A Transition of Dynamo Modes in M Dwarfs: Narrowing Down the Spectral Range Where the Transition Occurs
A Transition of Dynamo Modes in M Dwarfs: Narrowing Down the Spectral Range Where the Transition Occurs
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M矮星中发电机模式的转变：缩小转变发生的光谱范围
DOI：
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发表时间：
2020
影响因子：
4.9
通讯作者：
É. Houdebine
中科院分区：
文献类型：
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作者：
D. Mullan;É. Houdebine
Houdeine等人。结合CaⅡ数据和投影旋转速度(V Sin I)，建立了K-M矮星的自转-活动关联(RAC)。RAC斜率被用来论证发电机模式之间的转换发生在M2和M3之间的频谱类型。H17提出发电机的转变对应于完全对流转变(TTCC)。一项对盖亚数据的独立研究导致了Jao等人。建议TTCC设置在“M3.0V附近”，接近H17的结果。然而，在GAIA数据中引起TTCC特征的恒星变化可能不会导致相同光谱类型的CaII发射的变化：后者也受到磁效应的影响，这取决于核心对流的某些性质。在这里，我们使用∼600M矮星样本中的钙II发射通量，并试图缩小从一种发电机模式到另一种发电机模式的转变范围：我们不依赖于RAC斜率，而是量化钙II发射通量如何随光谱类型而变化，以确定在狭窄的光谱类型范围内通量显著下降的“阶跃”。我们建议，发电机模式的转变可以缩小到M2.1和M2.3之间。这接近于Jao等人确定的TTCC地点，但早于该地点。我们认为，发电机模式的转变可能与小对流核的存在有关，在某些低质量恒星中，小对流核在有限的时间间隔内发生。
Houdebine et al. combined Ca ii data with projected rotational velocities (v sin i) to construct rotation-activity correlations (RAC) in K-M dwarfs. The RAC slopes were used to argue that a transition between dynamo modes occurs at a spectral type between M2 and M3. H17 suggested that the dynamo transition corresponds to a transition to complete convection (TTCC). An independent study of GAIA data led Jao et al. to suggest that the TTCC sets in “near M3.0V,” close to the H17 result. However, the changes in a star that cause TTCC signatures in GAIA data might not lead to changes in Ca ii emission at an identical spectral type: the latter are also affected by magnetic effects, which depend on certain properties of convection in the core. Here, we use Ca ii emission fluxes in a sample of ∼600 M dwarfs, and attempt to narrow down the transition from one dynamo mode to another: rather than relying on RAC slopes, we quantify how the Ca ii emission flux varies with spectral type to identify “steps” where the flux decreases significantly across a narrow range of spectral types. We suggest that the dynamo mode transition may be narrowed down to between M2.1 and M2.3. This is close to, but earlier than, the TTCC location identified by Jao et al. We suggest that the transition in dynamo mode may be related to the existence of a small convective core, which occurs for a finite time interval in certain low-mass stars.
影响因子：
7.9
作者：
Jao, Wei-Chun;Henry, Todd J.;Hambly, Nigel C.
通讯作者：
Hambly, Nigel C.