Evidence for Disk Photoevaporation Driven by the Central Star

TL;DR

This study provides the first observational evidence that stellar extreme UV photons drive photoevaporative winds in protoplanetary disks, especially in transition disks, influencing their evolution and dispersal.

Contribution

It presents high-resolution spectroscopic evidence linking stellar UV-driven photoevaporation to disk dispersal, particularly in transition disks, advancing understanding of disk evolution mechanisms.

Findings

[NeII] line profiles indicate photoevaporative winds in transition disks.

No [NeII] emission detected from non-transition disks, suggesting different origins.

Extreme UV photoevaporation likely occurs at later stages of disk evolution.

Abstract

The lifetime of isolated protoplanetary disks is thought to be set by the combination of viscous accretion and photoevaporation driven by stellar high-energy photons. Observational evidence for magnetospheric accretion in young sun-like stars is robust. Here we report the first observational evidence for disk photoevaporation driven by the central star. We acquired high-resolution (R~30,000) spectra of the [NeII] 12.81 micron line from 7 circumstellar disks using VISIR on Melipal/VLT. We show that the 3 transition disks in the sample all have [NeII] line profiles consistent with those predicted by a photoevaporative flow driven by stellar extreme UV photons. The ~6 km/s blue-shift of the line from the almost face-on disk of TW Hya is clearly inconsistent with emission from a static disk atmosphere and convincingly points to the presence of a photoevaporative wind. We do not detect any [NeII] line close to the stellar velocity from the sample of classical optically thick (non-transition) disks. We conclude that most of the spectrally unresolved [NeII] emission in these less evolved systems arises from jets/outflows rather than from the disk. The pattern of the [NeII] detections and non-detections suggests that extreme UV-driven photoevaporation starts only at a later stage in the disk evolution.