Accretion properties of T Tauri stars in sigma Ori

TL;DR

This study investigates the accretion properties of young stars in sigma Ori, revealing lower accretion rates compared to younger regions and demonstrating the utility of He I lines as accretion indicators in low accretors.

Contribution

It provides new measurements of accretion rates in sigma Ori and highlights the effectiveness of He I lines as indicators in very low accretors.

Findings

Accretion rates are lower in sigma Ori than in younger regions.

He I 1.083 micron line detects accretion activity in very low accretors.

He I line is present in 72% of disk-bearing stars.

Abstract

Accretion disks around young stars evolve in time with time scales of few million years. We present here a study of the accretion properties of a sample of 35 stars in the ~3 million year old star-forming region sigma Ori. Of these, 31 are objects with evidence of disks, based on their IR excess emission. We use near-IR hydrogen recombination lines (Pa_gamma) to measure their mass accretion rate. We find that the accretion rates are significantly lower in sigma Ori than in younger regions, such as rho-Oph, consistently with viscous disk evolution. The He I 1.083 micron line is detected (either in absorption or in emission) in 72% of the stars with disks, providing evidence of accretion-powered activity also in very low accretors, where other accretion indicators dissapear.