Jets from T Tauri stars - Spectroscopic evidence and collimation mechanism

Abstract

Based upon analysis of observed O I (6300 A) forbidden line profiles, it is argued that two separate gas components contribute to the forbidden line emission from T Tauri stars. There is a high-speed component due to a wind from the star, and a low-speed component due to a wind from the circumstellar disk and/or a warm disk corona. Further, most of the high-speed gas particles have velocity vectors nearly parallel to one another, indicating a well-collimated flow. The collimation of an initially radially expanding wind is ascribed to the effect of the magnetic field produced by currents in the circumstellar disk. Assuming that this magnetic field is roughly parallel to the stellar rotation axis, the stellar wind will be collimated into bipolar jets. It is estimated that the disk radius is about 100 AU, the disk magnetic field is about 0.1 G, and the stellar mass-loss rate is about 10 to the -7th solar masses/yr. The orientation of the disk can be deduced from the velocity displacement of the jet emission from the stellar rest velocity. 11 references.