Infrared photometry and evolution of mass-losing AGB stars - I. Carbon stars revisited
Infrared photometry and evolution of mass-losing AGB stars - I. Carbon stars revisited
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DOI：
10.1051/0004-6361:20053208
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发表时间：
2005-09
影响因子：
6.5
通讯作者：
R. Guandalini;M. Busso;S. Ciprini;G. Silvestro;P. Department;U. Perugia;Italy.;T. Observatory;U. Turku;Finland.;D. Physics;U. Torino;I. I. F. Astrophysics-I.;Cosmic Physics;Roma
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文献类型：
--
作者：
R. Guandalini;M. Busso;S. Ciprini;G. Silvestro;P. Department;U. Perugia;Italy.;T. Observatory;U. Turku;Finland.;D. Physics;U. Torino;I. I. F. Astrophysics-I.;Cosmic Physics;Roma
作为对星系渐近巨星(AGB)在红外(IR)波长的再分析的一部分，我们讨论了一个碳星样本(357)，其中存在质量损失率、近红外测光和距离估计。对于252个源，我们从MSX(6C)和ISO-SWS星表收集了中IR通量。大多数恒星的光谱能量分布高达21μm，有些(1/3)高达45μm。这种宽波长覆盖使我们能够获得可靠的测辐射热星等。讨论了我们的样品的性质，重点是具有天文测量距离的~70颗恒星。我们发现，中红外通量对于估计具有尘埃包层的恒星的星等至关重要。我们构建了HR图，并表明发光率与基于Schwarzschild判据的模型预测相当吻合，这与文献中广泛争论的相反。C星的亮度问题似乎并不存在。从米拉变星和半正则C变星的相对数量来看，我们认为这些类别之间的切换不太可能与热脉冲有关。这两个种群的相关性随着进化的不同而不同，米拉斯在最后阶段占据主导地位。我们还分析了质量损失率，质量损失率随着光度的增加而增加，但扩散可能是由于依赖于许多参数(例如，不同的恒星质量和为恒星风提供动力的不同机制)。相反，红外颜色可以很好地监测质量损失率，特别是如果扩展到20μm或更高，其中AGB信封的行为就像黑体一样。从这些颜色讨论了各类C星的演化状态。
As part of a reanalysis of galactic Asymptotic Giant Branch (AGB) stars at infrared (IR) wavelengths, we discuss a sample (357) of carbon stars for which mass loss rates, near-IR photometry and distance estimates exist. For 252 sources we collected mid-IR fluxes from the MSX (6C) and the ISO-SWS catalogues. Most stars have spectral energy distributions up to 21 μ m, and some (1/3) up to 45 μ m. This wide wavelength coverage allows us to obtain reliable bolometric magnitudes. The properties of our sample are discussed with emphasis on ~70 stars with astrometric distances. We show that mid-IR fluxes are crucial to estimate the magnitude of stars with dusty envelopes. We construct HR diagrams and show that the luminosities agree fairly well with model predictions based on the Schwarzschild's criterion, contrary to what is widely argued in the literature. A problem with the brightness of C stars does not appear to exist. From the relative number of Mira and Semiregular C-variables, we argue that the switch between these classes is unlikely to be connected to thermal pulses. The relevance of the two populations varies with the evolution, with Miras dominating the final stages. We also analyze mass loss rates, which increase for increasing luminosity, but with a spread that probably results from a dependence on a number of parameters (like e.g. different stellar masses and different mechanisms powering stellar winds). Instead, mass loss rates are well monitored by IR colours, especially if extended to 20 μ m and beyond, where AGB envelopes behave like black bodies. From these colours the evolutionary status of various classes of C stars is discussed.