GIARPS High-resolution Observations of T Tauri stars (GHOsT)

Abstract

This paper aims to revisit the kinematical and physical properties of the warm ($T 5000-10\ 000 K) atomic gas in the inner disk ($<5$ au) region of classical T Tauri stars (CTTs) and relate them to the properties of the outer dusty disk resolved with ALMA. We also want to define constraints for the mass-loss in the inner atomic winds and jets to assess their role in the evolution and dispersal of planet-forming disks. We used the high resolution (R=115,000, sim 2.6 spectra of 36 CTTs observed as part of the GIARPS High-resolution Observations of T Tauri stars (GHOsT) project and analysed the profile and luminosity of the brightest optical forbidden lines, namely and We decomposed the line profiles into different velocity components, and concentrated our analysis mostly on the so-called narrow low-velocity component (NLVC). We find that about 40 $<!PCT!>$ of sources display a NLVC peak velocity (V$_p$) compatible with the stellar velocity. These include the transitional disks (TD) and typically show a single low velocity component (LVC), lower mass accretion rates, and the absence of a jet. They therefore might represent later evolutionary stages where the emission from the disk is dominant with respect to the wind contribution. No difference in kinematical properties was instead found between sources with full disks and disks with substructures as resolved by ALMA. The profiles peaking at the stellar velocity are well fitted by a simple Keplerian disk model, where the emission line region extends from sim 0.01 au up to several tens of au in some cases. The emission is detected inside the sub-millimetre dust cavities of all the TDs. No correlation is found between kep $, derived from the line half width at half maximum (HWHM), and the size of the dust cavity. We see an anti-correlation between the 557/630 nm ratio and kep $, which suggests that the emitting region expands as the gas dominating the emission cools and becomes less dense. We confirmed previous findings that the line ratios observed in the LVC, if compared with a thermal single temperature and density model, imply $n_e and $T_e 5000 - 10\,000 K, and additionally constrained the ionisation fraction in the NLVC to be $x_e < 0.1$. We however discuss the limits of applying this diagnostic to winds that are not spatially resolved. The emission from the disk should be considered as an important contribution to the forbidden line emission in CTTs. Also, the clearing of warm atomic gas from the upper disk layers does not seem to follow the dispersal of the bulk of molecular gas and dust during late disk evolution. For the outflow component, we estimated the mass-loss for both the disk winds and jets. We conclude that without better knowledge of the wind geometry and spatial extent, and given the limitation of the diagnostics, the mass-loss rates in the wind traced by the blue shifted LVC cannot be constrained better than a factor of 100, with a spanning between sim 0.01 and more than 1. When compared with synthetic images of X-ray photoevaporation models, the estimated represents a lower limit to the total mass-loss rate of the model, indicating that is likely not the best tracer to probe mass-loss in low-velocity winds.