标题： 太阳风的弱碰撞加速机制 显示英文标题

标题： Acceleration of weakly collisional solar-type winds

摘要： 太阳风的一个基本特性——快速风的高速度——仍未得到令人满意的解释。这主要是由于弱碰撞等离子体的理论处理困难所致。 流体方法隐含地假设介质受到碰撞主导，并且粒子速度分布接近麦克斯韦分布。然而，观测到的太阳风中的电子速度分布显著偏离麦克斯韦分布。 近年来，使用具有超热尾部的速度分布的动能无碰撞模型（称为外球层模型）已经能够再现快速太阳风的高速度。 在这封信中，我们通过将这些模型推广到广泛的日冕条件下，提出了这些模型的新发展。我们还展示了包括碰撞在内的数值模拟获得的新结果。两种方法在没有任何关于能量传输假设的情况下，自洽地计算了热流。 我们表明，这两种方法——外球层模型和碰撞模型——都以问题的基本参数表现出类似的风速变化；如果日冕电子分布具有超热尾部，则两者都会产生快速风速。这表明外球层模型包含了驱动跨音速恒星风（包括快速太阳风）所需的必要成分。 显示英文摘要

摘要： One of the basic properties of the solar wind, that is the high speed of the fast wind, is still not satisfactorily explained. This is mainly due to the theoretical difficulty of treating weakly collisional plasmas. The fluid approach implies that the medium is collision dominated and that the particle velocity distributions are close to Maxwellians. However the electron velocity distributions observed in the solar wind depart significantly from Maxwellians. Recent kinetic collisionless models (called exospheric) using velocity distributions with a suprathermal tail have been able to reproduce the high speeds of the fast solar wind. In this letter we present new developments of these models by generalizing them over a large range of corona conditions. We also present new results obtained by numerical simulations that include collisions. Both approaches calculate the heat flux self-consistently without any assumption on the energy transport. We show that both approaches - the exospheric and the collisional one - yield a similar variation of the wind speed with the basic parameters of the problem; both produce a fast wind speed if the coronal electron distribution has a suprathermal tail. This suggests that exospheric models contain the necessary ingredients for the powering of a transonic stellar wind, including the fast solar one.