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arXiv 1902.04081astro-ph.EPastro-ph.SR
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ALMA揭示的$β$风景如画带中类似柯伊伯带的小行星倾斜的热和冷星群

Kuiper Belt-Like Hot and Cold Populations of Planetesimal Inclinations in the $β$ Pictoris Belt Revealed by ALMA

Luca Matrà, Mark C. Wyatt, David J. Wilner, William R. F. Dent, Sebastian Marino, Grant M. Kennedy, Julien Milli

摘要:

柯伊伯带的倾角分布对其起源和动力学演化提供了独特的约束,激发了对太阳系外小行星带的垂直分辨观测。我们目前的ALMA观测毫米波发射在近边缘的星子带周围$β$风景如画,发现垂直分布是更好地描述了两个高斯相比,一个单一的高斯的总和。这表明,对于柯伊伯带,$β$ Pic带的倾角分布更好地描述了动力热和冷人口的总和,而不是一个单一的组成部分。热的和冷的种群具有8.9 $^{+0.7}_{-0.5}$和1.1 $^{+0.5}_{-0.5}$度的RMS倾角。我们还报告说,一个轴对称带模型提供了一个很好的适合新的和档案的ALMA vibrium,并确认中平面是不对齐的$β$图片b的轨道平面。然而,我们没有发现显着的证据,无论是在散射光和CO排放或西南/东北(SW/NE)不对称先前报告毫米发射观察到的内盘倾斜。最后,我们考虑带的倾角分布的起源。长期扰动从$β$图b不太可能提供足够的动力加热来解释整个带的径向范围内的热人口,和粘性搅拌带内的大机构单独不能复制观察到的两个人口。这就提出了一种替代或额外的情况,例如星子出生时具有高倾角,或者存在一颗“$β$ Pic c”行星,可能会在带的内边缘附近向外迁移。

英文摘要:

The inclination distribution of the Kuiper belt provides unique constraints on its origin and dynamical evolution, motivating vertically resolved observations of extrasolar planetesimal belts. We present ALMA observations of millimeter emission in the near edge-on planetesimal belt around $β$ Pictoris, finding that the vertical distribution is significantly better described by the sum of two Gaussians compared to a single Gaussian. This indicates that, as for the Kuiper belt, the inclination distribution of $β$ Pic's belt is better described by the sum of dynamically hot and cold populations rather than a single component. The hot and cold populations have RMS inclinations of 8.9$^{+0.7}_{-0.5}$ and 1.1$^{+0.5}_{-0.5}$ degrees. We also report that an axisymmetric belt model provides a good fit to new and archival ALMA visibilities, and confirm that the midplane is misaligned with respect to $β$ Pic b's orbital plane. However, we find no significant evidence for either the inner disk tilt observed in scattered light and CO emission or the South-West/North-East (SW/NE) asymmetry previously reported for millimeter emission. Finally, we consider the origin of the belt's inclination distribution. Secular perturbations from $β$ Pic b are unlikely to provide sufficient dynamical heating to explain the hot population throughout the belt's radial extent, and viscous stirring from large bodies within the belt alone cannot reproduce the two populations observed. This argues for an alternative or additional scenario, such as planetesimals being born with high inclinations, or the presence of a `$β$ Pic c' planet, potentially migrating outwards near the belt's inner edge.

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