Evidence for Disk Photoevaporation Driven by the Central Star

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.

💡 Research Summary

The lifetime of protoplanetary disks is widely believed to be governed by a combination of viscous accretion, which transports material inward, and photoevaporation, in which high‑energy photons from the central star heat the disk surface and drive a thermal wind. While the accretion paradigm has been robustly confirmed through magnetospheric diagnostics, direct observational evidence for a star‑driven photoevaporative flow has remained elusive. In this paper the authors address this gap by obtaining high‑resolution (R ≈ 30 000) mid‑infrared spectra of the