Helium emission from classical T Tauri stars: Dual origin in magnetospheric infall and hot wind

High-resolution emission-line profiles of He I and He II in 31 classical T Tauri stars are analyzed with the aim of probing the environs of the star-d isk interface in accreting low-mass young stars. The diagnostic power of th e helium lines lies in their high-excitation potentials, which restrict the ir formation to a region either of high temperature or close proximity to a source of ionizing radiation. The He I profiles are decomposed into kinema tic components that support the paradigm of magnetically controlled accreti on from the disk onto the stellar surface but also require a significant co ntribution from a hot wind. A narrow component, seen in 28/31 stars, is cha racterized by relatively uniform line widths and centroid velocities among all the helium lines. Our analysis supports previous conclusions that this feature is consistent with formation in the decelerating postshock gas at t he magnetosphere footpoint. A broad component, seen in 22/31 stars, display s a diversity of kinematic properties. Our analysis suggests that in many s tars the He I broad component is itself composite. At one extreme are stars where the broad component is redshifted in excess of 8 km s(-1), as would occur if helium emission arises primarily from polar angles less than in th e funnel flow. At the other extreme are stars where the broad component 54. degrees7 is blueshifted in excess of -30 km s(-1), requiring an origin in o utflowing gas. The additional occurrence of maximum blue wing velocities ex ceeding -200 km s(-1) in 14 stars leads us to argue that hot winds are pres ent in about half of our sample. The relation between the narrow component and the optical veiling differs between the stars with or without a hot hel ium wind, suggesting that when the hot wind is present the luminosity and t emperature of the accretion shock are reduced. A comparison of broad compon ent helium emission with standard outflow indicators leads us to suggest th at there are two sources of inner wind in T Tauri accretion disk systems: o ne a hot polar/coronal wind that prevails in stars with high veiling, and t he other a more widespread cool disk wind that is likely launched at the ma gnetosphere/disk boundary.