RG Lunch Talk
9 May 2008

Will Fischer 
(UMass, Amherst)

Red Absorption at Helium 10830 as a Probe of CTTS Accretion

High-resolution profiles of He I 10830 are yielding an improved
understanding of the innermost 0.1 AU of T Tauri systems, where gas
accretes from the disk to the star and spectacular outflows are
launched.  The helium profiles of 21/38 CTTS observed with NIRSPEC on
Keck II feature redshifted absorption of the one-micron continuum,
which can be used to probe the geometry of magnetospheric accretion.
I model the red absorption via scattering of the stellar and accretion
shock continua, finding that about half of the red absorptions and
accompanying one-micron veilings are consistent with dipole flows of
moderate width and accretion shock filling factors matching the size
of the magnetospheric footpoints.  The remaining half of the stars
have broad, deep red absorption and low veiling, which require very
wide flows with magnetic footpoints covering 10 to 20% of the stellar
surface but accretion shock filling factors of only 1%.  I model these
profiles with large magnetospheres that are dilutely filled with
accreting gas, leaving the disk over a range of radii in many narrow
"streamlets" but filling only a small fraction of the entire infall
region.  In some cases, accreting streamlets need to extend from
several stellar radii to at least the corotation radius, and in a few
stars, the absorption is so deep at high velocities that non-dipolar
flow geometries need to be considered.