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arXiv 1306.5439astro-ph.SR
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含锝和不含锝的Miras的周期-质量损失率关系

Period -- mass-loss rate relation of Miras with and without technetium

Stefan Uttenthaler

备注：
Accepted for publication in A&A (5 pages, 2 figures, 1 on-line table); final version (language corrected)
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摘要：

目的：我们报告的发现，米拉变量和没有吸收线的元素锝（Tc）占据两个不同的区域在图中的近中红外颜色与脉动周期。Tc是最近或正在进行的混合事件的指标，称为第三次疏浚（3DUP），近中红外颜色，如（K-[22]）颜色，其中[22]是WISE空间天文台的22微米波段，是恒星尘埃质量损失率的指标。研究方法：我们从文献中收集了有关的Tc含量，脉动周期，近红外和中红外星等的190多个变星的渐近巨星分支（AGB）属于Miras。样本自然偏向于光学AGB星，它们具有低到中等（尘埃）质量损失率。结果如下：我们表明，尘埃质量损失率和脉动周期之间存在着一个明确的关系，如果作出区分之间的Tc-穷人和Tc-丰富的Miras。令人惊讶的是，在给定的时间段内，贫Tc的Miras在（K-[22]）中比富Tc的Miras更红;即它们比富Tc的Miras具有更高的质量损失率。少数恒星偏离了这一趋势;对这些例外给出了物理解释，如双星或高质量。结论：我们提出了两个假设来解释这种二分法，并得出结论，这两个序列形成的Tc-poor和Tc-rich Miras可能是由于不同的质量的两个群体。脉动周期与尘埃质量损失率有很强的相关性，表明脉动确实引发了尘埃驱动的风。在（K-[22]）与周期图中的位置可以用来区分3DUP前后的Miras，我们将其应用于银河系核球AGB星的样本。我们发现3DUP在内部凸起的AGB星中可能并不常见。

英文摘要：

Aims: We report the discovery that Mira variables with and without absorption lines of the element technetium (Tc) occupy two different regions in a diagram of near- to mid-infrared colour versus pulsation period. Tc is an indicator of a recent or ongoing mixing event called the third dredge-up (3DUP), and the near- to mid-IR colour, such as the (K-[22]) colour where [22] is the the 22 micron band of the WISE space observatory, is an indicator of the dust mass-loss rate of a star. Methods: We collected data from the literature about the Tc content, pulsation period, and near- and mid-infrared magnitudes of more than 190 variable stars on the asymptotic giant branch (AGB) to which Miras belong. The sample is naturally biased towards optical AGB stars, which have low to intermediate (dust) mass-loss rates. Results: We show that a clear relation between dust mass-loss rate and pulsation period exists if a distinction is made between Tc-poor and Tc-rich Miras. Surprisingly, at a given period, Tc-poor Miras are redder in (K-[22]) than are Tc-rich Miras; i.e. they have higher mass-loss rates than the Tc-rich Miras. A few stars deviate from this trend; physical explanations are given for these exceptions, such as binarity or high mass. Conclusions: We put forward two hypotheses to explain this dichotomy and conclude that the two sequences formed by Tc-poor and Tc-rich Miras are probably due to the different masses of the two groups. The pulsation period has a strong correlation with the dust-mass loss rate, indicating that the pulsations are indeed triggering a dust-driven wind. The location in the (K-[22]) vs. period diagram can be used to distinguish between pre- and post-3DUP Miras, which we apply to a sample of Galactic bulge AGB stars. We find that 3DUP is probably not common in AGB stars in the inner bulge.

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