The Role of Magnetic Fields in the Pre-Main Sequence Evolution of Solar Type Stars

Abstract

T Tauri stars, being pre-main sequence and solar mass, tell us what our Sun was like when it was very young. T Tauri stars and their protoplanetary disks are ideal astrophysical laboratories for studying the solar system when planets were forming. At the same time, there is no astrophysical laboratory like the present-day Sun for studying in detail the microphysics needed to understand processes involved in early stellar evolution. Specifically, a goal of this work is to understand the role of large-scale structures in stellar magnetic fields. We begin with a general overview of star formation and stellar evolution, focusing on the role of magnetic fields in these processes. Under the broad aegis of star formation and evolution, the remainder of this work aims to methodically explore methods of identifying groups of young stars, star-disk interaction, and a new solar-calibrated pre-main sequence angular momentum loss model. In summary, we begin with a broad focus on a group of young stars, then examine more closely the interaction of young stars with their disks via the stellar magnetic field, and finally we assess other ways in which the field can affect stellar evolution. In searching for a coeval group of young stars, we find the quite surprising result that the particular young trio of stars in question apparently formed separately from any known association or star forming region in the vicinity. Turning then to a well-studied group of million year old stars, the Orion Nebula Cluster, we seek to determine whether a group of young stars' magnetospheres are linked to circumstellar disks. In the majority of cases, we found that large-scale loops do not intersect disk material. This leads naturally into the question of how such large structures then could affect stellar evolution if not via star-disk interaction. We invoke solar physics to relate solar flare flux to corresponding CME mass in order to begin calibration of a stellar CME mass loss rate, the first effort in this field to-date.