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arXiv 1003.3134astro-ph.SR
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共生恒星系统的CO观测

CO observations of symbiotic stellar systems

V. Bujarrabal, J. Mikolajewska, J. Alcolea, G. Quintana-Lacaci

摘要:

我们用IRAM 30米望远镜对共生星R Aqr、CH Cyg和HM Sge的12 CO J=2 - 1和J = 1-0、13 CO J=2-1和J=1-0以及SiO J=5-4跃迁进行了毫米波观测。通过对冷恒星周围内壳层分子发射的一般性质进行简单的分析描述,对数据进行了分析。考虑到在这种条件下的能级布居和辐射转移,还对预期的谱线轮廓进行了数值计算。在R Aqr和CH Cyg中检测到12 CO J=2-1和J=1-0的弱发射,在R Aqr中获得了良好的12 CO J=2-1谱线轮廓。探测到的谱线的强度和轮廓形状与来自米拉型恒星周围非常小的壳层的发射相兼容,其半径相当于或略小于到热矮星伴星的距离,10 $^{14}$ - 2 10 $^{14}$ cm。我们认为其他可能的解释是不可能的。这个区域可能显示出与标准AGB星周围的内壳层相似的特性:向外膨胀速度约为5 ~ 25 km/s,气体加速显著,温度随半径在1000 ~ 500 K之间降低,密度约为10 $^9$ - 3 10 $^8$ cm $^{-3}$。我们的模型计算能够解释从R Aqr在12 CO J=2-1中观察到的不对称线形,其中相对较弱的红色部分的轮廓将导致由外层的自吸收(在存在的速度增加和温度随半径降低)。质量损失率比标准的AGB星稍大,这是共生系统经常发生的情况。在R Aqr中,我们发现CO排放区的总质量为~ 2 - 3 × 10 $^{-5}$ Mo,相当于M' ~ 5 × 10 $^{-6}$ - 10 $^{-5}$ Mo/yr,与尘埃排放的结果一致。考虑到其他现有的数据分子发射,我们认为,在共生系统中的分子丰富的气体的小范围内,主要是由于分子的光离解的热矮星的辐射。

英文摘要:

We have performed mm-wave observations with the IRAM 30m telescope of the 12CO J=2-1 and J=1-0, 13CO J=2-1 and J=1-0, and SiO J=5-4 transitions in the symbiotic stars R Aqr, CH Cyg, and HM Sge. The data were analyzed by means of a simple analytical description of the general properties of molecular emission from the inner shells around the cool star. Numerical calculations of the expected line profiles, taking into account the level population and radiative transfer under such conditions, were also performed. Weak emission of 12CO J=2-1 and J=1-0 was detected in R Aqr and CH Cyg; a good line profile of 12CO J=2-1 in R Aqr was obtained. The intensities and profile shapes of the detected lines are compatible with emission coming from a very small shell around the Mira-type star, with a radius comparable to or slightly smaller than the distance to the hot dwarf companion, 10$^{14}$ - 2 10$^{14}$ cm. We argue that other possible explanations are improbable. This region probably shows properties similar to those characteristic of the inner shells around standard AGB stars: outwards expansion at about 5 - 25 km/s, with a significant acceleration of the gas, temperatures decreasing with radius between about 1000 and 500 K, and densities ~ 10$^9$ - 3 10$^8$ cm$^{-3}$. Our model calculations are able to explain the asymmetric line shape observed in 12CO J=2-1 from R Aqr, in which the relatively weaker red part of the profile would result from selfabsorption by the outer layers (in the presence of a velocity increase and a temperature decrease with radius). The mass-loss rates are somewhat larger than in standard AGB stars, as often happens for symbiotic systems. In R Aqr, we find that the total mass of the CO emitting region is ~ 2 - 3 10$^{-5}$ Mo, corresponding to M' ~ 5 10$^{-6}$ - 10$^{-5}$ Mo/yr, and compatible with results obtained from dust emission. Taking into account other existing data on molecular emission, we suggest that the small extent of the molecule-rich gas in symbiotic systems is mainly due to molecule photodissociation by the radiation of the hot dwarf star.

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