Time-Variable Accretion in the TW Hya Star/Disk System

TL;DR

This study reports variable accretion rates in TW Hya based on near-infrared spectroscopy, revealing episodic accretion events with minimal dust in the inner disk, challenging previous estimates.

Contribution

First direct measurement of accretion variability in TW Hya using high-dispersion near-IR spectra, highlighting episodic accretion with low dust content in the inner disk.

Findings

Accretion rate is higher than previously estimated.

Accretion exhibits variability across observed epochs.

Inner disk shows minimal dust despite accretion variability.

Abstract

We present two epochs of observations of TW Hya from the high-dispersion near-IR spectrograph ARIES at the MMT. We detect strong emission from the Brackett gamma transition of hydrogen, indicating an accretion rate substantially larger than previously estimated using hydrogen line emission. The Brackett gamma line-strength varies across our two observed epochs. We also measure circumstellar-to-stellar flux ratios (i.e., veilings) that appear close to zero in both epochs. These findings suggest that TW Hya experiences episodes of enhanced accretion while the inner disk remains largely devoid of dust. We discuss several physical mechanisms that may explain these observations.