NEUTRAL INTERSTELLAR HELIUM PARAMETERS BASED ON IBEX-Lo OBSERVATIONS AND TEST PARTICLE CALCULATIONS
NEUTRAL INTERSTELLAR HELIUM PARAMETERS BASED ON IBEX-Lo OBSERVATIONS AND TEST PARTICLE CALCULATIONS
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DOI：
10.1088/0067-0049/198/2/12
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发表时间：
2012-02-01
影响因子：
8.7
通讯作者：
McComas, D. J.
中科院分区：
文献类型：
--
作者：
Bzowski, M.;Kubiak, M. A.;McComas, D. J.
中性星际氦（NISHe）由于其高电离势和与氢的弱相互作用，在与星际介质的日光层界面几乎不受影响，并自由进入太阳系。这个第二丰富的物种提供了一些关于本地星际云中星际气体特征的最佳信息。星际边界探测器（IBEX）是第二个直接探测NISHe的使命。我们提出了一个比较最近的IBEX NISHe观测和模拟进行了测试良好的定量模拟代码。模拟和观测结果比较好的时候，测量通量占主导地位的NISHe（和其他物种的贡献很小）。模拟和观测之间的差异表明，以前未被发现的中性氦的第二人口，可能是由星际氦与外日鞘中的等离子体相互作用产生的。星际中性参数在统计学上与以前的主要从GAS/ESTO实验中获得的原位结果不同，但它们确实与从星际吸收研究中获得的局部星际流矢量一致：新建立的流向为黄经79度2，纬-5度1，速度近似为22.8km/s（-1），温度为6200 K。这些新的结果意味着气体的绝对速度显着降低，从而显着降低的动态压力的边界上的日光层和不同的取向的氢偏转平面相比，以前的结果从太阳能电池板。这个平面的不同方向也表明了星际磁场的新几何形状，较低的动态压力需要压力平衡的其他组成部分的补偿，最有可能是更高密度的星际等离子体和星际磁场的强度。
Because of its high ionization potential and weak interaction with hydrogen, neutral interstellar helium (NISHe) is almost unaffected at the heliospheric interface with the interstellar medium and freely enters the solar system. This second most abundant species provides some of the best information on the characteristics of the interstellar gas in the local interstellar cloud. The Interstellar Boundary Explorer (IBEX) is the second mission to directly detect NISHe. We present a comparison between recent IBEX NISHe observations and simulations carried out using a well-tested quantitative simulation code. Simulation and observation results compare well for times when measured fluxes are dominated by NISHe (and contributions from other species are small). Differences between simulations and observations indicate a previously undetected secondary population of neutral helium, likely produced by interaction of interstellar helium with plasma in the outer heliosheath. Interstellar neutral parameters are statistically different from previous in situ results obtained mostly from the GAS/Ulysses experiment, but they do agree with the local interstellar flow vector obtained from studies of interstellar absorption: the newly established flow direction is ecliptic longitude 79 degrees.2, latitude -5 degrees.1, the velocity is similar to 22.8 km s(-1), and the temperature is 6200 K. These new results imply a markedly lower absolute velocity of the gas and thus significantly lower dynamic pressure on the boundaries of the heliosphere and different orientation of the Hydrogen Deflection Plane compared to prior results from Ulysses. A different orientation of this plane also suggests a new geometry of the interstellar magnetic field, and the lower dynamic pressure calls for a compensation by other components of the pressure balance, most likely a higher density of interstellar plasma and strength of interstellar magnetic field.