Turbulent Bipolar Outflows in Young Stellar Objects: Multifractal Universality Classes and Generalized Scaling

We present a study of the scaling properties of bipolar outflows, generic to the circumstellar environment of young stellar objects, and which are generally believed to be magnetohydrodynamically driven. Our work consists of a multifractal analysis of near-infrared light scattered by dust grains in the lobes of seven bipolar nebulae, namely GGD 18, V380 Orionis, LkHα 101/NGC 1579, LkHα 233, PV Cephei, V645 Cygni (GL 2789), and V633 Cassiopeiae (LkHα 198). We argue that these objects pertain to a multifractal universality class, with the corresponding universal parameters averaged over the ensemble yielding α = 1.96 ± 0.02, C1 = 0.04 ± 0.02, and H = 0.7 ± 0.2; these results might suggest that the dynamics of the observed objects are similar. We then proceed to investigate the existence of anisotropy in the scaling of GGD 18 using the Generalized Scale Invariance (GSI) formalism. It is found that differential rotation and stratification are involved in the outflow mechanism. The stratification is believed to be dynamical in nature i.e., gravity is apparently not the dominant stratifying force. Current address: Massachusetts Institute of Technology, Physics Department, 77 Massachusetts Avenue, Cambridge, MA 02139, USA; email address: [email protected] email address: [email protected] Guest observer at the Canada-France-Hawaii telescope.