JWST imaging of edge-on protoplanetary disks II. Appearance of edge-on disks with a tilted inner region: case study of IRAS04302+2247

We present JWST imaging from 2μm to 21μm of the edge-on protoplanetary disk around the embedded young star IRAS04302+2247. The structure of the source shows two reflection nebulae separated by a dark lane. The source extent is dominated by the extended filamentary envelope at ∼4.4μm and shorter wavelengths, transitioning at 7μm and longer wavelengths to more compact lobes of scattered light from the disk itself. The dark lane thickness does not vary significantly with wavelength, which we interpret as an indication for intermediate-sized (∼ 10μm) grains in the upper layers of the disk. Intriguingly, we find that the brightest nebula of IRAS40302 switches side between 12.8 μm and 21 μm. We explore the effect of a tilted inner region on the general appearance of edge-on disks. We find that radiative transfer models of a disk including a tilted inner region can reproduce an inversion in the brightest nebula. In addition, for specific orientations, the model also predicts strong lateral asymmetries, which can occur for more than half possible viewing azimuths. A large number of edge-on protoplanetary disks observed in scattered light show such lateral asymmetries (15/20), which suggests that a large fraction of protoplanetary disks might host a tilted inner region. Stellar spots may also induce lateral asymmetries, which are expected to vary over a significantly shorter timescale. Variability studies of edge-on disks would allow to test the dominant scenario for the origin of these asymmetries.

我们报道了嵌入型年轻恒星IRAS04302+2247周围侧视原行星盘（protoplanetary disk）的詹姆斯·韦布空间望远镜（James Webb Space Telescope, JWST）成像数据，其成像波段覆盖2μm至21μm。该天体的结构呈现为一条暗带分隔的两片反射星云。在约4.4μm及更短波长波段，天体的延展形态主要由延伸的丝状包层主导；在7μm及更长波长波段，则转变为源自原行星盘自身散射光的更为紧凑的散射叶瓣。暗带厚度随波长无显著变化，我们将这一观测特征解释为原行星盘上层存在中等尺寸（~10μm）尘埃颗粒的直接证据。值得注意的是，我们发现IRAS40302最亮的反射星云在12.8μm与21μm波段间发生了位置切换。我们探究了内区倾斜对侧视原行星盘整体外观的影响，结果表明，包含倾斜内区的原行星盘辐射转移模型（radiative transfer model）能够复现最亮反射星云的位置反转现象。此外，在特定观测取向条件下，该模型还预测了强烈的侧向不对称性，这类不对称性在超过半数的可能观测方位角下均可出现。目前通过散射光观测到的侧视原行星盘中，有15/20存在此类侧向不对称性，这提示绝大多数原行星盘可能都拥有倾斜的内区。恒星星斑（stellar spot）同样可能引发侧向不对称性，且这类不对称性的变化时标预计显著更短。对侧视原行星盘开展变异性研究，将能够检验这类不对称性起源的主导假说。