The Periastron Passage of T Tauri South B as Viewed by ALMA: Millimeter Flux Variations and Dust Heating Triggered by Orbital Motion

TL;DR

This study uses ALMA observations to analyze millimeter flux variations and dust heating in the T Tauri system during the recent periastron passage of T Tau Sb, revealing dynamic changes in dust emission and potential magnetic interactions.

Contribution

First detailed ALMA imaging of T Tauri during periastron, showing flux increases, dust heating, and morphological changes linked to orbital motion.

Findings

Increased millimeter flux from dust heating during periastron

Morphological changes in dust emission around the binary

Detection of a moving crescent-shaped dust structure around T Tau N

Abstract

We present 225 and 350 GHz imaging of the iconic T Tauri system using the Atacama Large Millimeter submillimeter Array (ALMA). T Tauri is a hierarchical triple system, and the close binary T Tau Sa/Sb underwent periastron passage in March 2023. The ALMA images were obtained in epochs spanning November 2019 through June 2023, and therefore covered the time frame of the recent periastron passage. We clearly resolve the Sa-Sb binary in two epochs of high-resolution measurements with ALMA. We find increases in millimeter flux from heating of the Sa disk and the wider distribution of dust in the environment of the binary. This heating is likely in response to increased stellar accretion activity triggered by orbital motion during the dynamic periastron passage of T Tau Sb around Sa. Resolved, extended millimeter emission is also found to change morphology and increase in flux in the immediate environment of the Sa-Sb binary after periastron passage. This may suggest an increase in nonthermal emission from magnetic interaction, gravitational disruption of the circumstellar disks as the stars passed through periastron, or both of these phenomena. We also detected structures in the compact (24 au radius), thermal dust disk around T Tau N. In particular, we identify a crescent-shaped emission excess just outside a shallow gap at 12 au radius that appears to move at Keplerian speed. Future measurement of dust spectral indices can clarify the origin of increased and variable millimeter emission in the environment of the T Tau S binary.