Mass loss in pre-main sequence stars via coronal mass ejections and implications for angular momentum loss

TL;DR

This study develops an empirical model linking X-ray flare energies to CME mass-loss rates in pre-main-sequence stars, estimating their impact on stellar angular momentum loss and spin evolution.

Contribution

It introduces a solar-calibrated relationship between flare energy and CME mass that extends over many orders of magnitude, applied to PMS stars for the first time.

Findings

CME mass-loss rates for PMS stars range from 1e-12 to 1e-9 M_sun/yr.

CME-driven angular momentum loss is insufficient to counteract spin-up in the first million years.

CME mass-loss rates above 1e-10 M_sun/yr can influence stellar spin evolution after a few million years.

Abstract

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 x 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 1e-12 to 1e-9 M_sun/yr. We then use these CME mass-loss rate estimates to infer the attendant angular momentum loss leading up to the main sequence. Assuming the CME outflow rate for a typical ~1 M_sun T Tauri star is < 1e-10 M_sun/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 >1e-10 M_sun/yr, as permitted by our calculations, the CME spin-down torque may influence the stellar spin evolution after an age of a few Myr.