Infrared Photometry and Evolution of Mass-Losing AGB Stars. II. Luminosity and Colors of MS and S Stars
Infrared Photometry and Evolution of Mass-Losing AGB Stars. II. Luminosity and Colors of MS and S Stars
复制标题
红外光度测量和质量损失 AGB 恒星的演化。
DOI：
--
复制
发表时间：
2008
期刊：
影响因子：
--
通讯作者：
M. Busso
中科院分区：
文献类型：
--
作者：
R. Guandalini;M. Busso
语境。渐近巨星分支（AGB）阶段标志着低质量和中等质量恒星演化的结束。我们对它们喷射包膜的机制的理解以及对它们对质量返回星际介质和星系化学演化的贡献的评估，都由于对富碳源和富氧源的光度和质量损失率了解不足而受到阻碍。目标。我们计划建立标准，允许根据红外通量对各种类型的 AGB 恒星的光度（以及随后的质量损失率）进行更定量的测定。在本文中，我们特别关注富含 O 和 s 元素的 MS、S 星，并包括一小部分 SC 星。方法。我们根据内在（单）和外在（双）长周期变量样本重新分析 MS、S、SC 恒星的绝对辐射热星等和颜色。我们将辐射热校正作为近红外和中红外颜色的函数，采用一组恒星作为参考，可以在大波长范围内详细重建光谱能量分布。我们确定了绝对 HR 图，并将 S 型巨星的光度和颜色与先前推导的富含 C 的 AGB 恒星的光度和颜色进行了比较。光度估计也根据对富 O 米拉有效的现有周期光度关系进行验证。结果。 S星的辐射热光度与富含C的AGB星的辐射光度几乎没有区别。相反，它们的星周包膜更薄且不透明。尽管有最后一个特性，红外波长仍然占主导地位，最蓝的恒星在 H 或 K（短）波段具有最大发射量。无论如何，近中红外色差都小于 C 星。基于富含 O 的 Miras 的周期-光度关系和相同变量的幅度-颜色关系，我们展示了如何推断迄今为止未知的视差源的近似距离（因此内部参数）。我们认为大多数源的质量相当小（<2 M�）；那么，挖掘可能不足以有效地让 C/O 比率超过 1。
Context. Asymptotic giant branch (AGB) phases mark the end of the evolution for low- and intermediate-mass stars. Our understanding of the mechanisms through which they eject the envelope and our assessment of their contribution to the mass return to the interstellar medium and to the chemical evolution of Galaxies are hampered by poor knowledge of their luminosities and mass loss rates, both for C-rich and for O-rich sources. Aims. We plan to establish criteria permitting a more quantitative determination of luminosities (and subsequently of mass loss rates) for the various types of AGB stars on the basis of infrared fluxes. In this paper, in particular, we concentrate on O-rich and s-elementrich MS, S stars and include a small sample of SC stars. Methods. We reanalyze the absolute bolometric magnitudes and colors of MS, S, SC stars on the basis of a sample of intrinsic (single) and extrinsic (binary) long period variables. We derive bolometric corrections as a function of near- and mid-infrared colors, adopting as references a group of stars for which the spectral energy distribution could be reconstructed in detail over a large wavelength range. We determine the absolute HR diagrams, and compare luminosities and colors of S-type giants with those, previously derived, of C-rich AGB stars. Luminosity estimates are also verified on the basis of existing period-luminosity relations valid for O-rich Miras. Results. S star bolometric luminosities are almost indistinguishable from those of C-rich AGB stars. On the contrary, their circumstellar envelopes are thinner and less opaque. Despite this last property the IR wavelengths remain dominant, with the bluest stars having their maximum emission in the H or K(short) bands. Near-to-mid infrared color differences are in any case smaller than for C stars. Based on period-luminosity relations for O-rich Miras and on Magnitude-color relations for the same variables we show how approximate distances (hence intrinsic parameters) for sources of so far unknown parallax can be inferred. We argue that most of the sources have a rather small mass (<2 M� ); dredge-up might then be not effective enough to let the C/O ratio exceed unity.