Magnetic-field measurements of T Tauri stars in the Orion Nebula cluster

TL;DR

This study measures strong magnetic fields in T Tauri stars within the Orion Nebula, revealing that magnetic pressure dominates their photospheres and declines with age, which may explain their X-ray emission levels.

Contribution

First high-resolution infrared spectroscopic measurements of magnetic fields in Orion T Tauri stars, showing surface magnetic coverage and its evolution over time.

Findings

Kilogauss magnetic fields detected in Orion T Tauri stars.

Magnetic pressure likely dominates over gas pressure in stellar photospheres.

Magnetic flux decreases steadily with stellar age.

Abstract

We present an analysis of high-resolution ($R \sim 50,000$) infrared K-band echelle spectra of 14 T Tauri stars in the Orion Nebula Cluster. We model Zeeman broadening in three magnetically sensitive \ion{Ti}{1} lines near $2.2\ \mu$m and consistently detect kilogauss-level magnetic fields in the stellar photospheres. The data are consistent in each case with the entire stellar surface being covered with magnetic fields, suggesting that magnetic pressure likely dominates over gas pressure in the photospheres of these stars. These very strong magnetic fields might themselves be responsible for the underproduction of X-ray emission of T Tauri stars relative to what is expected based on main-sequence star calibrations. We combine these results with previous measurements of 14 stars in Taurus and 5 stars in the TW Hydrae association to study the potential variation of magnetic-field properties during the first 10 million years of stellar evolution, finding a steady decline in total magnetic flux with age.