arXiv 2212.082612022-12-16astro-ph.SRastro-ph.EP

低增长率人口普查。II：吸积特性

A Census of the Low Accretors. II: Accretion Properties

Thanawuth Thanathibodee, Brandon Molina, Javier Serna, Nuria Calvet, Jesús Hernández, James Muzerolle, Ramiro Franco-Hernández

备注：: Accepted for publication in The Astrophysical Journal
DOI：: 10.3847/1538-4357/acac84

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摘要：

关于驱动吸积从原行星盘到低质量前主序星（金牛T星）的过程，我们已经知道很多。然而，吸积是如何停止的还不清楚。为了确定吸积性质及其与恒星性质的关系，并深入了解吸积的最后阶段，我们提出了一个详细的分析24低和可能的吸积物，以前确定使用He I $λ$ 10830线。我们的模型中分辨率H $α$配置文件的这些恒星使用磁层吸积流模型，占色球的贡献在线中心。基于20颗恒星的拟合参数，我们发现圆盘截断半径和质量吸积率之间的幂律关系与理论和模拟预测一致。通过比较共转半径和截断半径，我们发现大多数目标都处于不稳定的吸积状态，并排除了螺旋桨是阻止吸积的主要过程。对于截断半径是相同的磁半径，偶极磁场和/或效率参数$ξ$需要小于先前确定的，这表明高阶场占主导地位，在低吸积率。最后，我们确定的最低吸积率，可以检测到的H $α$线模拟是$1-3\times10^{-11}M_{\odot}yr^{-1}$的M3星和$3-5\times10^{-11}M_{\odot}yr^{-1}$的K5星。这些极限低于我们样品中观察到的吸积速率，表明我们已经达到了物理下限。这个极限，$\dot{M}\sim10^{-10}M_{\odot}yr^{-1}$，是一致的EUV占主导地位的光蒸发。

英文摘要：

Much is known about the processes driving accretion from protoplanetary disks onto low-mass pre-main-sequence stars (T Tauri stars). Nevertheless, it is unclear how accretion stops. To determine the accretion properties and their relation to stellar properties and gain insight into the last stages of accretion, we present a detailed analysis of 24 low and possible accretors, previously identified using the He I $λ$10830 line. We model moderate-resolution H$α$ profiles of these stars using magnetospheric accretion flow models that account for the chromospheric contribution at the line center. Based on parameters derived from the fits of 20 stars that can be reproduced with the models, we find a power-law relation between the disk truncation radius and the mass accretion rate consistent with predictions from theory and simulations. Comparing the corotation and truncation radii, we find that most of our targets are accreting in the unstable regime and rule out the propeller as the main process stopping accretion. For the truncation radius to be the same as the magnetic radius, the dipole magnetic field and/or the efficiency parameter $ξ$ need to be smaller than previously determined, suggesting that higher-order fields dominate in low accretion rates. Lastly, we determine that the lowest accretion rates that can be detected by H$α$ line modeling are $1-3\times10^{-11}M_{\odot}yr^{-1}$ for M3 stars and $3-5\times10^{-11}M_{\odot}yr^{-1}$ for K5 stars. These limits are lower than the observed accretion rates in our sample, suggesting that we have reached a physical lower limit. This limit, $\dot{M}\sim10^{-10}M_{\odot}yr^{-1}$, is consistent with EUV-dominated photoevaporation.

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