GIARPS High-resolution Observations of T Tauri stars (GHOsT). I. Jet
  line emission
  The mechanism for jet formation in the disks of T Tauri stars is poorly
understood. Observational benchmarks to launching models can be provided by
tracing the physical properties of the kinematic components of the wind and jet
in the inner 100 au of the disk surface. In the framework of the GHOsT (GIARPS
High-resolution Observations of T Tauri stars) project, we aim to perform a
multi-line analysis of the velocity components of the gas in the jet
acceleration zone. We analyzed the GIARPS-TNG spectra of six objects in the
Taurus-Auriga complex (RY Tau, DG Tau, DL Tau, HN Tau, DO Tau, RW Aur A).
Thanks to the combined high-spectral resolution (R=50000-115000) and wide
spectral coverage (~400-2400 nm) we observed several O, S+, N, N+, and Fe+
forbidden lines spanning a large range of excitation and ionization conditions.
In four objects (DG Tau, HN Tau, DO Tau, RW Aur A), temperature (T_e), electron
and total density (n_e, n_H), and fractional ionization (x_e) were derived as a
function of velocity through an excitation and ionization model. The abundance
of gaseous iron, X(Fe), a probe of the dust content in the jet, was derived in
selected velocity channels. The physical parameters vary smoothly with
velocity, suggesting a common origin for the different kinematic components. In
DG Tau and HN Tau, T_e, x_e, and X(Fe) increase with velocity (roughly from
6000 K, 0.05, 10% X(Fe)_sun to 15000 K, 0.6, 90% X(Fe)_sun). This trend is in
agreement with disk-wind models in which the jet is launched from regions of
the disk at different radii. In DO Tau and RW Aur A, we infer x_e < 0.1, n_H
~10^6-7 cm^-3, and X(Fe) <~ X(Fe)_sun at all velocities. These findings are
tentatively explained by the formation of these jets from dense regions inside
the inner, gaseous disk, or as a consequence of their high degree of
collimation.
