arXiv 1111.51562011-11-22astro-ph.SR

富氧AGB星的Herschel/HIFI观测：分子清单

Herschel/HIFI observations of O-rich AGB stars : molecular inventory

K. Justtanont, T. Khouri, M. Maercker, J. Alcolea, L. Decin, H. Olofsson, A. P. Marston, D. Teyssier, J. Cernicharo, C. Dominik, A. de Koter, G. Melnick, K. M. … 展开作者

K. Justtanont, T. Khouri, M. Maercker, J. Alcolea, L. Decin, H. Olofsson, A. P. Marston, D. Teyssier, J. Cernicharo, C. Dominik, A. de Koter, G. Melnick, K. M. Menten, D. Neufeld, P. Planesas, M. Schmidt, R. Szczerba, R. Waters

备注：: 6 Figures in the main paper + 12 further figures in the appendix (to be printed in electronic form) Accepted for publication by A&A
DOI：: 10.1051/0004-6361/201117524

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摘要：

本文介绍了赫歇尔空间天文台的HIFISTARS保证时间密钥计划中的富氧渐近巨星分支（AGB）星的外差光谱。该计划的目的是研究动力学结构，质量损失的驱动机制，以及从AGB星流出的化学成分和初始质量的函数。我们利用HIFI仪器对9颗AGB星进行了观测，主要观测了H_2O和高转动CO谱线，研究了谱线光度、谱线比与质量损失率、谱线宽度与激发能的相关性。总共有九种不同的分子，以及它们的一些同位素已被确定，涵盖了广泛的激发温度。在邻位和对位H2O分子中都检测到脉泽发射。正、仲H_2O的基态谱线、CO和NH_3的高J谱线的线亮度与质量损失率有明显的相关性。H2O和NH3相对于CO的线比J=6-5与质量损失率相关，而高CO线与6-5的比率与之无关。在大多数情况下，从观测到的相对靠近恒星光球层形成的高激发跃迁的线宽导出的膨胀速度低于较低激发跃迁的线宽，形成得更远，指向加速流出。在某些物体中，探测加速区的振动激发的H2O和SiO表明风已经在包络的最里面部分达到了它的终极速度，即，加速很快。有趣的是，对于R Dor，我们发现在物质已经从恒星逃逸的区域中流出减速的迹象。

英文摘要：

Spectra, taken with the heterodyne instrument, HIFI, aboard the Herschel Space Observatory, of O-rich asymptotic giant branch (AGB) stars which form part of the guaranteed time key program HIFISTARS are presented. The aim of this program is to study the dynamical structure, mass-loss driving mechanism, and chemistry of the outflows from AGB stars as a function of chemical composition and initial mass. We used the HIFI instrument to observe nine AGB stars, mainly in the H2O and high rotational CO lines We investigate the correlation between line luminosity, line ratio and mass-loss rate, line width and excitation energy. A total of nine different molecules, along with some of their isotopologues have been identified, covering a wide range of excitation temperature. Maser emission is detected in both the ortho- and para-H2O molecules. The line luminosities of ground state lines of ortho- and para-H2O, the high-J CO and NH3 lines show a clear correlation with mass-loss rate. The line ratios of H2O and NH3 relative to CO J=6-5 correlate with the mass-loss rate while ratios of higher CO lines to the 6-5 is independent of it. In most cases, the expansion velocity derived from the observed line width of highly excited transitions formed relatively close to the stellar photosphere is lower than that of lower excitation transitions, formed farther out, pointing to an accelerated outflow. In some objects, the vibrationally excited H2O and SiO which probe the acceleration zone suggests the wind reaches its terminal velocity already in the innermost part of the envelope, i.e., the acceleration is rapid. Interestingly, for R Dor we find indications of a deceleration of the outflow in the region where the material has already escaped from the star.

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