中国科学院云南天文台机构知识库

转动和潮汐效应是影响恒星结构和演化的非常重要的物理因素. 根据对Achernar的观测数据, 用扰动理论推导了临界转动恒星Achernar分别作为单星和双星的斜压结构的特征, 给出Achernar等压面上的密度等物理量的分布. 利用考虑转动和潮汐及形变效应的单、双星模型研究了Achernar的引力昏暗现象. 结果表明正剪切增强离心力、减小赤道的重力加速度和温度, 反剪切结果则与之相反. 反剪切和刚性转动情况并不符合对Achernar的引力昏暗观测结果. 发现转动双星模型比单星模型虽更符合Achernar赤道和极半径之比的观测值, 但理论计算的角速度比观测值小. 对比理论计算和观测结果发现, 当Achernar的自转角速度为4.65× 10^-5 s^-1, 正剪切率Ω/Ω_s为0.7851时, Achernar的极点温度为16041 K, 赤道温度为12073 K. 所有理论计算与观测值的相对误差不超过7%.

Rotation and tide are two important factors that have very important impacts on the stellar structure and evolution. Based on the observational data ofAchernar, we have derived the inclined pressure structure in a single rotating star or as a member in the binaries. We have given the distributions of thephysical quantities on the isobaric surface and these distributions are derived from the Legendre series of expansions. We have also found the relationship between all levels of perturbation potential functions (including rotational and tidal distortions) and the distributions of density and pressure under thecondition of inclined pressure structure. In particular, the gravitational darkening with the models including the effects of rotation and tide is investigated. We have found that the critical ratio of equatorial radius to the polar radius is consistent with the observations in rotating binaries better than that in single rotating model. The reason is that the tidal force can make the polar radius shortened because the tidal force exerts an inward force to the two polar points. However, the theoretical angular velocity in binaries is smaller than that observed. It is also shown that the positive shear enhances the centrifugal force and decreases the mean effective gravitational acceleration and effective temperatures whereas the negative shear plays a role to strengthen the effective gravitational acceleration. Moreover, the solid body rotation has not been supported inside Achernar because magnetic fields have not been detected through observations. Furthermore, the theoretical angular velocity in rigid rotation is higher than the angular velocity observed. Achernar has a periodic variation of light curves due to mass outburst, which also supports differential rotation. A positive shear indicates that the mass in accretion disks is falling to Achernar and the Achernar is spun up to critical rotation according to current observations. By comparing the theoretical results with observations, it can be seen that when the theoretical spin angular velocity of Achernar is 4.65 x 10(-5) s(-1) and the positive shears Omega/Omega(s) are 0.7851, the temperature ofthe polar points is 16041 K and that of equatorial sphere is 12073 K. Relative errors between the theoretical values and observations are less than 3% and are listed in the text. This model is the best and is the most possible one for Achernar.