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 ] 6300Å line in a sample of 131 young stars with discs in the Lupus , Chamaeleon and \sigma Orionis star forming regions .
The stars were observed with the X-shooter spectrograph at the Very Large Telescope ( VLT ) and have mass accretion rates spanning from 10 ^ { -12 } to 10 ^ { -7 } M _ { \odot } yr ^ { -1 } .
The line profile was deconvolved into a low velocity component ( LVC , —V _ { r } — < 40km s ^ { -1 } ) and a high velocity component ( HVC , —V _ { r } — > 40km 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 _ { \mathrm { acc } } /L _ { \odot } ) > - 3 ) .
The [ O i ] 6300Å luminosity of both the LVC and HVC , when detected , correlates with stellar and accretion parameters of the central sources ( i.e . L _ { \mathrm { * } } , M _ { \mathrm { * } } , L _ { \mathrm { acc } } , \dot { M } _ { 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 ( \dot { M } _ { jet } ) measured from the detected HVC [ O i ] 6300Å line luminosity span from \sim 10 ^ { -13 } to \sim 10 ^ { -7 } M _ { \odot } yr ^ { -1 } .
The corresponding \dot { M } _ { jet } / \dot { M } _ { acc } ratio ranges from \sim 0.01 to \sim 0.5 , with an average value of 0.07 .
However , considering the upper limits on the HVC , we infer a \dot { M } _ { jet } / \dot { M } _ { 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 the frequency and role of jets evolve during the pre-main sequence phase .
This will be possible in the near future thanks to space facilities such as the James Webb space telescope ( JWST ) .