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

TL;DR

This study uses mid-infrared Neon emission lines to investigate the high-energy radiation from T Tauri stars, revealing evidence for EUV radiation's role in ionizing disk gas and its implications for planet formation.

Contribution

It provides the first observational evidence for EUV-dominated Neon line production in T Tauri disks, expanding understanding of stellar radiation influence.

Findings

Detection of three new [Ne III] lines in T Tauri disks.

[Ne III]/[Ne II] ratio ~1 in SZ Cha indicates EUV dominance.

Most ratios suggest X-ray or soft EUV radiation as primary ionizers.

Abstract

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 IRS 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.