Evolution of X-ray and FUV Disk-Dispersing Radiation Fields

TL;DR

This study provides new observational data on X-ray and FUV radiation from T Tauri stars across a wide age range, confirming their roles in disk dispersal and assessing the evolution of high-energy radiation fields.

Contribution

It offers the first observational evidence for FUV radiation evolution in young stars and compares high-energy radiation levels with photoevaporation models for disk dissipation.

Findings

X-ray emission remains constant from 1 to 10 Myr.

FUV radiation decreases with stellar age, aligning with accretion decline.

High-energy radiation levels are consistent with disk dispersal timescales of ~10 Myr.

Abstract

We present new X-ray and Far Ultraviolet (FUV) observations of T Tauri stars covering the age range 1 to 10 Myr. Our goals are to observationally constrain the intensity of radiation fields responsible for evaporating gas from the circumstellar disk and to assess the feasibility of current photoevaporation models, focusing on X-ray and UV radiation. We greatly increase the number of 7-10 Myr old T Tauri stars observed in the X-rays by including observations of the well populated 25 Ori aggregate in the Orion OB1a subassociation. With these new 7-10 Myr objects, we confirm that X-ray emission remains constant from 1-10 Myr. We also show, for the first time, observational evidence for the evolution of FUV radiation fields with a sample of 56 accreting and non-accreting young stars spanning 1 Myr to 1 Gyr. We find that the FUV emission decreases on timescales consistent with the decline of accretion in classical T Tauri stars until reaching the chromospheric level in weak T Tauri stars and debris disks. Overall, we find that the observed strength of high energy radiation is consistent with that required by photoevaporation models to dissipate the disks in timescales of approximately 10 Myr. Finally, we find that the high energy fields that affect gas evolution are not similarly affecting dust evolution; in particular, we find that disks with inner clearings, the transitional disks, have similar levels of FUV emission as full disks.