Name/Affiliation: Claire Davies (The University of St Andrews)
Accretion discs as regulators of stellar angular momentum evolution in the ONC and Taurus
Stars form from the collapse of dense molecular cloud cores. If angular momentum was conserved during their contraction, stars would reach rotational velocities in excess of those required to break them apart. However, stars with accretion discs are found to be rotating well below break-up speed, suggesting that an angular momentum removal mechanism must operate - likely some form of outflow. Previous observational studies of stellar angular momentum evolution have primarily focused on the apparent relationship between stellar rotation periods and indicators of disc presence or accretion. Here, we calculate the stellar angular momentum and compare its evolution in stars with and without accretion discs. Our study focusses on two of the youngest, nearby regions of star formation, namely the Orion Nebula Cluster and Taurus. The stellar masses, radii, and ages are recalculated in a consistent manner, using recently published intrinsic colours for pre-main sequence stars and their most up-to-date spectral types. We ensure the reliability of the stellar rotation periods by carefully removing all previously reported sources of bias. This results in a consistent sample of fully convective stars of spectral type K0 to M6.5 in these two regions. Our findings reinforce previous results suggesting the importance of accretion discs in regulating the early evolution of stellar angular momentum. Furthermore, we show that the efficiency of this process is related to the lifetime of the disc.