High-resolution HST/ACS images of detached shells around carbon stars
High-resolution HST/ACS images of detached shells around carbon stars
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碳星周围分离壳的高分辨率 HST/ACS 图像
DOI：
10.1051/0004-6361/200913929
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发表时间：
2010
影响因子：
6.5
通讯作者：
F. Schöier
中科院分区：
文献类型：
--
作者：
H. Olofsson;H. Olofsson;M. Maercker;Kjell Eriksson;Bengt Gustafsson;F. Schöier
上下文。在一些渐近巨支（AGB）碳星周围发现了整体球对称、几何上薄的气体和尘埃壳。它们的动力年龄在10(3)~ 10(4)年之间。对它们存在的一种暂定解释是，它们是在氦壳层闪光期间质量损失率调制的结果。目标。由于没有明显的视线混乱，分离的壳携带着它们形成过程的信息，以及AGB恒星周围的星周介质的小尺度结构。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详细的研究。定量结果是在假设光薄尘埃散射的情况下得出的。结果。rscl和U Cam周围的分离尘壳被发现与整体的球形对称一致。它们的半径是19 "。2（对应于8 × 10（16）厘米的线性尺寸）和7 " .7（5 × 10（16）厘米），宽度为1 " .2（5 × 10（15）厘米）和0 " .6（4 × 10(15) cm），尘埃质量分别为3 × 10（-6）和3 × 10(-7) m -圆点。R - Scl和U - Cam壳层的动力年龄分别为1700年和700年，壳层宽度分别对应100年和50年的时间尺度。在R Scl壳的图像中，可以清楚地看到小于圆弧大小的团块形式的小规模结构。估计平均团块尘埃质量约为2 × 10(-9) m圆点。与CO线干涉仪数据的比较表明，尘埃和气体壳在空间上重合，在误差范围内（U Cam <= 1”，R Scl接近2”）。结论。这些结果与氦壳闪动期间积聚损失喷发形成的几何薄气体和尘埃壳的解释一致，并且与先前的风的相互作用也起作用。造成贝壳的质量损失一定是显著的各向同性，如果风的相互作用起了作用，这也适用于喷发前的质量损失。团块结构存在于rscl壳层中，可能是质量损失本身的结果，但更可能是膨胀壳层不稳定的结果。
Context. Overall spherically symmetric, geometrically thin gas and dust shells have been found around a handful of asymptotic giant branch (AGB) carbon stars. Their dynamical ages lie in the range of 10(3) to 10(4) years. A tentative explanation for their existence is that they have formed as a consequence of mass-loss-rate modulations during a He-shell flash. 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 8 x 10(16) cm) and 7 ''.7 (5 x 10(16) cm), widths of 1 ''.2 (5 x 10(15) cm) and 0 ''.6 (4 x 10(15) cm), and dust masses of 3 x 10(-6) and 3 x 10(-7) M-circle dot, 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 2 x 10(-9) M-circle dot. Comparisons with CO line interferometer data show that the dust and gas shells coincide spatially, within the errors (<= 1 '' for U Cam and approximate to 2 '' for R Scl). Conclusions. The results are consistent with the interpretation of geometrically thin gas and dust shells formed by amass-loss eruption during a He-shell flash, and where interaction with a previous wind plays a role as well. The mass loss responsible for the shells must have been remarkably isotropic, and, if wind interaction plays a role, this also applies to the mass loss prior to the eruption. 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.