# Using Multiwavelength Variability to Explore the Connection between X-ray Emission, the Far-Ultraviolet H2 Bump, and Accretion in T Tauri Stars

## TL;DR

This study investigates the relationship between X-ray emission, UV features, and accretion in T Tauri stars using multiwavelength observations, revealing correlations with accretion but no direct link to X-ray effects on the inner disk.

## Contribution

It provides new observational evidence on the connection between X-ray activity, UV emission, and accretion processes in T Tauri stars through coordinated multiwavelength data.

## Key findings

- No correlation between FUV H2 bump and X-ray luminosity.
- Correlation between FUV H2 bump and accretion luminosity.
- X-ray luminosity correlates with accretion column density.

## Abstract

The high-energy radiation fields of T Tauri stars (TTS) should affect the surrounding circumstellar disk, having implications for disk transport and heating. Yet, observational evidence of the effect of high-energy fields on disks is scarce. Here we investigate the connection between X-ray emission and the innermost gas disk by leveraging the variability of TTS. We obtained multiple epochs of coordinated data (taken either simultaneously or within a few hours) of accreting TTS with the Hubble Space Telescope, the Neil Gehrels Swift Observatory, and the Chandra X-ray Observatory. We measured the far-ultraviolet (FUV) H2 bump feature at 1600 A, which traces gas <1 AU from the star; the near-ultraviolet (NUV) emission, from which we extract the accretion luminosity; and also the X-ray luminosity. We do not find a correlation between the FUV H2 bump and X-ray luminosity. Therefore, an observable tracer of the effect of X-ray ionization in the innermost disk remains elusive. We report a correlation between the FUV H2 bump and accretion luminosity, linking this feature to the disk surface density. We also see a correlation between the X-ray luminosity and the accretion column density, implying that flaring activity may influence accretion. These results stress the importance of coordinated multiwavelength work to understand TTS.