对OH/IR星演化的模型研究

渐近巨星分支恒星 (AGB星 )是一种晚期演化恒星 ,它是恒星作为以核反应释能为发光能源的天体的最后演化阶段。AGB星阶段的恒星具有许多有趣的性质 ,如很大的质量损失率 (因此形成很厚的拱星尘埃气体包层 ) ,光变 ,热脉动 (或He闪耀 ) ,强的红外超量发射 ,分子脉泽发射等 ,弄清AGB星的演化规律是研究恒星演化理论的重要任务。目前人们所知道的AGB星的演化图景是 ,恒星经过漫长的主序演化之后 ,将经过红巨星 (RGB)阶段 ,然后才进入AGB阶段 ,在其演化过程中AGB星的光度和质量损失率要逐渐增大 ,它的光变周期也逐渐变长 ,在其中心星经历了一系列的由He核反应不稳定性引起的热脉动之后 ,它的质量损失很快停止 ,恒星开始向行星状星云 (PN)演化 ,最后行星状星云将会变成一个白矮星 ,这将是许多初始质量不很大的恒星的最终结局。OH/IR星阶段是AGB星演化的一个阶段 ,OH/IR星是那些质量稍大的恒星在AGB阶段后期演化而成的天体。现阶段人们对OH/IR星的具体演化过程还知道得很少。我们利用了球对称包层中的尘埃辐射转移模型来研究OH/IR星的演化性质 ,并且收集了尽量多的具有可靠距离的OH/IR星来研究他们的光度和质量损失率的演化性质。在本文的研究工作中 ,我们主要讨论了OH/IR星在远红外双色图中的分布规律 ,还发现

Study on Evolution of OH/IR Star by Modelling

AGB phase is the last evolutionary stage in the lifetime of a nuclear energy supported star.Many interesting processes such as thermal pulse,periodically varibility caused by pulsating,large mass lose rate,strong infrared excess,molecular maser etc.,occur on the AGB stars.Astronomers have casted a great amount of concerning on the evolutionary property of AGB stars in the past decades.As we have known,AGB stars will experience a set of so called Thermal Pulses and its mean luminosity and mean mass loss rate both increase,then,after the stopping of Thermal Pulse and mass loss,they will begin to evolve towards Planetary Nebulae.But we are still not aware much of the details of AGB evolution.In the past,astronomers used many indirect methods to study the AGB evolution,and succeeded to find some overall properties of the evolution process.Now we have accomplished a huge amount of model calculations to study the property of the radiation from the envelope of OH/IR stars,a special evolutionary stage of AGB.And more importantly,we have collected 21 OH/IR stars with good-quality phase-lag distance to study the evolutionary property of their luminosity and mass loss rate.In our study,besides the comformity of double shell stage of OH/IR star evolution,we also find that a OH/IR star well appear as a non-thermal-pulse star in the early part of the OH/IR stage,and then it will step into the Thermal Pulse phase at a period of about 600 days accompanying with a sudden dramatic drop of its luminosity and mass loss rate at the very beginning of the first thermal pulse.We have tried to attribute the sudden drop of luminosity and mass loss rate to the destroy of the H burning layer in the center star by the thermal pulse and the destroyed H burning layer can never recover to its thermal pulse free status. Our study may have opened a new gate into the research work on the detailed evolution process of OH/IR stars.