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Determination of an Instability Strip of Long Period Variables

长周期变量不稳定带的确定

基本信息

批准号：
04640266
负责人：
SHIBAHASHI Hiromoto
金额：
$ 1.41万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1992
资助国家：
日本
起止时间：
1992 至 1993
项目状态：
已结题

项目摘要

Infrared photometric investigation of Mira variables in the Large Magellanic Cloud has been extensively carried out since the late 1970s. Since stars in LMC are almost equally distant from us, we can discuss some properties of these stars by dealing with only relative luminosity without accurate knowledge of bolometric correction for absolute magnitudes. In this way, astronomers in SAAO obtained observationally a period-luminosity relation of Mira variables in LMC.In the present research project, we show that there should exist a period-mass-luminosity relation rather than a simple period-luminosity relation for Mira variables. A recent observationally obtained period-luminosity relation for these stars should be considered as a projection of the period-mass-luminosity relation on the (period, luminosity)-plane, and the scatter around an observationally fitted line of the period-luminosity relation should be interpreted partially as a mass distribution of the sample stars. We show that … More from this scatter we can deduce the mass and the position of each of the stars in the HR diagram. An observationally obtained period-luminosity relation of Mira variables implies the existence of an instability strip for these stars.We also propose a possible interpretation for the Blazhko effect in the RR Lyrae variables, which has remained to be solved for a very long time. We assume that these stars have a dipole magnetic field, which is oblique to the rotation axis of the star, and examine the effect of this field on the radial fundamental oscillation mode as a small perturbation. We demonstrate that the observed Blazhko effect is well interpreted by taking account of the perturbation to the eigenfunction. We estimate the magnetic field strength necessary to explain the Blazhko effect. This model will be justified if such magnetic fields will be detected. We also apply this model to the rapidly oscillating Ap stars. Most of Ap stars are believed to have, at least, a quadrupole magnetic field in addition to a main dipole component. In this research, we consider a general poloidal magnetic field and investigate its effect upon oscillations as a perturbation. Comparing the present results with the observational data provides us with asteroseimological information of these stars. We finally investigate the stochastic excitation mechanism of oscillations in the solar-like stars, and obtain the frequency range of the excited oscillation modes in a various stars. We expect that the semi-regular and/or irregular luminosity variation in late type stars may be a manifestation of the oscillations excited by this mechanism. Less

自1970年代末以来，对大麦哲伦星云中的Mira变星进行了广泛的红外光度研究。由于LMC中的恒星与我们的距离几乎相等，我们可以通过只处理相对光度来讨论这些恒星的一些性质，而不需要准确地了解绝对星等的测辐射热校正值。通过这种方式，SAAO的天文学家在观测上获得了LMC中Mira变星的周期-光度关系。在本研究项目中，我们证明了Mira变星应该存在周期-质量-光度关系，而不是简单的周期-光度关系。最近观测得到的这些恒星的周期-光度关系应视为周期-质量-光度关系在(周期，光度)平面上的投影，而围绕观测拟合周期-光度关系直线的散射应部分解释为样本恒星的质量分布。我们证明了…更多地，我们可以从这种散射中推断出每一颗恒星在HR图中的质量和位置。通过观测得到的Mira变星的周期-光度关系表明，这些恒星存在不稳定带。我们还对天琴座RR变星中的Blazhko效应提出了一种可能的解释，这一解释已经解决了很长一段时间。我们假设这些恒星有一个与恒星旋转轴倾斜的偶极磁场，并考察了这个磁场对径向基模的影响。我们证明，通过考虑本征函数的微扰，可以很好地解释观测到的Blazhko效应。我们估计了解释Blazhko效应所需的磁场强度。如果探测到这样的磁场，这个模型就会被证明是正确的。我们还将该模型应用于快速振荡的AP星。大多数AP星被认为，除了主偶极分量外，至少还有四极磁场。在这项研究中，我们考虑一个一般的极向磁场，并将其作为微扰来研究其对振荡的影响。将目前的结果与观测数据进行比较，为我们提供了这些恒星的恒星地震信息。最后，我们研究了类太阳恒星中振荡的随机激发机制，得到了不同恒星中激发振荡模式的频率范围。我们预计，晚型恒星的半规则和/或不规则光度变化可能是这一机制所激发的振荡的一种表现。较少