近日，西班牙Instituto de Física Fundamental的J.Cernicharo及其研究小组取得一项新进展，经过不懈努力，他们发现大气分子团形成了AGB恒星的星周包层。相关研究成果已于2023年5月17日在国际权威学术期刊《自然》上发表。

该研究报道了对IRC+10°216大气中新形成的尘埃和分子气体的观测结果，其分辨率达到一个恒星半径。研究人员观察到HCN、SiS和SiC₂的谱线在不同的半径和云团中出现，他们将这些现象解释为光球中的大尺度对流单体，类似于参宿四星的情况。这些对流单体随着脉冲的发生而聚合，导致了各向异性的现象，并与伴星一起共同塑造了星周包层。

据介绍，在热脉冲阶段，渐近巨星支（AGB）恒星会喷射出形成扩展尘埃包层的物质。可见光偏振成像发现几颗富氧恒星的两倍恒星半径内存在颗粒状尘埃云团。同时，对于WHya、Mira等不同的富氧恒星，也在其几倍恒星半径内的多个发射线中观测到非均匀的分子气体。在恒星表面水平，红外图像显示碳半规则可变恒星R Scl和S型恒星π¹Gru周围存在复杂结构。此外，红外图像还揭示了典型AGB碳星IRC+10°216的几倍恒星半径内的颗粒状尘埃结构，并且对超出尘埃形成区的分子气体分布的研究也显示了其复杂的星周结构。然而，由于空间分辨率不足，他们还尚不了解AGB碳星的恒星大气和尘埃形成区内分子气体的分布情况，以及它们是如何随后被排出的。

附：英文原文

Title: Atmospheric molecular blobs shape up circumstellar envelopes of AGB stars

Author: Velilla-Prieto, L., Fonfra, J. P., Agndez, M., Castro-Carrizo, A., Gulin, M., Quintana-Lacaci, G., Cherchneff, I., Joblin, C., McCarthy, M. C., Martn-Gago, J. A., Cernicharo, J.

Issue&Volume: 2023-05-17

Abstract: During their thermally pulsing phase, asymptotic giant branch (AGB) stars eject material that forms extended dusty envelopes¹. Visible polarimetric imaging found clumpy dust clouds within two stellar radii of several oxygen-rich stars^2,3,4,5,6. Inhomogeneous molecular gas has also been observed in multiple emission lines within several stellar radii of different oxygen-rich stars, including WHya and Mira^7,8,9,10. At the stellar surface level, infrared images have shown intricate structures around the carbon semiregular variable RScl and in the S-type star π¹Gru^11,12. Infrared images have also shown clumpy dust structures within a few stellar radii of the prototypical carbon AGB star IRC+10°216 (refs. ^13,14), and studies of molecular gas distribution beyond the dust formation zone have also shown complex circumstellar structures¹⁵. Because of the lack of sufficient spatial resolution, however, the distribution of molecular gas in the stellar atmosphere and the dust formation zone of AGB carbon stars is not known, nor is how it is subsequently expelled. Here we report observations with a resolution of one stellar radius of the recently formed dust and molecular gas in the atmosphere of IRC+10°2¹⁶. Lines of HCN, SiS and SiC₂ appear at different radii and in different clumps, which we interpret as large convective cells in the photosphere, as seen in Betelgeuse¹⁶. The convective cells coalesce with pulsation, causing anisotropies that, together with companions^17,18, shape its circumstellar envelope.

DOI: 10.1038/s41586-023-05917-9

Source: https://www.nature.com/articles/s41586-023-05917-9