【作者】 杨孝鸿；

【导师】 王建成； 陈培生；

【作者基本信息】 中国科学院研究生院（云南天文台） ， 天体物理， 2006， 博士

【摘要】 S星是一种特殊的红巨星，通常被作为正常的M星与C星之间的中间状态，与“第三次挖掘”过程和S-过程紧密联系，而发生在恒星表面上的C／O和S-核素的变化正见证了M-MS-S-SC-C的演化。然而随着对无Tc（锝）S星的认识，人们逐渐意识到S星不再完全是真正的AGB星，而是一个受到双星S星（无TcS星，外赋S星）污染的一个星类。通常将处于AGB演化阶段的有TcS星称为内禀S星，将处于双星中的无TcS星称为外赋S星。GCGSS星表（S星星表）里就可能含有大量的无Tc星。S星在红外波段上的性质引起了人们广泛的兴趣，不仅因为S星与M星、C星在大气、星周环境里化学物质构成上的异同可能会表现在红外波段上，还因为内禀S星和外赋S星有着不同的红外特性。为此，本论文基于IRAS、2MASS及MSX的测光数据和ISO SWS01光谱对S星作了进一步的研究，主要结论如下： 1)对GCGSS星表中收录的1347个S星进行了交叉证认，从而获得528个S星的2MASS和IRAS的红外测光数据，其中有174个S星的MSX的A波段数据。基于这些2MASS、IRAS和MSX的测光数据，我们研究了内禀S星和外赋S星的红外特性，从而获得了有效区分两类S星的方法。利用这种方法我们筛选出256个内禀S星的候选星和147个外赋S星的候选星，并认为GCGSS星表中可能有38±8％的外赋S星。 2)我们处理和分析了ISO观测到的所有17颗S星（2颗为外赋S星，另15颗为内禀S星）的ISO SWS01光谱数据，并且初步证认了分子吸收特征的候选载体。依据S星在IRAS LRS中的分类和尘埃物质损失率（?）的增加，15颗内禀S星可以被分为三组。研究表明外赋S星和三个不同的组有各自不同的红外特性。2个外赋S星和组Ⅰ中的7个内禀S星有非常相似的ISO SWS01光谱，它们的光谱正反映了来自恒星光球的辐射，因为由于较低的物质损失率在其中心星周围形成不了厚的拱星尘埃壳层。对外赋S星，几乎没有发现任何冷尘埃的信息；对于组Ⅰ，有的表现出60μm红外超，而有的没有。组Ⅱ有较厚的尘埃壳层，它与组Ⅰ相比其光谱的峰值波长已向红端移动，并且它们的ISO SWS01光谱上显示出明显的尘埃发射特征。在组Ⅲ中的内禀S星的ISO SWS01光谱呈现出较红的连续谱，其峰值波长大约为7μm，表明在其中心星周围存在着一个由较高的物质损失率所形成的很厚的拱星壳层，以至于在红外波段几乎完全遮挡了中心星。 3)分子H₂O、CO、CO₂和SiO对在S星红外光谱上出现的分子吸收特征有重要的影响。分子HCN和CS通常只出现在C星中，然而我们从S星的光谱中发现了HCN和CS分子可能对光谱的某些吸收特征也有贡献，如4.1μm吸收特征的候选载体为CS，仅出现在IRAS01159+7220（S Cas）和IRAS19126-0708（WAql）中的2.90—3.30μm吸收特征的候选载体为HCN。更多还原

【Abstract】 S stars are peculiar red giants, which are often thought to be an intermediate phase between normal M stars and C stars in the earier time and of which some properties result from the "third dradge up" and the s-process. The progression of spectral type M to MS to S to SC may be caused not only by a changing C/O ratio but also by an increase in the abundance of s-process elements. However, the study of Tc-poor S stars suggestes that two categories of S stars exist. Intrinsic S stars (Tc-rich S stars), following the evolution sequence M-S-C, are indeed lying on the AGB phase, but extrinsic S stars (Tc-poor S stars ) are in binary system, and their element abundances appear to have been altered by transfer from the progenitor of a white dwarf companion. General Catalogue of Galactic S Stars (GCGSS) may include a great deal of extrinsic S stars in binary system. The infrared properties of S stars are interesting, not only because similarities and differences between S stars and M/C stars in chemical components may be exhibited in infrared bands but also because intrinsic and extrinsic S stars have different infrared properties with each other. Therefore, this Ph. D. thesis will further study the infrared properties of S stars on the base of data from IRAS, 2MASS, MSX and ISO. Main results are obtained as follows:1) The cross-indentification between the objects in GCGSS and the 2MASS, IRAS and MSX observations is made, and thereby 528 2MASS and IRAS counterparts, including 174 MSX counterparts, are obtained to be stuied samples. After the analysis of these samples, an effective method for distinguishing extrinsic S stars from intrinsic S stars is presented and is employed to pick out the candidates of extrinsic and intrinsic S stars. Consequently, We obtain 256 candidates of intrinsic S stars and 147 candidates of extrinsic S stars, and deduce that about 38 + 8 percent of GCGSS objects is of S stars in binary system.2) ISO SWS01 spectra of 17 S stars (including 2 extrinsic S stars and 15 intrinsic S stars) are presented, and the candidate carriers of molecular absorption features are preliminarily identified. The 15 intrinsic S stars can be divided into three groups (7 stars for Group Ⅰ, 6 stars for Group Ⅱ and 2 stars for Group Ⅲ) according to their IRAS low-resolution spectra and the increase of dust mass loss ratio. The analysis for S stars shows that 2 extrinsic S stars and the three groups have different更多还原