  Strong stellar magnetic fields are believed to truncate the inner accretion
disks around young stars, redirecting the accreting material to the high
latitude regions of the stellar surface. In the past few years, observations of
strong stellar fields on T Tauri stars with field strengths in general
agreement with the predictions of magnetospheric accretion theory have
bolstered this picture. Currently, nothing is known about the magnetic field
properties of younger, more embedded Class I young stellar objects (YSOs). It
is believed that protostars accrete much of their final mass during the Class I
phase, but the physics governing this process remains poorly understood. Here,
we use high resolution near infrared spectra obtained with NIRSPEC on Keck and
with Phoenix on Gemini South to measure the magnetic field properties of the
Class I protostar WL 17. We find clear signatures of a strong stellar magnetic
field. Analysis of this data suggests a surface average field strength of $2.9
\pm 0.43$ kG on WL 17. We present our field measurements and discuss how they
fit with the general model of magnetospheric accretion in young stars.

Solar and Stellar Astrophysics