Angular momentum evolution of low‐mass pre‐main sequence stars via extreme coronal mass ejections

Abstract

AbstractThe angular momentum evolution of cool stars during the pre‐main sequence phase of stellar evolution remains a major outstanding problem. Multiple processes are likely involved in the transfer of mass and angular momentum within and out of the star+disk system. The role of coronal mass ejections (CMEs), energetic events which shed mass and magnetic flux in the Sun, has yet to be fully explored in the context of pre‐main sequence stars. It is well established that young, solar‐type stars exhibit X‐ray activity levels up to four orders of magnitude higher than the present‐day Sun, suggesting that CMEs associated with these extreme X‐ray flares could be an important process for expelling mass and angular momentum. We present a novel approach to modeling the CMEs of low‐mass pre‐main sequence stars that uses a solar‐calibrated CME model and observed X‐ray flare rates for young stars. We derive mass loss rates via stellar CMEs and calculate their attendant angular momentum losses during the pre‐main sequence phase. While we find the mass loss rates to be modest, ∼10 % of steady‐state stellar wind values from the literature, the angular momentum losses can be substantial, potentially counteracting the effects of initial stellar spin‐up due to contraction in tens of Myr. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)