Study Of The Infrared Properties Of S Stars According To Photometric Data And ISO SWS Spectra

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 â… , 6 stars for Group â…¡ and 2 stars for Group â…¢) 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...