Detection of H$_2$ in the TWA 7 System: A Probable Circumstellar Origin

TL;DR

This study reports the detection of warm molecular hydrogen around the 9-million-year-old star TWA 7, suggesting the presence of circumstellar gas in a system previously thought to lack accretion activity.

Contribution

First detection of warm molecular hydrogen in the TWA 7 debris disk indicating possible ongoing low-level accretion and circumstellar gas presence.

Findings

Detection of molecular hydrogen via HST-COS FUV spectra.

Evidence suggests the hydrogen is circumstellar, not stellar.

TWA 7 may still retain a gas reservoir despite being a debris disk.

Abstract

Using HST-COS FUV spectra, we have discovered warm molecular hydrogen in the TWA 7 system. TWA 7, a $\sim$9 Myr old M2.5 star, has a cold debris disk and has previously shown no signs of accretion. Molecular hydrogen is expected to be extremely rare in a debris disk. While molecular hydrogen can be produced in star spots or the lower chromospheres of cool stars such as TWA 7, fluxes from progressions that get pumped by the wings of Ly$\alpha$ indicate that this molecular hydrogen could be circumstellar and thus that TWA 7 is accreting at very low levels and may retain a reservoir of gas in the near circumstellar environment.