EDP Sciences
Free Access
Volume 481, Number 2, April II 2008
Page(s) 423 - 432
Section Interstellar and circumstellar matter
DOI https://doi.org/10.1051/0004-6361:20078971
Published online 07 February 2008

A&A 481, 423-432 (2008)
DOI: 10.1051/0004-6361:20078971

Accretion properties of T Tauri stars in $\sigma$ Orionis

T. Gatti1, 2, A. Natta1, S. Randich1, L. Testi1, 3, and G. Sacco4

1  Osservatorio Astrofisico di Arcetri, INAF, Largo E. Fermi 5, 50125 Firenze, Italy
    e-mail: natta@arcetri.astro.it
2  Università di Firenze, Dipartimento di Astronomia, Largo E. Fermi 5, 50125 Firenze, Italy
3  ESO, Karl-Schwarschild Strasse 2, 85748 Garching bei München, Germany
4  Osservatorio Astronomico di Palermo, INAF, Piazza del Parlamento 1, 90134 Palermo, Italy

(Received 31 October 2007 / Accepted 16 January 2008)

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 $\sim $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.

Key words: stars: formation -- accretion, accretion disks

© ESO 2008