大质量不平衡转捩盘的气体和尘埃流体动力学模拟- II。粉尘浓度
Gas and dust hydrodynamical simulations of massive lopsided transition discs - II. Dust concentration
摘要：
我们通过二维流体动力学模拟，包括气体和尘埃，研究了大规模不平衡过渡盘中大尘埃颗粒的动力学。我们的模拟采用了环状的气体密度分布，对Rossby波不稳定性变得不稳定，并形成一个大的新月形涡。当气体的自引力被丢弃，但从位移的恒星的旋涡的间接力包括在内，我们确认，尘埃颗粒停止时间的顺序的轨道时间，这应该是典型的几厘米的大小，被困在前方的旋涡在方位角方向，而最小和最大的颗粒集中在旋涡中心。我们获得约25度的最大偏移角。气体的自重作用使大小颗粒之间的浓度差异更加明显。在低到中等的圆盘质量下，颗粒越大，它们被困在旋涡前面的距离就越远。位移角高达90度，达到10厘米大小的颗粒，我们表明，这样大的偏移可以产生一个双峰连续发射在毫米/厘米波长观察。这种现象的发生是因为大颗粒在涡旋重力的作用下相对于涡旋发生马蹄形U形转弯。在大圆盘质量下，由于涡流的图案频率变得越来越慢于开普勒，小颗粒稍微集中在涡流之外，大颗粒在涡流的径向位置周围形成通常非轴对称的环状结构。因此，气体自引力赋予了大小尘埃颗粒不同的捕获位置，这可能会被当前和未来的观测所探测，这表明在旋涡中形成星子可能比以前想象的更困难。
英文摘要：
We investigate the dynamics of large dust grains in massive lopsided transition discs via 2D hydrodynamical simulations including both gas and dust. Our simulations adopt a ring-like gas density profile that becomes unstable against the Rossby-wave instability and forms a large crescent-shaped vortex. When gas self-gravity is discarded, but the indirect force from the displacement of the star by the vortex is included, we confirm that dust grains with stopping times of order the orbital time, which should be typically a few centimetres in size, are trapped ahead of the vortex in the azimuthal direction, while the smallest and largest grains concentrate towards the vortex centre. We obtain maximum shift angles of about 25 degrees. Gas self-gravity accentuates the concentration differences between small and large grains. At low to moderate disc masses, the larger the grains, the farther they are trapped ahead of the vortex. Shift angles up to 90 degrees are reached for 10 cm-sized grains, and we show that such large offsets can produce a double-peaked continuum emission observable at mm/cm wavelengths. This behaviour comes about because the large grains undergo horseshoe U-turns relative to the vortex due to the vortex's gravity. At large disc masses, since the vortex's pattern frequency becomes increasingly slower than Keplerian, small grains concentrate slightly beyond the vortex and large grains form generally non-axisymmetric ring-like structures around the vortex's radial location. Gas self-gravity therefore imparts distinct trapping locations for small and large dust grains which may be probed by current and future observations, and which suggest that the formation of planetesimals in vortices might be more difficult than previously thought.
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