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 cm反射镜上的HIDES光谱仪，对光学碳星的(CS)C_2天鹅带吸收线进行了快速测量。在此基础上，我们对CS C_2吸收谱线进行了系统的测量，并对C_2吸收谱线进行了定量分析。我们已经获得了44颗恒星的样本，其中17颗恒星有明确的CS C_2线。结果表明，在有效温度低于2800K、C/O比大于1.1的恒星中存在CSC2谱线。在CS-C2气体径向速度测量中，获得了高达~20m/S的高精度。C2气体的转动激发温度位于星周区域的气体层，在几十到一百个恒星半径之间。CS C_2气体丰度的估算表明，CS C_2是由外流中的C_2H_2在星际辐射场的光解作用下形成的。CS C_2气体可能是该区域的一种新的光学探头，其半径为距中星约10^~15&gt；cm。还有可能得出这些恒星中的碳同位素比率，类似的分析也适用于米拉类型的碳星。然而，我们还没有探测到碳星中的C_3或SiC_2等多原子分子或富氧星中的某些分子的类似CS吸收线。我们还在硅酸盐碳星BM Gem中发现了具有P-Cyg轮廓的Balmer和Paschen连续发射谱线和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，它会产生一个加速观测到的高速外流的吸积盘。结果表明，伴星的存在在硅酸盐碳星现象中起着重要作用。

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.