Spectral signatures of disk eccentricity in young binary systems - I. Circumprimary case
Spectral signatures of disk eccentricity in young binary systems - I. Circumprimary case
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年轻双星系统中盘偏心率的光谱特征 - I. 周边情况
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发表时间：
2011
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通讯作者：
László L. Kiss
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作者：
Z. Regály;Z. Sándor;C. Dullemond;László L. Kiss;László L. Kiss
上下文星星的形成是通过分子云的分裂而发生的，这意味着大多数诞生的恒星都是双星系统的成员。越来越多的证据表明，行星可能形成于中等分离度（1050 Au）的双星的环主盘中。由副行星引起的潮汐力通常会使原本圆形的绕主星盘变形为偏心盘。由于盘偏心率可能在行星形成中发挥重要作用，因此了解它如何演变非常重要。目标。我们研究了盘偏心率的演化，揭示了它对双星系统和原行星盘的物理参数的依赖性。为了从高分辨率近红外光谱推断盘的偏心性，我们计算了从偏心盘的大气中出现的CO分子的基本带（4.7 μm）发射线。方法.我们使用二维基于网格的流体动力学代码，假设α-型粘度的轨道次要的引力扰动下的环主盘的演变模型。流体动力学的结果与我们的半解析光谱代码相结合，计算CO分子线的轮廓。我们的热盘模型是基于双层盘模型近似。我们假设LTE和典型的尘埃和气体的性质的circumprimary磁盘。结果我们发现，气体包裹的轨道速度分布显着不同的圆形开普勒时尚。谱线轮廓呈双峰状，形状不对称。非对称性的大小对二元质量比、粘度（α）的大小和盘质量不敏感。相比之下，磁盘偏心率，从而线轮廓不对称的幅度，是显着的二进制偏心率和磁盘的几何厚度的影响。结论.我们表明，磁盘偏心率分布在行星形成区域可以通过拟合高分辨率CO线轮廓不对称使用一个简单的二维光谱模型，占磁盘偏心率所造成的速度失真。因此，与我们的新方法的磁盘偏心率可以推断从高分辨率近红外光谱数据之前获得的高角分辨率光学（ELT）或无线电（阿尔马，E-VLA）直接成像的时代。通过确定中等分离的年轻双星的盘偏心率，我们可能能够限制行星形成理论。
Context. Star formation occurs via fragmentation of molecular clouds, which means that the majority of stars born are members of binary systems. There is growing evidence that planets might form in circumprimary disks of medium-separation (≲50 AU) binaries. The tidal forces caused by the secondary generally act to distort the originally circular circumprimary disk to an eccentric one. Since the disk eccentricity might play a major role in planet formation, it is of great importance to understand how it evolves. Aims. We investigate disk eccentricity evolution to reveal its dependence on the physical parameters of the binary system and the protoplanetary disk. To infer the disk eccentricity from high-resolution near-IR spectroscopy, we calculate the fundamental band (4.7 μm) emission lines of the CO molecule emerging from the atmosphere of the eccentric disk. Methods. We model circumprimary disk evolution under the gravitational perturbation of the orbiting secondary using a 2D grid-based hydrodynamical code, assuming α-type viscosity. The hydrodynamical results are combined with our semianalytical spectral code to calculate the CO molecular line profiles. Our thermal disk model is based on the double-layer disk model approximation. We assume LTE and canonical dust and gas properties for the circumprimary disk. Results. We find that the orbital velocity distribution of the gas parcels differs significantly from the circular Keplerian fashion. The line profiles are double-peaked and asymmetric in shape. The magnitude of asymmetry is insensitive to the binary mass ratio, the magnitude of viscosity (α), and the disk mass. In contrast, the disk eccentricity, thus the magnitude of the line profile asymmetry, is influenced significantly by the binary eccentricity and the disk geometrical thickness. Conclusions. We demonstrate that the disk eccentricity profile in the planet-forming region can be determined by fitting the high-resolution CO line profile asymmetry using a simple 2D spectral model that accounts for the velocity distortions caused by the disk eccentricity. Thus, with our novel approach the disk eccentricity can be inferred from high-resolution near-IR spectroscopy data acquired prior to the era of high angular resolution optical (ELT) or radio (ALMA, E-VLA) direct-imaging. By determining the disk eccentricity in medium-separation young binaries, we might be able to constrain the planet formation theories.