arXiv 1709.047382017-09-14astro-ph.GA

IRC +10 216的3-D：TP-AGB星包层的形态

IRC +10 216 in 3-D: morphology of a TP-AGB star envelope

M. Guélin, N. A. Patel, M. Bremer, J. Cernicharo, A. Castro-Carrizo, J. Pety, J. P. Fonfría, M. Agúndez, M. Santander-García, G. Quintana-Lacaci, L. Velilla Pri… 展开作者

M. Guélin, N. A. Patel, M. Bremer, J. Cernicharo, A. Castro-Carrizo, J. Pety, J. P. Fonfría, M. Agúndez, M. Santander-García, G. Quintana-Lacaci, L. Velilla Prieto, R. Blundell, P. Thaddeus

备注：: 22 pages, 28 figures. Accepted for publication in A&A
发表信息：: A&A 610, A4 (2018)
DOI：: 10.1051/0004-6361/201731619

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摘要：

在脉动阶段的后期，AGB恒星以大质量尘埃包层的形式排出大部分质量，这一事件在很大程度上控制了星际物质的组成。然而，这些包层距离遥远，对可见光和近红外辐射不透明：它们的结构仍然知之甚少，质量损失过程也知之甚少。毫米波干涉测量法是这方面的最佳调查工具。星周包层IRC +10 216和它的中心恒星，离太阳最近的富碳TP-AGB星，是进行这种研究的最佳对象。两年前，我们报道了IRAM 30米望远镜在该包层（HPBW 11”）中的CO（2-1）线发射观测。我们现在报告用SMA、PdB和ALMA干涉仪（合成半功率波束宽度分别为3”、1”和0.3”）对CO（2-1）、CO（1-0）、CN（2-1）和C $_4$ H（24-23）进行的高得多的角分辨率观测。虽然在高分辨率下，它的外壳看起来更加复杂，但它的主要结构仍然是薄的，几乎同心的外壳。在小的尘埃形成区（r<0.3”）之外，气体似乎以14.5 km/s的恒定速度径向膨胀，并伴有小的湍流运动。根据这一性质，我们重建了外包层的三维结构，导出了内包层（r<25”）气体温度和密度的径向分布。过密壳具有球形或略扁的形状，并且通常延伸超过几个球面度，这意味着各向同性的质量损失。外层包层中规则的壳层间距支持一个周期为700年的双星系统和一个近面对面的椭圆轨道模型。伴星的飞越触发了近星点附近质量损失的增强事件。在包层中心部分观察到的贝壳图案的致密化表明了过去几千年来更复杂的情况。

英文摘要：

During their late pulsating phase, AGB stars expel most of their mass in the form of massive dusty envelopes, an event that largely controls the composition of interstellar matter. The envelopes, however, are distant and opaque to visible and NIR radiation: Their structure remains poorly known and the mass-loss process poorly understood. Millimeter-wave interferometry is the optimal investigative tool for this purpose. The circumstellar envelope IRC +10 216 and its central star, the C-rich TP-AGB star closest to the Sun, are the best objects for such an investigation. Two years ago, we reported on IRAM 30-m telescope CO(2-1) line emission observations in that envelope (HPBW 11"). We now report much higher angular resolution observations of CO(2-1), CO(1-0), CN(2-1) and C$_4$H(24-23) made with the SMA, PdB and ALMA interferometers (with synthesized half-power beamwidths of 3", 1" and 0.3", respectively). Although the envelope appears more intricate at high resolution, its prevailing structure remains a pattern of thin, nearly concentric shells. Outside the small (r<0.3") dust formation zone, the gas appears to expand radially at a constant velocity, 14.5 km/s, with small turbulent motions. Based on that property, we have reconstructed the 3-D structure of the outer envelope and have derived the gas temperature and density radial profiles in the inner (r<25") envelope. The over-dense shells have spherical or slightly oblate shapes and typically extend over a few steradians, implying isotropic mass loss. The regular spacing of shells in the outer envelope supports the model of a binary star system with a period of 700 years and a near face-on elliptical orbit. The companion fly-by triggers enhanced episodes of mass loss near periastron. The densification of the shell pattern observed in the central part of the envelope suggests a more complex scenario for the last few thousand years.

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