一种检验亚矮星B星不同形成通道的地震方法
A seismic approach to testing different formation channels of subdwarf B stars
摘要：
在亚矮星B星的形成过程中有许多未知数。不同的形成通道被认为是可能的，并导致各种氦燃烧的次矮星。然而，到目前为止，所有的地震模型都假设亚矮星B是一个氦闪后的核心，周围环绕着一层薄薄的惰性氢层。我们研究了另一个形成通道，其中亚矮星B星起源于一个大质量（>~2 Msun）的红巨星，具有非简并的氦核。虽然这些次矮星可能演化通过与典型闪后次矮星相同的log g-Teff图区域，但它们的内部结构却相当不同。我们研究这种差异如何影响它们的脉动模式，以及是否可以观察到。利用详细的恒星演化计算，我们从这两个形成通道构建了亚矮星B模型。由于扩散，导致模式的激发，在驱动区域中的铁积累，近似由高斯函数。脉动模式和频率的计算与非绝热脉动代码。详细比较了来自不同通道的两个亚矮星B模型，但具有相同的log g和Teff，表明它们的模式激发是不同的。激发频率低于后闪光比后非简并亚矮星B星。这主要是由于恒星外壳的化学成分不同。两个模型网格之间的更一般的比较表明，大多数后非简并次矮星的激发频率不能很好地匹配后闪光次矮星的频率。在找到可接受的地震匹配的罕见情况下，附加信息，例如模式识别和log g和Teff确定，允许我们区分两个地层通道。
英文摘要：
There are many unknowns in the formation of subdwarf B stars. Different formation channels are considered to be possible and to lead to a variety of helium-burning subdwarfs. All seismic models to date, however, assume that a subdwarf B star is a post-helium-flash-core surrounded by a thin inert layer of hydrogen. We examine an alternative formation channel, in which the subdwarf B star originates from a massive (>~2 Msun) red giant with a non-degenerate helium-core. Although these subdwarfs may evolve through the same region of the log g-Teff diagram as the canonical post-flash subdwarfs, their interior structure is rather different. We examine how this difference affects their pulsation modes and whether it can be observed. Using detailed stellar evolution calculations we construct subdwarf B models from both formation channels. The iron accumulation in the driving region due to diffusion, which causes the excitation of the modes, is approximated by a Gaussian function. The pulsation modes and frequencies are calculated with a non-adiabatic pulsation code. A detailed comparison of two subdwarf B models from different channels, but with the same log g and Teff, shows that their mode excitation is different. The excited frequencies are lower for the post-flash than for the post-non-degenerate subdwarf B star. This is mainly due to the differing chemical composition of the stellar envelope. A more general comparison between two grids of models shows that the excited frequencies of most post-non-degenerate subdwarfs cannot be well-matched with the frequencies of post-flash subdwarfs. In the rare event that an acceptable seismic match is found, additional information, such as mode identification and log g and Teff determinations, allows us to distinguish between the two formation channels.
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