The physics of the MHD disk-jet transition in binary systems: jetted spiral walls launched from disk spiral arms

Abstract

We present a detailed physical analysis of the jet launching mechanism of a circum-stellar disk that is located in a binary system. Applying 3D resistive MHD simulations, we investigate the local and global properties of the system, such as the angular momentum transport and the accretion and ejection mass fluxes. In comparison to previous works, for the first time, we have considered the full magnetic torque, the presence of an outflow, thus the angular momentum transport by vertical motion, and the binary torque. We discuss its specific 3D structure, and how it is affected by tidal effects. We find that the spiral structure evolving in the disk is {\em launched into the outflow}. We propose to call this newly discovered structure a {\em jet spiral wall}. These spiral features follow the same time evolution, with the jet spiral somewhat lagging the disk spiral. We find that the vertical transport of angular momentum has a significant role in the total angular momentum budget also in a binary system. The same holds for the magnetic torque, however, the contribution from the $\phi$-derivative of magnetic pressure and the $B_{\phi}B_r$ stresses are small. The gravity torque arising from the time-dependent 3D Roche potential becomes essential, as it constitutes the fundamental cause for all 3D effects appearing in our disk-jet system. Quantitatively, we find that the disk accretion rate in a binary system increases by $20\%$ compared to a disk around a single star. The disk wind mass flux increases by even 50\%.