论文标题
O富含AGB恒星的O富集式中的S-和Si含量分子的丰度
The abundance of S- and Si-bearing molecules in O-rich circumstellar envelopes of AGB stars
论文作者
论文摘要
目的：我们旨在确定SIO，CS，SIS，SO和SO $ _2 $的丰富性在大量富含氧气的AGB信封中，涵盖了广泛的质量损失率，以研究这些分子在这些环境中可以在灰尘形成中起的潜在作用。 方法：我们使用IRAM 3000万望远镜调查了$λ$ 2毫米带中30个富含氧气的AGB星的样品。我们基于LVG方法进行了激发和辐射转移计算，以模拟观察到的分子线，并在观察到的信封中得出它们的分数丰度。 结果：我们分别在18、13、26和19来源中检测到所有30个目标信封以及CS，SIS，SO和SO $ _2 $的SIO。值得注意的是，在任何信封中未检测到SIS，其质量损失率低于$ 10^{ - 6} $ M $ _ {\ odot} $ yr $^{ - 1} $，而在所有信封中都检测到具有高于该阈值的质量损失率。从与以前关于富含C的富源的类似研究的比较，很明显，CS和SIS的分数丰富性在C富含C和O的富源源之间显示出明显的差异，分别是两个数量级和一个数量级，并且在C富含C的源中更丰富，而SIO的cio源则是COIO的分数，而cs sio的分数则是实用的。 O富集信封中的Sio丰富性与C富源的来源相似，即信封的密集，其丰度越低。在O富集的来源中，观察到SO的类似趋势，尽管不如SIO清楚。 结论：CS和SIS丰度对C/O比的明显依赖性表明，这两个分子在C-中比O-o-o-富构封发更有效。 SIO的丰度随着包膜密度的增加而下降，暂定的暂定表明SIO，并且可能充当了围绕O富含O的AGB恒星的壳信封中尘埃的气相前体。
Aims: We aim to determine the abundances of SiO, CS, SiS, SO, and SO$_2$ in a large sample of oxygen-rich AGB envelopes covering a wide range of mass loss rates to investigate the potential role that these molecules could play in the formation of dust in these environments. Methods:We surveyed a sample of 30 oxygen-rich AGB stars in the $λ$ 2 mm band using the IRAM 30m telescope. We performed excitation and radiative transfer calculations based on the LVG method to model the observed lines of the molecules and to derive their fractional abundances in the observed envelopes. Results:We detected SiO in all 30 targeted envelopes, as well as CS, SiS, SO, and SO$_2$ in 18, 13, 26, and 19 sources, respectively. Remarkably, SiS is not detected in any envelope with a mass loss rate below $10^{-6}$ M$_{\odot}$ yr$^{-1}$, whereas it is detected in all envelopes with mass loss rates above that threshold. From a comparison with a previous, similar study on C-rich sources, it becomes evident that the fractional abundances of CS and SiS show a marked differentiation between C-rich and O-rich sources, being two orders of magnitude and one order of magnitude more abundant in C-rich sources, respectively, while the fractional abundance of SiO turns out to be insensitive to the C/O ratio. The abundance of SiO in O-rich envelopes behaves similarly to C-rich sources, that is, the denser the envelope the lower its abundance. A similar trend, albeit less clear than for SiO, is observed for SO in O-rich sources. Conclusions: The marked dependence of CS and SiS abundances on the C/O ratio indicates that these two molecules form more efficiently in C- than O-rich envelopes. The decline in the abundance of SiO with increasing envelope density and the tentative one for SO indicate that SiO and possibly SO act as gas-phase precursors of dust in circumstellar envelopes around O-rich AGB stars.
