Mass Loss in Pre-Main-Sequence Stars via Coronal Mass Ejections and Implications for Angular Momentum Loss

We develop an empirical model to estimate mass-loss rates via coronal mass ejections (CMEs) for solar-type pre-main-sequence (PMS) stars. Our method estimates the CME mass-loss rate from the observed energies of PMS X-ray flares, using our empirically determined relationship between solar X-ray flare energy and CME mass: log ( M CME [g]) = 0.63 × log ( E flare [erg]) − 2.57. Using masses determined for the largest flaring magnetic structures observed on PMS stars, we suggest that this solar-calibrated relationship may hold over 10 orders of magnitude in flare energy and 7 orders of magnitude in CME mass. The total CME mass-loss rate we calculate for typical solar-type PMS stars is in the range 10 −12 –10 −9 M ☉ yr −1 . We then use these CME mass-loss rate estimates to infer the attendant angular momentum loss leading up to the main sequence. Assuming that the CME outflow rate for a typical ∼1 M ☉ T Tauri star is <10 −10 M ☉ yr −1 , the resulting spin-down torque is too small during the first ∼1 Myr to counteract the stellar spin-up due to contraction and accretion. However, if the CME mass-loss rate is ≳ 10 −10 M ☉ yr −1 , as permitted by our calculations, then the CME spin-down torque may influence the stellar spin evolution after an age of a few Myr.