Discovery of an old photoevaporating disk in σ Orionis

The photoevaporation of circumstellar disks is a powerful process in the disk dissipation at the origin of the Orion proplyds. This Letter reports the first detection of a photoevaporating disk in the final but long-lasting phase of its evolution. The disk is associated to a low-mass T Tauri member of the σ Ori Cluster. It is characterized by a very low (if any) accretion rate and by a tenuous (dot M_loss ∼ 10^-9 M_⊙/yr) photoevaporation wind, which is unambiguously detected in the optical spectrum of the object. The wind emits strong forbidden lines of [SII] and [NII] because the low-mass star is close to a powerful source of ionizing photons, the O9.5 star σ Ori.

Based on observations collected at the European Southern Observatory, Chile. Program 074.D-0136(A).