Episodic disk accretion in the halo of the 'old' Pre-Main Sequence cluster Eta Chamaeleontis

TL;DR

This study reports episodic disk accretion in old pre-main sequence stars in Eta Chamaeleontis, revealing that accretion activity can be intermittent and often missed in surveys, affecting estimates of disk dissipation times.

Contribution

First detection of episodic accretion in old pre-main sequence stars in the Eta Chamaeleontis cluster, highlighting the variability and incompleteness of accretion surveys.

Findings

Detected episodic accretion events with variable H-alpha profiles.

Derived accretion rates of ~10^-8.7 Msun/yr during activity.

Showed that accretion episodes can last days to months.

Abstract

We present multi-epoch medium-resolution observations of two M4.5 candidate members in the halo of the ~8 Myr Eta Chamaeleontis open cluster. Over six months of observations both stars exhibited variations in their H-alpha line profiles on timescales of days to months, with at least one episode of substantial activity attributable to accretion from a circumstellar disk. We derive an accretion rate ~10^-8.7 Msun/yr for this event, with a rate of ~10^-10.6 Msun/yr in quiescence. Episodic accretion like that observed here means existing surveys of accreting Weak-lined T-Tauri Stars in young clusters are likely incomplete and that gas dissipation timescales calculated from the fraction of accreting objects are underestimates.