碳星周围分离壳层的高分辨率HST/ACS图像
High-resolution HST/ACS images of detached shells around carbon stars
摘要：
目的：分离的壳层携带着它们形成过程的信息，以及由于没有明显的视线混淆而导致的AGB恒星周围星周介质的小尺度结构。研究方法：最年轻的分离壳，那些围绕碳星R Scl和U Cam的壳，在这里用哈勃太空望远镜上的高级巡天相机在散射的恒星光中进行了非常详细的研究。定量结果推导出假设光学薄尘埃散射。结果：发现R Scl和U Cam周围的分离尘埃壳与整体球形对称一致。它们的半径分别为19.2”（对应于8x10^16厘米）和7.7”（5x10^16厘米），宽度分别为1.2”（5x10^15厘米）和0.6”（4x10^15厘米），尘埃质量分别为3x 10 ^-6和3x 10 ^-7 M（太阳）。的R Scl和U凸轮壳的动力学年龄估计分别为1700年和700年，壳宽对应的时间尺度分别为100年和50年。在R Scl壳层的图像中可以清楚地看到小于角秒大小的团块形式的小尺度结构。团状尘埃的平均质量估计约为2x 10 ^-9 M（太阳）。与CO线干涉仪数据的比较表明，尘埃和气体壳层在空间上一致，误差范围（U凸轮<=1”，约为1“）。R Scl为2”）。结论：结果是一致的几何薄的气体和尘埃壳的解释形成的质量损失喷发在He壳闪光，并在与以前的风的相互作用发挥了作用。星团结构存在于R Scl壳层中，可能是质量损失本身的结果，但更可能是膨胀壳层中不稳定性的结果。
英文摘要：
Aims: The detached shells carry information on their formation process, as well as on the small-scale structure of the circumstellar medium around AGB stars due to the absence of significant line-of-sight confusion. Methods: The youngest detached shells, those around the carbon stars R Scl and U Cam, are studied here in great detail in scattered stellar light with the Advanced Survey Camera on the Hubble Space Telescope. Quantitative results are derived assuming optically thin dust scattering. Results: The detached dust shells around R Scl and U Cam are found to be consistent with an overall spherical symmetry. They have radii of 19.2" (corresponding to a linear size of 8x10^16 cm) and 7.7" (5x10^16 cm), widths of 1.2" (5x10^15 cm) and 0.6" (4x10^15 cm), and dust masses of 3x10^-6 and 3x10^-7 M(Sun), respectively. The dynamical ages of the R Scl and U Cam shells are estimated to be 1700 and 700 yr, respectively, and the shell widths correspond to time scales of 100 and 50 yr, respectively. Small-scale structure in the form of less than arcsec-sized clumps is clearly seen in the images of the R Scl shell. Average clump dust masses are estimated to be about 2x10^-9 M(Sun). Comparisons with CO line interferometer data show that the dust and gas shells coincide spatially, within the errors (<=1" for U Cam and approx. 2" for R Scl). Conclusions: The results are consistent with the interpretation of geometrically thin gas and dust shells formed by a mass-loss eruption during a He-shell flash, and where interaction with a previous wind plays a role as well. Clumpy structure is present in the R Scl shell, possibly as a consequence of the mass loss itself, but more likely as a consequence of instabilities in the expanding shell.
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