追踪碳星CIT 6周围包层的不对称性
Tracing the asymmetry in the envelope around the carbon star CIT 6
摘要：
本文报道了极碳星CIT 6的HC $_3$ NJ =5- 4谱线和7 mm连续谱线的高角分辨率观测结果。我们发现，7毫米的连续发射是未解决的，并具有一致的黑体热辐射从中央恒星的通量。HC $_3$ N J=5- 4线发射起源于一个不对称的、团状的膨胀包层，它包括两个分离的HC $_3$ N J=5- 4发射壳层：（i）一个半径为8 \arcsec的近球形暗外壳层;及（ii）一个厚而不完整的内壳，而该内壳类似─臂螺旋从中心星或靠近中心星开始并向外延伸到大约5 \arcsec的半径。因此，我们的观察结果表明，CIT 6的质量损失是强烈调制的时间和高度各向异性。此外，数据和我们的激发建模结果之间的比较表明，HC $_3$ N在其包络线中的丰度异常高。我们讨论的可能性，信封可能是由先前建议的可能的二进制伴侣的存在下形成的。HC $_3$ N的丰度可能在CIT 6星周包层与其伴星相互作用产生的螺旋激波中增强。
英文摘要：
We present high angular resolution observations of HC$_3$N J=5--4 line and 7 mm continumm emission from the extreme carbon star CIT 6. We find that the 7 mm continuum emission is unresolved and has a flux consistent with black-body thermal radiation from the central star. The HC$_3$N J=5--4 line emission originates from an asymmetric and clumpy expanding envelope comprising two separate shells of HC$_3$N J=5--4 emission: (i) a faint outer shell that is nearly spherical which has a radius of 8\arcsec; and (ii) a thick and incomplete inner shell that resembles a one-arm spiral starting at or close to the central star and extending out to a radius of about 5\arcsec. Our observations therefore suggest that the mass loss from CIT 6 is strongly modulated with time and highly anisotropic. Furthermore, a comparison between the data and our excitation modelling results suggests an unusually high abundance of HC$_3$N in its envelope. We discuss the possibility that the envelope might be shaped by the presence of a previously suggested possible binary companion. The abundance of HC$_3$N may be enhanced in spiral shocks produced by the interaction between the circumstellar envelope of CIT 6 and its companion star.
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