A Study of Mass-Loss from Red Giant Stars Based on Super High Resolution Optical Spectroscopy

利用冈山天体物理观测站188厘米反射镜上的HIDES光谱仪，对光学碳星的星周C_2天鹅带吸收谱线进行了快时观测。在此基础上，我们对C_2吸收线进行了系统的测量，并对C_2吸收线进行了定量分析。我们获得了44颗星的样本，其中17颗星具有明确的CS C_2线。发现在有效温度低于2800 K、C/O比大于1.1的恒星中，存在CSC_2谱线。C_2气体径向速度的测量精度可达± 20 m/s。C_2气体的旋转激发温度将气体层定位在星周区域，大约在几十到一百个恒星半径之间。CSC_2气体的丰度估计表明，CSC_2是由星际辐射场光解流出的C_2H_2形成的。CS C_2气体可能是一种新的探测中心星星半径约10^ cm区域的光学探针<15>。这也可能推导出这些恒星的碳同位素比率，类似的分析也适用于Mira型碳星。然而，我们还没有在碳星中的C_3或SiC_2等多原子分子或富氧星中的某些分子中探测到类似的CS吸收线。我们还在硅酸盐碳星星BM Gem中发现了具有P-Cyg轮廓的Balmer和Paschen连续谱发射和Balmer系列谱线。在能量学的基础上，可以一致地理解BM Gem有一个伴星的假设，该伴星产生一个加速所观察到的高速外流的吸积盘。结果表明，伴星的存在对硅酸盐碳星星现象起着重要的作用。

Circumstellar(CS) C_2 Swan band absorption lines were detected for the fast time in optical carbon stars using HIDES spectrometer on the 188cm reflector at Okayama Astrophysical Observatory. On the basis of this discovery, we have performed a systematic survey of CS C_2 absorption lines and made a quantitative analysis of the C_2 absorption lines. We have obtained a sample of 44 stars, among which 17 stars show definite CS C_2 lines. It is found that CS C_2 lines are seen in stars having effective temperature lower than 2800K and a C/O ratio greater than 1.1. A very high accuracy as high as 〜 20 m/s is achieved in radial velocity measurements of the CS C_2 gas. Rotational excitation temperature of the C_2 gas locates the gas layer in the circumstellar region, somewhere between several tens and a hundred stellar radii. Estimated abundances of the CS C_2 gas suggest that the CS C_2 form from C_2H_2 in the outflows through photo-dissociation by the interstellar radiation field. The CS C_2 gas may be a new optical probe of the region with radii of 〜10^<15> cm from the central star. It would also be possible to derive carbon isotopic ratios in these stars, and similar analyses would be applicable to Mira-type carbon stars. We have not detected, however, similar CS absorption lines by polyatomic molecules such as C_3 or SiC_2 in carbon stars or by some molecules in oxygen-rich stars. We have also discovered Balmer and Paschen continuum emission and Balmer series lines with P-Cyg profile in the silicate carbon star, BM Gem. On the basis of the energetics, the hypothesis that BM Gem has a companion that gives rise to an accretion disk that accelerates the observed high velocity outflow can be understood consistently. The results show that the existence of a companion plays an important role in the silicate carbon star phenomena.