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arXiv 1712.02420astro-ph.SR
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慢脉动B星中热驱动g模的Angular momentum输运

Angular momentum transport by heat-driven g-modes in slowly pulsating B stars

R. H. D. Townsend, J. Goldstein, E. G. Zweibel

摘要:

出于最近的兴趣在大质量恒星中的波传输现象,我们研究是否热驱动的重力(g)模式在缓慢脉动B(SPB)星激发可以显着修改恒星的内部旋转。我们开发了一个形式主义的差分扭矩施加g模式,并实现此形式主义使用的GYRE振荡代码和MESASTAR恒星演化代码。首先集中在一个$4.21$ $M_\odot$模型,我们模拟了1,000年的恒星演化的扭矩的综合影响下,由于一个单一的不稳定的旋转g模式(与振幅的基础上选择的观测约束),和扩散角动量输运由于对流,过冲,和旋转不稳定性。我们发现,g模式迅速提取角动量从表面层,沉积在恒星内部更深。角动量输运是如此有效,以至于在模拟结束时,最初不旋转的表面层以逆行方向旋转到临界速率的$\approx30\%$。然而,在我们的模拟中额外包含磁应力,几乎完全抑制了这种自旋。扩展我们的模拟,以涵盖整个不稳定带,我们发现,在所有的SPB星相同的一般行为。在提供了一些说明以将我们的结果置于背景中之后,我们假设观察到的SPB恒星表面旋转较慢(与其他B型恒星相比)可能是我们模拟证明的角动量传输的直接后果。

英文摘要:

Motivated by recent interest in the phenomenon of waves transport in massive stars, we examine whether the heat-driven gravity (g) modes excited in slowly-pulsating B (SPB) stars can significantly modify the stars' internal rotation. We develop a formalism for the differential torque exerted by g modes, and implement this formalism using the GYRE oscillation code and the MESASTAR stellar evolution code. Focusing first on a $4.21$ $M_\odot$ model, we simulate 1,000 years of stellar evolution under the combined effects of the torque due to a single unstable prograde g mode (with an amplitude chosen on the basis of observational constraints), and diffusive angular momentum transport due to convection, overshooting, and rotational instabilities. We find that the g mode rapidly extracts angular momentum from the surface layers, depositing it deeper in the stellar interior. The angular momentum transport is so efficient that by the end of the simulation the initially non-rotating surface layers are spun in the retrograde direction to $\approx30\%$ of the critical rate. However, the additional inclusion of magnetic stresses in our simulations, almost completely inhibits this spin-up. Expanding our simulations to cover the whole instability strip, we show that the same general behavior is seen in all SPB stars. After providing some caveats to contextualize our results, we hypothesize that the observed slower surface rotation of SPB stars (as compared to other B-type stars) may be the direct consequence of the angular momentum transport that our simulations demonstrate.

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