Connection between jets, winds and accretion in T Tauri stars: The X-shooter view

• Published in: Astronomy and astrophysics (Berlin) 2018-01, Vol.609, p.A87
• Main Authors: Nisini, B., Antoniucci, S., Alcalá, J. M., Giannini, T., Manara, C. F., Natta, A., Fedele, D., Biazzo, K.
• Format: Article
• Language: English
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361/201730834

Mass loss from jets and winds is a key ingredient in the evolution of accretion discs in young stars. While slow winds have been recently extensively studied in T Tauri stars, little investigation has been devoted on the occurrence of high velocity jets and on how the two mass-loss phenomena are connected with each other, and with the disc mass accretion rates. In this framework, we have analysed the [O  i ]6300 Å  line in a sample of 131 young stars with discs in the Lupus, Chamaeleon and σ Orionis star forming regions. The stars were observed with the X-shooter spectrograph at the Very Large Telescope and have mass accretion rates spanning from 10 -12 to 10 -7 M ⊙  yr -1 . The line profile was deconvolved into a low velocity component (LVC, | V r | < 40 km s -1 ) and a high velocity component (HVC, | V r | > 40 km s -1 ), originating from slow winds and high velocity jets, respectively. The LVC is by far the most frequent component, with a detection rate of 77%, while only 30% of sources have a HVC. The fraction of HVC detections slightly increases (i.e. 39%) in the sub-sample of stronger accretors (i.e. with log ( L acc / L ⊙ ) >−3). The [O  i ]6300 Å  luminosity of both the LVC and HVC, when detected, correlates with stellar and accretion parameters of the central sources (i.e. L ∗ , M ∗ , L acc , Ṁ acc ), with similar slopes for the two components. The line luminosity correlates better (i.e. has a lower dispersion) with the accretion luminosity than with the stellar luminosity or stellar mass. We suggest that accretion is the main drivers for the line excitation and that MHD disc-winds are at the origin of both components. In the sub-sample of Lupus sources observed with ALMA a relationship is found between the HVC peak velocity and the outer disc inclination angle, as expected if the HVC traces jets ejected perpendicularly to the disc plane. Mass ejection rates ( Ṁ jet ) measured from the detected HVC [O  i ]6300 Å  line luminosity span from ~10 -13 to ~10 -7 M ⊙  yr -1 . The corresponding Ṁ jet / Ṁ acc   ratio ranges from ~0.01 to ~0.5, with an average value of 0.07. However, considering the upper limits on the HVC, we infer a Ṁ jet / Ṁ acc   ratio < 0.03 in more than 40% of sources. We argue that most of these sources might lack the physical conditions needed for an efficient magneto-centrifugal acceleration in the star-disc interaction region. Systematic observations of populations of younger stars, that is, class 0/I, are needed to explore how th