在极端碳星IRC+10216的风中存在水已经被赫歇尔望远镜证实。高J H2O谱线被探测到的区域靠近恒星半径r \geq 15 R \ast。目的:我们研究了IRC+10216内部层中的水和相关分子的形成,在那里灰尘也会形成并加速风。方法:我们描述的分子形成的化学动力学网络,涉及碳和氧为基础的分子。然后,我们将这个网络的物理条件有关的灰尘形成区的经验之间的1和5 R \ast的脉动驱动的冲击通过。我们解决了一个系统的刚性,耦合,普通和微分方程。结果:成尘区存在非平衡化学。H2O在光球层上方快速形成,这是由热激波后气体中CO的热碎裂引起的羟基OH的合成。导出的5 R \ast处H2的丰度为1.4 \times 10-7,这与Herschel观测值非常吻合。无论恒星的C/O比如何,水的非平衡形成过程都是活跃的,因此,在渐近巨星分支上的所有恒星的风加速区都应该存在H2O。
英文摘要:
Context: The presence of water in the wind of the extreme carbon star IRC+10216 has been confirmed by the Herschel telescope. The regions where the high-J H2O lines have been detected are close to the star at radii r \geq 15 R\ast. Aims: We investigate the formation of water and related molecules in the periodically-shocked inner layers of IRC+10216 where dust also forms and accelerates the wind. Methods: We describe the molecular formation by a chemical kinetic network involving carbon-and oxygen-based molecules. We then apply this network to the physical conditions pertaining to the dust-formation zone which experiences the passage of pulsation- driven shocks between 1 and 5 R\ast. We solve for a system of stiff, coupled, ordinary, and differential equations. Results: Non-equilibrium chemistry prevails in the dust-formation zone. H2O forms quickly above the photosphere from the synthesis of hydroxyl OH induced by the thermal fragmentation of CO in the hot post-shock gas. The derived abundance with respect to H2 at 5 R\ast is 1.4\times10-7, which excellently agrees the values derived from Herschel observations. The non-equilibrium formation process of water will be active whatever the stellar C/O ratio, and H2O should then be present in the wind acceleration zone of all stars on the Asymptotic Giant Branch.
The inner wind of IRC+10216 revisited: New exotic chemistry and diagnostic for dust condensation in carbon stars
目标。我们模拟了碳星IRC+10216的内风化学,并考虑了恒星脉动引起的周期性激波对气体的影响,以遵循激波气体层中的非平衡化学。我们考虑一个非常完整的化学家族,包括碳氢化合物和芳香族化合物,卤素和含磷物种。导出的丰度进行比较,从大型调查和赫歇尔的最新观测数据。结果冲击诱导的IRC+10216的尘埃形成区的非平衡化学碰撞破坏的CO在冲击后的气体触发形成的O-轴承物种(H2O,SiO)。大多数模拟丰度与IRC+10216上Herschel数据的最新值非常吻合。氢化物形成了一个家庭的丰富的物种,被驱逐到中间包层。特别地,HF将所有原子氟捕获在尘埃形成区中。卤素也很丰富,它们的化学性质与恒星的C/O比无关。因此,HCl和其他含Cl的物种也应该存在于富O AGB或超巨星的内风中。我们确定了一个特定的区域范围从2.5 R* 到4 R*,多环芳烃的形成和增长。根据芳烃质量估算的碳尘-气体质量比范围为1.2 x 10^(-3)至5.8 x 10^{-3},与现有观测值吻合良好。芳族化合物形成区域位于热层的外部,其中SiC 2作为碳化硅粉尘合成的副产物产生。最后,我们预测一些分子线将显示通量随脉动相位和时间的变化(例如,H2O),而其他物种则不会(例如,CO)。这些变化仅仅反映了在尘埃形成区的冲击气体中在脉动周期内破坏和重整分子的非平衡化学。
Charting circumstellar chemistry of carbon-rich asymptotic giant branch stars. II. Abundances and spatial distributions of CS
Chalmers University of Technology(查尔姆斯理工大学);Uppsala University(乌普萨拉大学);Joint ALMA Observatory(ALMA联合天文台);European Southern Observatory(欧洲南方天文台);Leiden University(莱顿大学);Monash University(蒙纳士大学);KU Leuven(荷语鲁汶大学);Queen’s University Belfast(贝尔法斯特女王大学);NASA Goddard Space Flight Center(NASA戈达德太空飞行中心);Gemini Observatory(双子座天文台)
Charting circumstellar chemistry of carbon-rich asymptotic giant branch stars. III. SiO and SiS abundances
Chalmers University of Technology(查尔姆斯理工大学);Joint ALMA Observatory(ALMA联合 observatory);European Southern Observatory(欧洲南方天文台);Leiden University(莱顿大学);Queen’s University Belfast(贝尔法斯特女王大学)
The impact of surface acetylene cyclotrimerization on the abundance of aromatic hydrocarbons in carbon-rich asymptotic giant branch stars
Institute of Astronomy of Russian Academy of Sciences(俄罗斯科学院天文学研究所);Lomonosov Moscow State University(莫斯科国立罗蒙诺索夫大学);Skolkovo Institute of Science and Technology(斯科尔科沃科学技术学院);Samara Branch of P. N. Lebedev Physical Institute of the Russian Academy of Sciences(俄罗斯科学院列别杰夫物理研究所萨马拉分部);Ural Federal University(乌拉尔联邦大学)
Host--Non-host Differences in Stellar Chemistry, Activity, and Birth Radius: Hints of Distinct Formation Environments for Earth-like Planets and Sub-Neptunes
School of Science, Hangzhou Dianzi University(杭州电子科技大学理学院);National Astronomical Data Center Zhijiang Branch(国家天文台数据科学中心(紫金山));CAS Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences(中国科学院国家天文台光学天文重点实验室);Department of Astronomy, The Ohio State University(俄亥俄州立大学天文学系);Center for Cosmology and Astroparticle Physics (CCAPP), The Ohio State University(俄亥俄州立大学宇宙学与高能物理中心);Department of Physics, Xiangtan University(湘潭大学物理系);School of Physics and Astronomy, Beijing Normal University(北京师范大学物理与天文学院)