Jets from young stars: estimates of their physical parameters

On the basis of existing observational data, the characteristic values of the physical parameters of jets from young stellar objects are estimated. The results of these estimates are as follows: velocities = 200–400 km/s, Mach numbers = 10–40, hydrogen-number densities = 15–150 cm−3, and mass fluxes = 10−10–10−7 [Formula: see text]. The derived Mach numbers imply reasonable jet temperatures (≈ 104 K), being consistent with the observed emission-line spectrum. The estimated jet densities are in agreement with the idea that some high-velocity Herbig–Haro objects (v ≈ 200 km/s) represent the working surface of a freely expanding jet boring through the outer, tenuous parts of a molecular cloud.