He I λ10830 as a Probe of Winds in Accreting Young Stars

He I λ10830 profiles acquired with Keck’s NIRSPEC for 6 young low mass stars with high disk accretion rates (AS 353A, DG Tau, DL Tau, DR Tau, HL Tau and SVS 13) provide new insight into accretion-driven winds. In 4 stars the profiles have the signature of resonance scattering, and possess a deep and broad blueshifted absorption that penetrates more than 50% into the 1 μm continuum over a continuous range of velocities from near the stellar rest velocity to the terminal velocity of the wind, unlike inner wind signatures seen in other spectral features. This deep and broad absorption provides the first observational tracer of the acceleration region of the inner wind and suggests that this acceleration region is situated such that it occults a significant portion of the stellar disk. The remaining 2 stars also have blue absorption extending below the continuum although here the profiles are dominated by emission, requiring an additional source of helium excitation beyond resonant scattering. This is likely the same process that produces the emission profiles seen at He I λ5876. Subject headings: stars: formation, winds, outflows, protoplanetary disks, pre– main-sequence Guest Observer, Gemini/Keck-NIRSPEC program Visiting Astronomer, Keck Observatory Five College Astronomy, Smith College, Northampton, MA 10163, [email protected] Five College Astronomy, University of Massachusetts, Amherst, MA, 01003 [email protected], [email protected] Dept. of Astronomy, California Institute of Technology, Pasadena, CA 91125, [email protected] Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 01238, [email protected]