with theoretical predictions of different scenarios for the formation of a cavity or large gap. The comparison of the dust continuum structure between different ALMA bands indicates that photoevaporation and dead zone can be excluded as leading mechanisms for the cavity formation in SR 24S disk, leaving the planet scenario (single or multiple planets) as the most plausible mechanism. We compared the 2.75 mm emission with published (sub-)centimeter data and find that the inner disk is likely tracing dust thermal emission. This implies that any companion in the system should allow dust to move inwards throughout the gap and replenish the inner disk. In the case of one single planet, this puts strong constraints on the mass of the potential planet inside the cavity and the disk viscosity of about $\lesssim$5 $M_{\rm{Jup}}$ and $\alpha\sim10^{-4}-10^{-3}$, respectively.