An empirical criterion to classify T Tauri stars and substellar analogs using low-resolution spectroscopy

We have studied the H (equivalent widths and uxes) of late-type members of three young open clusters and used these data to dene a empirical criterion which allows, from the statistical point of view, to distinguish between Classical and Weak-line T Tauri stars. This criterion is based on the saturation of the chromospherical activity and can be used in combination with low resolution spectroscopy. We have extend this criterion into the substellar domain and apply it several star forming regions of dieren t ages. Our comparison shows that the fraction of accretor decline very fast with age both in the stellar and the substellar domain, becoming negligible at about 10 Myr.