Tracing High-Energy Radiation From T Tauri Stars Using Mid-Infrared Neon Emission From Disks

High-energy radiation from T Tauri stars (TTS) influences the amount and longevity of gas in disks, thereby playing a crucial role in the creation of gas giant planets. Here we probe the high-energy ionizing radiation from TTS using high-resolution mid-infrared (MIR) Spitzer Infrared Spectrograph neon forbidden line detections in a sample of disks from IC 348, NGC 2068, and Chamaeleon. We report three new detections of [Ne iii ] from CS Cha, SZ Cha, and T 54, doubling the known number of [Ne iii ] detections from TTS. Using [Ne iii ]-to-[Ne ii ] ratios in conjunction with X-ray emission measurements, we probe high-energy radiation from TTS. The majority of previously inferred [Ne iii ]/[Ne ii ] ratios based on [Ne iii ] line upper limits are significantly less than 1, pointing to the dominance of either X-ray radiation or soft extreme-ultraviolet (EUV) radiation in producing these lines. Here we report the first observational evidence for hard EUV-dominated Ne forbidden line production in a T Tauri disk: [Ne iii ]/[Ne ii ] ∼ 1 in SZ Cha. Our results provide a unique insight into the EUV emission from TTS, by suggesting that EUV radiation may dominate the creation of Ne forbidden lines, albeit in a minority of cases.