X-shooter spectroscopy of young stellar objects

V. Slow winds in T Tauri stars^⋆,⋆⋆

¹ INAF/Osservatorio Astrofisico of Arcetri, Largo E. Fermi, 5, 50125 Firenze, Italy
e-mail: natta@arcetri.astro.it
² School of Cosmic Physics, Dublin Institute for Advanced Studies, 31 Fitzwilliams Place, 2 Dublin, Ireland
³ ESO/European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
⁴ INAF/Osservatorio Astronomico di Capodimonte, Salita Moiariello, 16 80131 Napoli, Italy
⁵ Department of Planetary Science, Lunar and Planetary Lab, University of Arizona, 1629, E. University Blvd, 85719, Tucson, AZ, USA
⁶ INAF/Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
⁷ ASI-Science Data Center, via del Politecnico snc, 00133 Rome, Italy

Received: 5 May 2014
Accepted: 13 June 2014

Abstract

Disks around T Tauri stars are known to lose mass, as best shown by the profiles of the forbidden emission lines of low-ionization species. At least two separate kinematic components have been identified, one characterized by velocity shifts of tens to hundreds of km s^-1 (HVC) and one with a much lower velocity of a few km s^-1 (LVC). The HVC are convincingly associated to the emission of jets, but the origin of the LVC is still unknown. In this paper we analyze the forbidden line spectrum of a sample of 44 mostly low-mass young stars in Lupus and σ Ori observed with the X-shooter ESO spectrometer. We detect forbidden line emission of O i, O ii, S ii, N i, and N ii, and characterize the line profiles as LVC, blueshifted HVC, and redshifted HVC. We focus our study on the LVC. We show that there is a good correlation between line luminosity and both L_star and the accretion luminosity (or the mass accretion rate) over a large interval of values (L_star~ 10^-2−1 L_⊙; L_acc~ 10^-5−10^-1 L_⊙; Ṁ_acc~ 10^-11 − 10^-7 M_⊙/yr). The lines show the presence of a slow wind (V_peak< 20 km s^-1) that is dense (n_H> 10⁸ cm^-3), warm (T ~ 5000−10 000 K), mostly neutral. We estimate the mass of the emitting gas and provide a value for the maximum volume it occupies. Both quantities increase steeply with the stellar mass, from ~ 10^-12 M_⊙ and ~0.01 AU³ for M_star~ 0.1 M_⊙, to ~ 3 × 10^-10 M_⊙ and ~1 AU³ for M_star~ 1 M_⊙, respectively. These results provide quite stringent constraints to wind models in low-mass young stars, that need to be explored further.