FREE-FREE RADIO EMISSION FROM YOUNG STELLAR OBJECTS

We calculate the centimeter wavelength free-free emission of the jets of young stellar objects (YSOs) with the X-wind model enhanced by a variety of physical processes. Using parameters characteristic of a Class I YSO with a mass-loss rate of ∼10^-6 M_⊙ yr^-1, we obtain a 3.6 cm map and a spectral index that compare well with high spatial resolution observations of L1551 1RS 5. Models with lower mass-loss rates, appropriate for Class II YSOs with revealed optical jets, produce radio jets that are too weak to be detected at current sensitivity levels. In addition to demonstrating the consistency of the density distribution of the X-wind model with observations, we are able to obtain information on the processes that heat and ionize the inner jet, i.e., X-ray ionization and shock heating and ionization.