Program: GS-2006A-C-12

We propose to measure the magnetic fields of several slowly rotating embedded Class I and flat spectrum protostars by observing their magnetically sensitive 2.2239 um Ti I line with Phoenix. We shall use these measurements to determine whether these objects are accumulating mass in a manner consistent with modern magnetospheric accretion models. This will be done by applying the magnetospheric accretion equations to the stellar parameters which we have recently published for these objects, and we will evaluate whether the magnetic truncation radii of their circumstellar disks correspond to their stellar co-rotation radii as predicted by the models. Our previous analysis of the protostar YLW 15 implies that object may be accumulating mass as predicted by the Shu et al. magnetospheric theory if it has a magnetic field of about 1 kG, so we are encouraged that these models may apply to protostars. We now wish to measure the actual fields of these objects to evaluate this in detail. These will be the first measurements of the magnetic fields of embedded protostars, so they will be intrinsically valuable regardless of what they reveal about the accretion properties of these objects.