钡星重元素丰度的再研究

A Re-analysis of the Heavy-Element Abundance of Barium Stars

在包括双星及逃逸物质的系统总角动量守恒模型的基础上，采用星风质量吸积机制，由伴星通过逐次脉冲从主星吸积物质并与其外包层进行混合的模型出发，自洽地计算了钡星的重元素超丰，并给出理论计算结果与观测值的比较．计算结果表明，当取Ｂｏｎｄｉ－Ｈｏｙｌｅ质量吸积率的五分之一作为实际吸积率时，对于轨道周期较长（Ｐ＞１６００天）、相距较远的钡星系统，在误差范围内，理论计算曲线与大多数样品星的重元素丰度观测值相符合；而对于ＨＤ２０４０７５和ＨＤ１６４５８两颗钡星，将质量吸积率增大为Ｂｏｎｄｉ－Ｈｏｙｌｅ质量吸积率的二分之一时，计算结果与观测值符合较好，这表明质量吸积率在Ｂｏｎｄｉ－Ｈｏｙｌｅ质量吸积率的十分之一至二分之一之间．对于具有较短轨道周期（Ｐ＜６００天）的钡星系统，计算结果与丰度观测值偏差较大，表明钡星系统中还有其它的形成机制．

n the basis of conservation of total angular momentum in a binary system includingescaping matter, we adopt a model in which the companion star accretes matter from themain star through successive pulses with mixing in its outer envelope. From a self-consistedscalculation of the heavy element overabundance of barium stars, it is found that, for anactual accretion rate equal to 1/5 the Bondi-Hoyle accretion rate, the calculated curvesagree with the observed overabundances in a majority of barium systems with long orbitalperiods (P >1600 d), while for two stairs, HD 20405 and HD 16458, agreement is obtained ifthe accretion rate is increased to 1/2 the Bondi-Hoyle Value. This indicates that the actualaccretion rate is between 0.1-0.5 the Bondi--Hoyle rate. For short period (P < 600d) stars,the agreement is not good. Thus, wind accretion appears plausible for barium stars withlonger periods, while for the shorter period barium stars some other mechanism may be atwork.