Mass loss in pre-main-sequence stars via coronal mass ejections and implications for angular momentum loss.
AARNIO A.N., MATT S.P. and STASSUN K.G.
Abstract (from CDS):
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 (MCME[g]) = 0.63xlog (Eflare[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. 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, 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, as permitted by our calculations, then the CME spin-down torque may influence the stellar spin evolution after an age of a few Myr.