  A homogeneous determination of basic stellar parameters of young stellar
object (YSO) candidates is needed to confirm their evolutionary stage,
membership to star forming regions (SFRs), and to get reliable values of the
quantities related to chromospheric activity and accretion. We used the code
ROTFIT and synthetic BT-Settl spectra for the determination of the atmospheric
parameters (Teff and logg), the veiling, the radial (RV) and projected
rotational velocity (vsini), from X-Shooter spectra of 102 YSO candidates in
the Lupus SFR. We have shown that 13 candidates can be rejected as Lupus
members based on their discrepant RV with respect to Lupus and/or the very low
logg values. At least 11 of them are background giants. The spectral
subtraction of inactive templates enabled us to measure the line fluxes for
several diagnostics of both chromospheric activity and accretion. We found that
all Class-III sources have H$\alpha$ fluxes compatible with a pure
chromospheric activity, while objects with disks lie mostly above the boundary
between chromospheres and accretion. YSOs with transitional disks displays both
high and low H$\alpha$ fluxes. We found that the line fluxes per unit surface
are tightly correlated with the accretion luminosity ($L_{\rm acc}$) derived
from the Balmer continuum excess. This rules out that the relationships between
$L_{\rm acc}$ and line luminosities found in previous works are simply due to
calibration effects. We also found that the CaII-IRT flux ratio,
$F_{8542}/F_{8498}$, is always small, indicating an optically thick emission
source. The latter can be identified with the accretion shock near the stellar
photosphere. The Balmer decrement reaches instead, for several accretors, high
values typical of optically thin emission, suggesting that the Balmer emission
originates in different parts of the accretion funnels with a smaller optical
depth.
