Analysis On The Abundance Of Elements Sc And Mn In Stars Of Different Stellar Populations

Stellar abundances is a good trace to investigate the structure and chemical evolution ofthe Galaxy. With the development of astronomical technology and instruments，a largeamount of stellar spectra have been obtained, and the stellar abundances of many elementshave been present in detail which ensure us to do some statistic analysis on chemicalevolution of the Galaxy. We choose F and G stars as our sample objects to investigate theabundance trends of Sc and Mn in the disk and the halo of the Galaxy.To obtain a more reliable result in general, we do a statistical analysis on the abundanceratios of [Sc/Fe] and [Mn/Fe] in a large sample of F and G dwarfs. The observations includestwo parts: one is the publicated data from11literatures publicated between2000and2011,the other is the new abundances derived from15F and G-dwarfs we observed using the2.16m telescope and its attached coude spectrograph in Xinglong Observatory of the NationalAstronomical Observatories. Finaly, we have compiled a large catalogue of792sample starsincluding of367thin disk stars,303thick disk stars and128halo stars.Our paper is consists of5sections. In Sect.1, we present an introductin about the structureof the Milky Way and a short review of observational studies on stellar abundances of Mn andSc in recent years. Sect.2describes the kinematical method to claasify the stellar populationsand select three subsamples of the sample stars representative of the thin disk, the thick diskand the halo stars. In Sect.3. we get elemental abundances of15F and G dwarfs. In Sect.4we describe the construction of the large catalogue of elemental abundances of Sc and Mnfrom published data and analyze the completeness of the sample stars.In Sect.5. we report ourfindings on the chemical properties of Sc and Mn in the three subsamples, such as the trendsof [Sc/Fe] and [Mn/Fe] along with the metallicity [Fe/H], the mean Galactocentric distancesRmand the maximum vertical distance from the Galactic Plane Z_max.Based on the statistical analysis, we concluded some important results as follows:（1）The Sc elements is overabundance in metal-poor stars, still [Sc/Fe] shows differenttrends with metallicity [Fe/H] for different stellar populations.For the thin disk stars, the[Sc/Fe] abundance trend decreases linearly to solar values at [Fe/H]=0.While for the thickdisk stars, the trend of [Sc/Fe] shows a “knee” downward at about[Fe/H]=-0.7,which like the the trend of elements, just as expected if Sc belongs to the element family. As well asthe thin and the thick disk stars overlap in metallicity and have no serious difference with[Sc/Fe] vs.[Fe/H] in the range-0.8<[Fe/H]<-0.1, and we can not separate the thin disk starsfrom the thick one based on the the abundance of Sc element. The medial value of [Sc/Fe] ofthick disk stars is higher than that of thin disk stars seriously.（2）The Mn elements is underabundance in metal-poor stars, while [Mn/Fe] showsdifferent trends with metallicity [Fe/H] for different stellar populations.The thin and the thickdisk stars overlap in metallicity and have no serious difference with [Mn/Fe] vs.[Fe/H] in therange-1.0<[Fe/H]<-0.1, so we can not separate the thin disk stars from the thick one based onthe the abundance of Mn element. The medial value of [Mn/Fe] of the thin disk stars is higherthan that of thick disk stars.（3）The metallicity ranges of individual stellar populations: the range of the thin disk starsis-1.09<[Fe/H]<0.37; the range of the thick disk stars is-2.66<[Fe/H]<0.37;and the range ofthe halo stars is-2.61<[Fe/H]<-0.55. It means the three populations overlap greatly inmetallicity, and can not be seperated only by stellar metallicity.（4）The stellar average orbital radius distribution: the range of the thin disk stars is6.44kpc<R_m<10.50kpc; the range of the thick disk stars is4.62kpc<Rm<10.81kpc; the rangeof the halo stars is4.31kpc<Rm<11.80kpc. Therefore, there is overlap in the average Rmamong the thin disk stars, thick disk stars and halo stars.（5）The distribution of the maximum distance from the Galactic plane Zmax: the range ofthe thin disk stars is Z_max<1kpc; the range of the thick disk stars is Zmax=0.02³.67kpc; therange of the halo stars is Z_max>1kpc. It means there are some overlap between the thin andthick disk stars, as well as between the thick disk and halo stars in Z_max.（6）The kinematics of thin disk, thick disk and halo stars are significantly different,especially for the speed V_LSR. the range of the thin disk stars is VLSR>-60km/s; the range ofthe thick disk stars is-175km/s<VLSR<-60km/s; the range of the halo stars is VLSR<-175km/s.In addition, the three populations of the velocity dispersions are also different, the velocitydispersion of stars increases from the thin disk to the thick disk and then to the halo stars. Theabundances of [Sc/Fe] and [Mn/Fe] have no obvious correlation with the kinematic velocities. （7）Both [Sc/Fe] and [Mn/Fe] abundance of the thin disk, thick disk and halo stars arerelation with R_mand Z_max, that means exist Sc and Mn elements abundance gradient.