THE CORONAL ABUNDANCE ANOMALIES OF M DWARFS
THE CORONAL ABUNDANCE ANOMALIES OF M DWARFS
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M矮星的日冕丰度异常
DOI：
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发表时间：
2012
期刊：
影响因子：
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通讯作者：
M. Karovska
中科院分区：
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作者：
Brian E. Wood;J. Laming;M. Karovska
我们分析了M0V+M0V双星GJ338的钱德拉X射线谱。根据X射线表面通量的量化，这些是用X射线光栅光谱学观测到的最不活跃的M矮星。我们的重点是测量日冕丰度，特别是寻找与第一电离势(FIP)有关的丰度异常的证据。在日冕和风中，低FIP元素过剩，这就是所谓的FIP效应。对于其他恒星，特别是非常活跃的恒星，通常会观察到“逆FIP效应”，低FIP元素不足。对于GJ 338双星的两个成员，我们发现了适度的逆FIP效应的证据，这与之前报道的光谱类型和FIP偏差之间的关联的预期一致。这相当于有力的证据表明，所有的M矮星都应该表现出逆FIP效应现象，而不仅仅是活跃的矮星。我们迈出了模拟M矮星逆FIP现象的第一步，建立在过去工作的基础上，这项工作已经证明，MHD波通过冕环可以导致有质动力，以与FIP效应一致的方式分离元素。我们证明，在某些情况下，这个模型也可以导致逆FIP效应，为将来对M矮星日冕丰度进行更详细的模拟指明了方向。
We analyze Chandra X-ray spectra of the M0 V+M0 V binary GJ 338. As quantified by X-ray surface flux, these are the most inactive M dwarfs ever observed with X-ray grating spectroscopy. We focus on measuring coronal abundances, in particular searching for evidence of abundance anomalies related to first ionization potential (FIP). In the solar corona and wind, low-FIP elements are overabundant, which is the so-called FIP effect. For other stars, particularly very active ones, an “inverse FIP effect” is often observed, with low-FIP elements being underabundant. For both members of the GJ 338 binary, we find evidence for a modest inverse FIP effect, consistent with expectations from a previously reported correlation between spectral type and FIP bias. This amounts to strong evidence that all M dwarfs should exhibit the inverse FIP effect phenomenon, not just the active ones. We take the first step toward modeling the inverse FIP phenomenon in M dwarfs, building on past work that has demonstrated that MHD waves coursing through coronal loops can lead to a ponderomotive force that fractionates elements in a manner consistent with the FIP effect. We demonstrate that in certain circumstances this model can also lead to an inverse FIP effect, pointing the way to more detailed modeling of M dwarf coronal abundances in the future.