局部等温径向结构自引力盘中的单臂螺旋
One-armed spirals in locally isothermal, radially structured self-gravitating discs
摘要：
我们描述了一种新的机制，导致不稳定的非轴对称波在天体物理光盘施加径向温度梯度。例如，这可能适用于原行星盘的外部。我们使用线性密度波理论表明，非轴对称扰动一般不保存其角动量在强迫温度梯度的存在下。这意味着线性扰动和背景盘之间的角动量交换。特别是，当扰动是一个低频的拖尾波和磁盘温度向外下降，这种相互作用是不稳定的，并导致波的增长。我们证明了这种现象，通过局部等温盘在2D中使用FARGO代码和在3D中与ZEUS-MP和PLUTO代码的数值流体动力学模拟。我们考虑径向结构的光盘与自引力区域保持稳定的温度梯度的情况下。然而，当施加温度梯度时，我们观察到单臂螺旋模式（方位波数$m=1$）的指数增长，其中在旋臂的大部分之外具有共旋半径，从而导致接近静止的单臂螺旋图案。这种单臂螺旋的发展并不需要中心恒星的运动，正如以前的研究所发现的那样。由于强迫温度梯度的不稳定并不明确需要光盘自重，我们认为这种机制也可能会影响低频单臂振荡非自引力光盘。
英文摘要：
We describe a new mechanism that leads to the destabilisation of non-axisymmetric waves in astrophysical discs with an imposed radial temperature gradient. This might apply, for example, to the outer parts of protoplanetary discs. We use linear density wave theory to show that non-axisymmetric perturbations generally do not conserve their angular momentum in the presence of a forced temperature gradient. This implies an exchange of angular momentum between linear perturbations and the background disc. In particular, when the disturbance is a low-frequency trailing wave and the disc temperature decreases outwards, this interaction is unstable and leads to the growth of the wave. We demonstrate this phenomenon through numerical hydrodynamic simulations of locally isothermal discs in 2D using the FARGO code and in 3D with the ZEUS-MP and PLUTO codes. We consider radially structured discs with a self-gravitating region which remains stable in the absence of a temperature gradient. However, when a temperature gradient is imposed we observe exponential growth of a one-armed spiral mode (azimuthal wavenumber $m=1$) with co-rotation radius outside the bulk of the spiral arm, resulting in a nearly-stationary one-armed spiral pattern. The development of this one-armed spiral does not require the movement of the central star, as found in previous studies. Because destabilisation by a forced temperature gradient does not explicitly require disc self-gravity, we suggest this mechanism may also affect low-frequency one-armed oscillations in non-self-gravitating discs.
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