We present X-Shooter/VLT observations of a sample of 36 accreting low-mass stellar and sub-stellar objects ( YSOs ) in the Lupus star forming region , spanning a range in mass from \sim 0.03 to \sim 1.2 M _ { \odot } , but mostly with 0.1 M _ { \odot } < M _ { \star } < 0.5 M _ { \odot } .
Our aim is twofold : firstly , analyse the relationship between excess-continuum and line emission accretion diagnostics , and , secondly , to investigate the accretion properties in terms of the physical properties of the central object .
The accretion luminosity ( L _ { acc } ) , and from it the accretion rate ( \dot { M } _ { acc } ) , is derived by modelling the excess emission , from the UV to the near-IR , as the continuum emission of a slab of hydrogen .
The flux and luminosity ( L _ { line } ) of a large number of emission lines of { H \textsc { } } , { He \textsc { } } , { Ca \textsc { ii } } , etc. , observed simultaneously in the range from \sim 330 nm to 2500 nm , were computed .
The luminosity of all the lines is well correlated with L _ { acc } .
We provide empirical relationships between L _ { acc } and the luminosity of 39 emission lines , which have a lower dispersion as compared to previous relationships in the literature .
Our measurements extend the Pa \beta and Br \gamma relationships to L _ { acc } values about two orders of magnitude lower than those reported in previous studies .
We confirm that different methodologies to measure L _ { acc } and \dot { M } _ { acc } yield significantly different results : H \alpha line profile modelling may underestimate \dot { M } _ { acc } by 0.6 to 0.8 dex with respect to \dot { M } _ { acc } derived from continuum-excess measures .
Such differences may explain the likely spurious bi-modal relationships between \dot { M } _ { acc } and other YSOs properties reported in the literature .
We derive \dot { M } _ { acc } in the range 2 \times 10 ^ { -12 } – 4 \times 10 ^ { -8 } M _ { \odot } yr ^ { -1 } and conclude that \dot { M } _ { acc } \propto M _ { \star } ^ { 1.8 ( \pm 0.2 ) } , with a dispersion lower by a factor of about 2 than in previous studies .
A number of properties indicate that the physical conditions of the accreting gas are similar over more than 5 orders of magnitude in \dot { M } _ { acc } , confirming previous suggestions that it is the geometry of the accretion flow that controls the rate at which the disc material accretes onto the central star .