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arXiv 1209.6410astro-ph.SR
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前主序星通过日冕物质抛射的质量损失和angular momentum损失的意义

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

Alicia Aarnio, Sean Matt, Keivan Stassun

摘要:

我们发展了一个经验模型来估算太阳型前主序星(PMS)通过日冕物质抛射(CME)的质量损失率。我们的方法从观测到的PMS X射线耀斑能量估计CME质量损失率,使用我们经验确定的太阳X射线耀斑能量和CME质量之间的关系:log(M_CME [g])= 0.63 x log(E_flare [erg])- 2.57。使用质量确定的最大耀斑的磁性结构上观察到的PMS星,我们建议,这种太阳校准的关系可能会保持超过10个数量级的耀斑能量和7个数量级的CME质量。我们计算的典型太阳型PMS星的CME总质量损失率在1 e-12到1 e-9 Msun/yr之间。然后,我们使用这些CME质量损失率的估计,以推断随之而来的角动量损失导致的主要序列。假设一颗典型的~1 M_sun T Tauri星的CME流出速率<1 e-10 M_sun/yr,那么在最初的~ 100万年期间,由此产生的自旋下降力矩太小,不足以抵消由于收缩和吸积而引起的恒星自旋上升。然而,如果CME的质量损失率大于1 e-10 M_sun/yr,在我们的计算允许的范围内,CME的自旋下降力矩可能会影响到几百万年后恒星的自旋演化。

英文摘要:

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.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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