The Masses of Transition Circumstellar Disks: Observational Support for Photoevaporation Models

TL;DR

This study uses sub-millimeter observations and spectral energy distributions to show that outer disks around pre-main-sequence stars are depleted before inner disks, supporting photoevaporation as a key disk dispersal mechanism.

Contribution

It provides observational evidence linking outer disk mass depletion to inner disk dissipation, supporting photoevaporation models of disk evolution.

Findings

Outer disks are often depleted before inner disks dissipate.

High mid-IR excess correlates with detectable disk mass.

Inner disks start to dissipate after significant outer disk depletion.

Abstract

We report deep Sub-Millimeter Array observations of 26 pre-main-sequence (PMS) stars with evolved inner disks. These observations measure the mass of the outer disk (r ~20-100 AU) across every stage of the dissipation of the inner disk (r < 10 AU) as determined by the IR spectral energy distributions (SEDs). We find that only targets with high mid-IR excesses are detected and have disk masses in the 1-5 M_Jup range, while most of our objects remain undetected to sensitivity levels of M_DISK ~0.2-1.5 M_Jup. To put these results in a more general context, we collected publicly available data to construct the optical to millimeter wavelength SEDs of over 120 additional PMS stars. We find that the near-IR and mid-IR emission remain optically thick in objects whose disk masses span 2 orders of magnitude (~0.5-50 M_Jup). Taken together, these results imply that, in general, inner disks start to dissipate only after the outer disk has been significantly depleted of mass. This provides strong support for photoevaporation being one of the dominant processes driving disk evolution.