从实验室缩比实验推断EXOR型天体吸积流入的可能磁场强度
Inferring possible magnetic field strength of accreting inflows in EXor-type objects from scaled laboratory experiments
摘要：
目的。EXor类天体是原恒星，它们显示出由间歇性和强烈的磁层吸积事件引起的强烈紫外光爆发。这些物体还没有得到很好的研究，很难确定其特征。几个参数，如等离子体流的速度，特征密度和温度，可以从目前的观测检索。然而，到目前为止，还没有关于磁场值的信息，确切的吸积情况也在讨论中。方法.我们使用实验室等离子体，由高功率激光器撞击固体靶或由等离子体枪注入器产生，并使这些等离子体垂直于强外部磁场传播。传播的等离子体被发现是很好地缩放到目前推断的EXOR型吸积事件的参数，从而使我们能够研究这种情节吸积过程中的行为缩放条件。结果我们提出了一个额外的物质吸积在赤道平面的情况下，声称解释的EXor对象的吸积率增加，通过实验证明，有效的等离子体传播整个磁场的支持。特别是，我们的实验室调查使我们能够确定，在吸积流的EXOR对象，在截断半径和恒星表面之间的中间位置的场强，应该是100高斯的顺序。反过来，这表明恒星表面的场强为几千高斯，这与从经典金牛座T星的观测中推断出的值相似。
英文摘要：
Aims. EXor-type objects are protostars that display powerful UV-optical outbursts caused by intermittent and powerful events of magnetospheric accretion. These objects are not yet well investigated and are quite difficult to characterize. Several parameters, such as plasma stream velocities, characteristic densities, and temperatures, can be retrieved from present observations. As of yet, however, there is no information about the magnetic field values and the exact underlying accretion scenario is also under discussion. Methods. We use laboratory plasmas, created by a high power laser impacting a solid target or by a plasma gun injector, and make these plasmas propagate perpendicularly to a strong external magnetic field. The propagating plasmas are found to be well scaled to the presently inferred parameters of EXor-type accretion event, thus allowing us to study the behaviour of such episodic accretion processes in scaled conditions. Results. We propose a scenario of additional matter accretion in the equatorial plane, which claims to explain the increased accretion rates of the EXor objects, supported by the experimental demonstration of effective plasma propagation across the magnetic field. In particular, our laboratory investigation allows us to determine that the field strength in the accretion stream of EXor objects, in a position intermediate between the truncation radius and the stellar surface, should be of the order of 100 gauss. This, in turn, suggests a field strength of a few kilogausses on the stellar surface, which is similar to values inferred from observations of classical T Tauri stars.
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