揭示最新磁盘的物理状况：L1527中的热嵌入式磁盘
Unveiling the physical conditions of the youngest disks: A warm embedded disk in L1527
摘要：
[摘要]原行星盘已经被广泛研究，包括物理和化学，以了解行星形成的环境。然而，行星形成的第一步可能已经发生，当原恒星和盘仍然嵌入在它们的出生信封。因此，行星形成的初始条件可能是由这些年轻的嵌入盘提供的，其物理和化学结构的特征很差。我们的目标是约束中平面温度结构，一个关键的未知数，嵌入式磁盘周围L1527。特别是，我们着手确定是否有一个扩展的冷的外部区域，CO被冻结，是第二类磁盘的情况下。我们使用档案ALMA数据直接观察近边缘的L1527磁盘的中平面。光学厚$^{13}$ CO（$J=2-1$）和C $^{18}$ O（$J=2-1$）的发射被观察到整个磁盘和内信封，而N $_2$ D $^+ (J=3-2$），这只能是丰富的CO冻结时，没有检测到。两种CO同位素都具有沿中平面的亮度温度$\gtrsim$ 25 K。圆盘和包络发射可以从运动学上分离，因为在圆盘中达到最大速度。在这些速度下使用最高中平面温度构造的幂律径向温度分布表明，温度高于20 K，至少为75 AU，并且可能遍及整个125 AU盘。辐射转移模型表明，一个模型没有CO冻结出的磁盘匹配的C $^{18}$ O观测比一个模型与CO雪线在$\sim$ 70 AU。此外，没有证据表明一个大的（数量级）耗尽的CO。L1527周围的磁盘可能是温暖的，足以有CO存在于整个磁盘的气相，这表明年轻的嵌入磁盘确实可以比更先进的II类磁盘温暖。
英文摘要：
[Abridged] Protoplanetary disks have been studied extensively, both physically and chemically, to understand the environment in which planets form. However, the first steps of planet formation are likely to occur already when the protostar and disk are still embedded in their natal envelope. The initial conditions for planet formation may thus be provided by these young embedded disks, of which the physical and chemical structure is poorly characterized. We aim to constrain the midplane temperature structure, one of the critical unknowns, of the embedded disk around L1527. In particular, we set out to determine whether there is an extended cold outer region where CO is frozen out, as is the case for Class II disks. We use archival ALMA data to directly observe the midplane of the near edge-on L1527 disk. Optically thick $^{13}$CO ($J=2-1$) and C$^{18}$O ($J=2-1$) emission is observed throughout the disk and inner envelope, while N$_2$D$^+ (J=3-2$), which can only be abundant when CO is frozen out, is not detected. Both CO isotopologues have brightness temperatures $\gtrsim$ 25 K along the midplane. Disk and envelope emission can be disentangled kinematically, because the largest velocities are reached in the disk. A power law radial temperature profile constructed using the highest midplane temperature at these velocities suggest that the temperature is above 20 K out to at least 75 AU, and possibly throughout the entire 125 AU disk. Radiative transfer models show that a model without CO freeze-out in the disk matches the C$^{18}$O observations better than a model with the CO snowline at $\sim$70 AU. In addition, there is no evidence for a large (order of magnitude) depletion of CO. The disk around L1527 is likely to be warm enough to have CO present in the gas phase throughout the disk, suggesting that young embedded disks can indeed be warmer than the more evolved Class II disks.
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