Accretion properties of T Tauri stars in σ Orionis

Accretion disks around young stars evolve in time with time scales of a few million years. We present here a study of the accretion properties of a sample of 35 stars in the similar to 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 significant lower in sigma Ori than in younger regions, such as rho Oph, consistently with viscous disk evolution. The He I 1.083 mu m line is detected (either in absorption or in emission) in 72% of the stars with disks, also providing evidence of accretion-powered activity in very low accretors, where other accretion indicators disappear.